Localization of fibronectin in gingival connective tissue of the beagle dog. Immunofluorescent light microscopic findings

Quantitative evaluation of the vasculature and fibronectin localization in gingival connective tissue of smokers and non-smokers

BACKGROUND

It has been shown that tobacco is a significant risk factor for periodontal disease. The reason for decreased gingival bleeding in smokers is not known. The aim of the present study was to demonstrate the localization of fibronectin in the extracellular matrix of the inflamed gingiva of smokers and non-smokers and to evaluate the chronic effect of smoking on the gingival microvessel number (NVES) and vascular surface density (VSD).

METHODS

Seventy-four (74) adult patients with periodontitis were included in this investigation. Of these patients, 38 were smokers and 36 were non-smokers. Probing depths (PD), papillary bleeding index (PBI) of both groups, and the smoking habits of the smokers were recorded. Biopsy specimens obtained during periodontal surgery were prepared to evaluate fibronectin distribution and to quantitate the vasculature.

RESULTS

The mean VSD values of smokers and non-smokers were 6.721 +/- 1.845 and 5.721 +/- 3.118 (mean +/- SD), and the mean NVES of smokers and non-smokers was 31.582 +/- 11.810 and 30.145 +/- 15.442, respectively. The difference between the mean PD and PBI values of the 2 groups was not statistically significant. The location of the biopsy specimen, whether in the anterior or posterior area of the mouth, did not lead to any statistically significant differences between the groups. In addition, the number of years smoked and the tobacco brand used did not result in statistically significant differences. The most intense staining of fibronectin was observed beneath the epithelium around the blood vessels of the uppermost region of the connective tissue, showing a fibrillar and diffuse distribution; however, there was no significant difference between smokers and non-smokers.

CONCLUSION

The results of the present study indicate that smoking does not affect the vascular surface density, number of vessels per mm2 stroma, or fibronectin distribution in subepithelial gingival connective tissue.

Phagocytosis of fibronectin and collagens type I, III, and V by human gingival and periodontal ligament fibroblasts in vitro

BACKGROUND

Electron microscopic studies have suggested that the volume density of collagen-containing vacuoles in fibroblasts is higher in the periodontal ligament (PDL) than in the gingiva. Whether this difference reflects intrinsic differences in phagocytic capacity among the cells in these tissues is not known.

METHODS

PDL and gingival fibroblasts were isolated from subjects and cultured under identical conditions in the presence of fluorescent beads coated with collagen type I, III, or V or fibronectin. Control beads were coated with bovine serum albumin or an enamel matrix protein mixture that does not constitute part of the extracellular matrix of PDL and gingiva. After various time intervals (1 to 24 hours), the percentage of cells that had internalized beads was assessed by flow cytometry. Since alkaline phosphatase activity has been suggested to play a role in collagen phagocytosis, the activity of this enzyme was determined for all cell populations.

RESULTS

The results demonstrated the following order in the percentage of cells internalizing protein-coated beads: fibronectin > collagen type I > III > V. Internalization of collagen type I-coated beads exceeded that of beads coated with bovine serum albumin or enamel matrix proteins by 6 and 3 times, respectively. No differences were observed in collagen phagocytic activity between PDL and gingival fibroblasts, and no relationship could be demonstrated between collagen phagocytosis and alkaline phosphatase activity.

CONCLUSIONS

We conclude that differences in collagen phagocytosis between PDL and gingiva, as observed in vivo, are not likely to be explained in terms of intrinsic phagocytic capacities of these cells.

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.

