Ultrastructural study of cultured human gingival fibroblasts exposed to endotoxin

Host-bacteria crosstalk at the dentogingival junction

The dentogingival junction is of crucial importance in periodontal host defense both structurally and functionally. Oral bacteria exert a constant challenge to the host cells and tissues at the dentogingival junction. The host response is set up to eliminate the pathogens by the innate and adaptive defense mechanisms. In health, the commensal bacteria and the host defense mechanisms are in a dynamic steady state. During periodontal disease progression, the dental bacterial plaque, junctional epithelium (JE), inflammatory cells, connective tissue, and bone all go through a series of changes. The tissue homeostasis is turned into tissue destruction and progression of periodontitis. The classical study of Slots showed that in the bacterial plaque, the most remarkable change is the shift from gram-positive aerobic and facultatively anaerobic flora to a predominantly gram-negative and anaerobic flora. This has been later confirmed by several other studies. Furthermore, not only the shift of the bacterial flora to a more pathogenic one, but also bacterial growth as a biofilm on the tooth surface, allows the bacteria to communicate with each other and exert their virulence aimed at favoring their growth. This paper focuses on host-bacteria crosstalk at the dentogingival junction and the models studying it in vitro.

Effect of pH on endotoxin affinity for metal-ceramic alloys

STATEMENT OF PROBLEM

Crevicular pH may modify bacterial endotoxin affinity for high-noble metal-ceramic alloys.

PURPOSE

Porphyromonas gingivalis lipopolysaccharide (LPS) affinity for 3 metal-ceramic alloys at 3 different pH levels was compared in vitro by measuring adsorption to and release from the alloy surface.

MATERIAL AND METHODS

Metallographically polished disks were fabricated from Pd-Ag-Sn, Au-Pd-Ag-Sn-In, and Au-Pd-In-Ga alloys. Clean disks were placed individually into 1 mL at pH 6.5, 7.0, or 7.5 phosphate-buffered saline solution containing 0.9 endotoxin units per square millimeter tritiated LPS (n = 3 disks per alloy-pH group). The disks were incubated for 24 hours at 37 degrees C before being transferred to LPS-free buffer and incubated, again for 24 hours at 37 degrees C, to evaluate elution. This transfer continued at 24-hour intervals up to 96 hours total elution incubation. Lipopolysaccharide adsorption to and elution from disks was determined through liquid scintillation spectrometry. Adsorption data were evaluated with a 2-way analysis of variance (alpha=.05) and the post hoc Tukey honestly significant difference test.

RESULTS

Lipopolysaccharide adsorption values ranged from 0.48 +/- 0.04 EU/mm(2) for the Au-Pd-Ag-Sn-In alloy at pH 7.5 to 0.75 +/- 0.04 EU/mm(2) for the Pd-Ag-Sn alloy at pH 6.5. Alloy type (P=.0001) and environmental pH (P=.0001) significantly influenced adsorption. Adsorption to the Pd-Ag-Sn and Au-Pd-In-Ga alloys at pH 6.5, 7.0, and 7.5 were similar and decreased with increasing pH. In contrast, adsorption to the Au-Pd-Ag-Sn-In alloy was significantly less than to other alloys at pH 6.5 but did not differ at other pH levels. Lipopolysaccharide release from the alloy surface could not be detected.

CONCLUSION

P. gingivalis LPS affinity for metal-ceramic alloys was modified by environmental pH. The degree of LPS adsorption depended on the composition and surface chemistry of each alloy.

Lipopolysaccharide increases cell surface-associated fibronectin in fibroblasts in vitro

This study assessed the fibronectin expression by fibroblasts derived from noninflamed and inflamed gingiva by measuring the amount of cell surface-associated fibronectin and fibronectin released into the medium. The effects of added lipopolysaccharide from Porphyromonas gingivalis, Prevotella nigrescens and Escherichia coli on both types of fibroblasts were also studied. In the absence of lipopolysaccharide, the amounts of the two types of fibronectin were significantly larger in the fibroblasts from inflamed than from noninflamed gingiva. The specific lipopolysaccharide had no effect on the amount of fibronectin released into the medium by either fibroblast type. The amount of cell surface-associated fibronectin increased significantly when lipopolysaccharide (0.1 and 1 microgram/ml) was added to the cells from the noninflamed gingiva (the effect was evident in the order: P. gingivalis>P.nigrescens>E. coli). Lipopolysaccharide from P. gingivalis significantly increased the cell surface-associated fibronectin even at a low concentration of lipopolysaccharide (0.01 microgram/ml). In fibroblasts from the inflamed gingiva, only the lipopolysaccharide from P. gingivalis was effective in increasing the amount of cell surface-associated fibronectin. Our findings showed that the fibronectin expression was increased in the fibroblasts from inflamed gingiva and that lipopolysaccharide from P. gingivalis increased the cell surface-associated fibronectin.

Effect of Campylobacter rectus LPS on plasminogen activator-plasmin system in human gingival fibroblast cells

The plasminogen activator (PA)-plasmin system is implicated in the degradation of the extracellular matrix in inflammation through activation of metalloproteases and prekallikrein. We examined the activation of the PA-plasmin system in human gingival fibroblast cells (Gin-1 cells) following treatment with lipopolysaccharide (LPS) from Campylobacter rectus, which is frequently detected at sites of periodontal disease. The C. rectus LPS stimulated the plasmin activity in the conditioned medium of Gin-1 cells in a time- and dose-dependent manner, and C. rectus LPS also stimulated the PA activity in the conditioned medium. The PA produced by Gin-1 cells was determined to be urokinase PA (uPA), as preincubation of Gin-1 conditioned medium with anti-uPA antiserum completely inhibited the PA activity while that with anti-tPA antiserum had no inhibitory effect. The concentration of PA inhibitor-1 (PAI-1) in the conditioned medium was decreased by the addition of C. rectus LPS. Therefore, the enhancement of plasmin activity in the conditioned medium was dependent on increased uPA activity via the decrease of the PAI-1 level of Gin-1 cells treated with C. rectus LPS. Furthermore, the conditioned medium of Gin-1 cells treated with C. rectus LPS showed significantly increased kallikrein activity, indicating the conversion of prekallikrein to kallikrein, which converts kininogen into kinin. These findings suggest that C. rectus LPS is a potent stimulator of inflammation of gingival tissue which acts through stimulation of the PA-plasmin system.

Alterations of fibroblast metabolism in early ligature-induced periodontitis in the cynomolgus monkey

Cellular and biochemical observations were made of fibroblasts harvested from ligature-induced periodontitis and treated gingivitis areas in four adult female cynomolgus monkeys (Macaca fascicularis) to define the changes that occur in the early periodontitis lesion. Compared with fibroblasts from the treated sites, fibroblasts from the diseased areas had a significantly higher rate of proliferation, produced about two-thirds the amount of total protein and collagen, and failed to respond to TGF-beta, which normally stimulates extracellular matrix formation in mesenchymal cells. The diseased cells were also deficient in the activity of poly(ADP-ribose) synthetase, an enzyme involved in the repair of DNA breaks such as occur from the insults of superoxide and other active radicals present in inflamed areas. Although the precise nature of these biochemical defects is not fully elucidated, they may have an important bearing on chronic periodontitis cases with a "downhill" course.

Platelet-derived growth factor reduces the inhibitory effects of lipopolysaccharide on gingival fibroblast proliferation