Immunohistochemical expression of extracellular matrix components of normal and healing periodontal tissues in the beagle dog

Periodontal regeneration requires formation of periodontal tissues lost due to periodontal disease. To better understand the formation of new periodontal tissues during periodontal repair and regeneration, immunohistochemical expression of extracellular matrix components of normal as well as healing periodontal tissues was evaluated and compared using the avidin-biotin complex immunohistochemical technique. For this purpose, horizontal furcation defects were created around mandibular P2 and P4 of 6 dogs after extraction of P1 and P3. The root surfaces were conditioned with citric acid and expanded polytetrafluoroethylene (ePTFE) membranes were placed and retained 0.5 mm above the cemento-enamel junction. The mucoperiosteal flaps were sutured in a coronal position. Two animals were sacrificed at 2, 4, and 8 weeks, and mesio-distal tissue slices containing normal or healing periodontal tissues were demineralized, dehydrated, and embedded in paraffin. Immunohistochemical localization of type I collagen (CI), fibronectin (FN), secreted protein, acidic and rich in cysteine (SPARC), vitronectin (VN), and bone sialoprotein (BSP) was performed on 6 microns thick sections. Morphological results demonstrated that at 2 weeks after defect creation, lesions were filled primarily with granulation tissue which was gradually replaced by newly-formed fibrous connective tissue, periodontal ligament (PDL), cementum, and bone between 4 and 8 weeks. The results of immunohistochemical study revealed that at 2 weeks the granulation tissue, especially in the intercellular spaces of inflammatory cells, was intensively stained for FN and VN. At 4 and 8 weeks, staining for CI, FN, and VN was found in fibrous connective tissue, the newly-formed PDL, cementum, and osteoid. Further the attachment zone of the PDL collagen fibers to cementum showed intense staining for FN. Immunostaining for SPARC was positive in the new PDL, cementum, and bone, while staining for BSP was restricted to the new cementum and bone. Interestingly, the PDL, especially in areas adjacent to active bone formation, demonstrated intense staining for BSP. However, fibrous connective tissue and PDL proper were unstained for BSP. These results indicate that FN and VN are involved in the early stages of periodontal repair, and periodontal regeneration is achieved through formation of periodontal tissues that are composed of different matrix components specific to different types of periodontal tissues.

Distribution of fibronectin in healthy, inflamed and drug-induced gingival hyperplasia

The distribution of fibronectin (FN) in the healthy, inflamed and hyperplastic human gingiva was investigated by indirect immunofluorescence. FN appeared as a fibrillar structure in the lamina propria of the healthy gingivae. In the inflamed specimens, FN demonstrated parallel fibres, especially in the coronal areas of the tissue. In the phenytoin gingival overgrowth, tissue FN was observed as thin fibres with variable length. The thin fibres gave the appearance of penetrating the basement membrane of the epithelium. Cyclosporin A gingival enlargement could be differentiated by phenytoin lesions because of the higher length and the parallel distribution of the FN. Finally, FN was observed in the nifedipine gingival overgrowth, where a microfibrillar delicate network gave the appearance of a "cloud"-pattern of distribution. In all of the specimens, blood vessels and nerves could not be stained. These findings show that FN distribution could differentiate the structure of the gingival lesions.

Localization of fibronectin in gingival connective tissue of the beagle dog. Ultrastructural detection with ferritin and peroxidase-conjugated antibodies

Ferritin and peroxidase-conjugated antibodies were used in an indirect antibody method to localize fibronectin in gingival connective tissues. Fibronectin was found in the basal lamina beneath the epithelium and endothelium. Collagen fibrils associated with the basement membranes were also heavily coated by fibronectin. Amorphous patches of fibronectin were found adjacent to the plasma membrane of epithelial cells as well as free in the interepithelial spaces. Fibronectin was present throughout the connective tissue in close association with individual collagen fibrils, apparently serving as an interfibrillar cementing substance. Patches of fibronectin were located at the cell surface of fibroblasts, plasma cells, lymphocytes, endothelial cells, smooth muscle cells, and neutrophils. These amorphous patches were observed to connect adjacent cells across narrow spaces and to connect cells to collagen fibrils. The heavy labeling for fibronectin visualized by fluorescent microscopy around gingival blood vessels (Cho et al., 1985) can be accounted for by a heavy coating of fibronectin on the collagen fibrils and basal laminas associated with endothelial cells, as well as by the presence of abundant deposits of fibronectin along the cell membranes of endothelial cells and in the intercellular spaces of the vessel wall.