Lipopolysaccharide from a variety of bacterial sources is known to inhibit gingival fibroblast proliferation and synthetic activity and has been implicated in the pathogenesis of periodontal inflammation. However, it may be involved not only in pathogenesis but also be responsible for delayed wound healing following periodontal therapy. The aim of this investigation was to determine whether the inhibitory effect of LPS on gingival fibroblast proliferation could be reversed by growth factors. Human gingival fibroblasts were cultured in the presence of varying concentrations of platelet-derived growth factor (PDGF) or Salmonella enteritidis LPS to determine the optimal concentrations for stimulation and inhibition of proliferation respectively. The effect of PDGF on LPS inhibition of fibroblast proliferation was studied by combining PDGF and LPS together at the outset of the experimental period or adding PDGF to cells which had been previously primed with LPS. Cell proliferation was monitored by incorporation of 3H-thymidine into precipitable DNA. The results indicated that maximal inhibition of fibroblast proliferation was obtained with 50 micrograms/ml LPS and maximal stimulation of proliferation with 5 ng/ml PDGF. PDGF was found to restore the proliferative activity of the cells exposed to LPS to approximately 60% of their control counterparts. A similar value was obtained for cultures exposed to PDGF after an extended priming period of LPS exposure. Subtle differences were noted in the time taken for cells to complete their cell cycle in the various culture conditions and this may reflect variations in subpopulations of cells in their response to various mitogenic stimuli. Overall the results indicate that PDGF has the capacity to significantly negate and reverse the inhibitory effects of LPS on human gingival fibroblast proliferation.

Mechanism of endotoxin inhibition of human gingival fibroblast attachment to type I collagen

Bacterial endotoxin inhibits the attachment of human gingival fibroblasts to collagen. The present study attempted to elucidate the possible mechanism of this inhibition. Two mechanisms were considered: direct toxicity to the cells and steric interference. Collagen substrates were prepared by rat type I collagen being air-dried in the wells of 24 multi-well plates. Experimental collagen substrates were treated with 50 micrograms of endotoxin/well, while untreated collagen substrates served as controls. Two mL of cell suspension (10(4) cells/mL) was added to each well, and these were incubated at 37 degrees C for two h. The average cell number/mm2 attached to experimental and control substrates was determined. Cell attachment to endotoxin-treated collagen was inhibited by 78%, compared with that to untreated collagen. The washing of the endotoxin-treated collagen for two h did not affect the inhibition of cell attachment, whereas after 24 h of washing, cell attachment was inhibited by 54%, compared with that to untreated collagen. Pre-incubation of the cells in endotoxin for two h did not affect their attachment to collagen. The addition of fetal calf serum (15%) to the experimental system completely reversed the inhibition of fibroblast attachment to endotoxin-treated collagen. These findings suggest that endotoxin interferes with fibroblast attachment to collagen through a steric phenomenon, possibly by blocking the binding sites on the collagen molecule recognized by the membrane receptor for collagen.

Bacterial endotoxin inhibits migration, attachment, and orientation of human gingival fibroblasts in vitro and delays collagen gel contraction

The purpose of this study was to assess the effect of endotoxin adsorbed to dental surfaces and to collagen type I on the migration, attachment, and orientation of human gingival fibroblasts (HGF). Transversely cut porcine tooth root slices (RS), 200 micron thick, were prepared. Half of the RS obtained were partially demineralized in EDTA. Half of the demineralized and non-demineralized RS were incubated with 400 micrograms/mL of endotoxin for 24 hr, whereas the other half were maintained in PBS and served as controls. Experimental and control RS were placed on confluent layers of HFG and cultured for six days. Cell migration toward and cell attachment to the periphery of the RS and the formation of oriented cell sheets were assessed by means of photographic techniques. Additionally, six-day-old cultures were fixed and processed for SEM observation. In separate experiments, the effect of endotoxin on cell attachment to collagen type I and on contraction of three-dimensional collagen gels was assessed. It was found that: (i) bacterial endotoxin inhibited migration and attachment of HGF to both demineralized and non-demineralized cementum and interfered with the development of oriented cellular structure: (ii) the inhibitory effect was significantly more pronounced for non-demineralized than for demineralized cementum: (iii) the morphology of HGF attached to endotoxin-treated dental surfaces was altered compared with that of their controls: and (iv) bacterial endotoxin inhibited cell attachment to collagen type I and delayed the contraction of collagen gel.

Growth inhibitory effects of endotoxins from Bacteroides gingivalis and intermedius on human gingival fibroblasts in vitro

Purified endotoxin or lipopolysaccharide from Bacteroides gingivalis and Bacteroides intermedius caused a similar dose-dependent inhibition of growth of cultured human gingival fibroblasts as determined by 3H-thymidine incorporation and direct cell count. Approximately 200 micrograms/ml endotoxin caused a 50% reduction in 3H-thymidine uptake of logarithmically growing cells. Inhibition of growth was similar in cultures of fibroblasts derived from either healthy or diseased human gingiva. When examining the change in cell number with time of exposure in culture, the rate of proliferation was significantly suppressed during the logarithmic phase of growth. However, the cells recovered so that the rate of proliferation, although reduced, was sufficient to produce a cell density similar to the control cells with prolonged culture. The endotoxins were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The profiles of the Bacteroides endotoxins were different. B. gingivalis endotoxin showed a wide range of distinct bands indicating a heterogeneous distribution of molecular species. Endotoxin from B. intermedius exhibited a few discrete low molecular weight bands, but the majority of the lipopolysaccharides electrophoresed as a diffuse band of high molecular weight material. The apparent heterogeneity of the two Bacteroides endotoxins and the similarity in growth inhibitory capacity suggest that growth inhibitory effects of these substances cannot be attributed to any polysaccharide species of endotoxin.

Kinin generation in the gingival inflammatory response to topically applied bacterial lipopolysaccharides

A water-soluble lipopolysaccharide from Salmonella enteritidis and a phenol-soluble lipopolysaccharide from Leptotrichia buccalis were applied topically to the healthy marginal gingivae of beagle dogs. Saline was applied to contralateral areas as an internal control. Increases in vascular permeability were monitored by measurement of gingival fluid, and the collected gingival fluid samples were assayed for kininogenase and kinin activities. Both lipopolysaccharides induced an inflammatory response, as indicated by increased gingival fluid flow. Kininogenase-kinin activities paralleled the increases in gingival fluid flow, with the highest values being associated with peak increases in gingival fluid. The results indicate that both lipopolysaccharides, although different in lipid solubility, penetrate healthy sulcular epithelium and initiate an inflammatory response which is mediated in part by the kallikrein-kinin system. Interrelationships between this system and other inflammatory mediators suggest that kinin generation not only plays a role in the early phases of acute gingival inflammation, but may also contribute to the activation of other mediators appearing later in the response and in chronic inflammatory lesions.

Inhibitory effect of periodontally diseased root extracts on the growth of human gingival fibroblasts

Cementum shavings obtained from periodontally diseased and nondiseased areas of 100 removed, single-rooted teeth were extracted with either pyrogen-free water (PFW) for 5 minutes, 1 M citric acid for 5 minutes or 45% phenol-PFW for 90 minutes at 65 degrees C. The extracts were membrane-filtered, dialyzed exhaustively versus PFW, lyophilized, weighed and then dissolved in complete growth medium. The phenol-water or citric acid extracts of cementum shavings from periodontally diseased roots were positive for endotoxin by the limulus lysate assay (LLA). Pyrogen-free water extracts of diseased or phenol-water extracts of nondiseased cementum shavings were negative, or only slightly positive, respectively, for endotoxin by LLA. Media containing the various extracts were added to logarithmically growing cultures of human gingival fibroblasts (HGF). Separate cultures of HGF were exposed to Escherichia coli endotoxin at concentrations of 50, 100, 250 and 500 micrograms/ml to determine the growth-inhibitory effects of a known endotoxin. Cell growth was analyzed by measuring the incorporation of tritiated thymidine into cells. Suppression of HGF growth from 30 to 49% by E. coli endotoxin was concentration-dependent and linear over the concentration range of endotoxin tested. Pyrogen-free water extracts of diseased (endotoxin negative) or phenol-water extracts of nondiseased cementum shavings (slightly endotoxin positive) did not effect HGF growth. However, citric acid or phenol-water extracts of diseased cementum shavings (highly endotoxin positive) significantly suppressed HGF growth 58% and 61%, respectively. These results indicate that citric acid is effective in removing cytotoxic substances, presumably endotoxin, from cementum shavings and suggest that citric acid treatment is effective clinically in detoxifying periodontally diseased root surfaces.