The effect of endotoxins and enzymes in vitro on the release of gingival histamine

Enhancement of receptor-mediated calcium responses by phenytoin through the suppression of calcium excretion in human gingival fibroblasts

BACKGROUND AND OBJECTIVES

Gingival overgrowth caused by phenytoin is proposed to be associated with Ca²⁺ signaling; however, the mechanisms that increase the intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ) are controversial. The current study aimed to elucidate the mechanism underlying the phenytoin-induced increase in [Ca²⁺ ]_i in human gingival fibroblasts (HGFs).

METHODS

Effects of 100 μM phenytoin on [Ca²⁺ ]_i in HGFs were examined at the single-cell level using fluorescence images of fura-2 captured by an imaging system consisting of an EM-CCD camera coupled to an inverted fluorescence microscope at room temperature.

RESULTS

Exposure of HGFs to 100 μM phenytoin induced a transient increase in [Ca²⁺ ]_i in the absence of extracellular Ca²⁺ , indicating that the phenytoin-induced increase in [Ca²⁺ ]_i does not require an influx of extracellular Ca²⁺ . In addition, phenytoin increased [Ca²⁺ ]_i in HGFs depleted of intracellular Ca²⁺ stores by thapsigargin, indicating that neither Ca²⁺ release from stores nor inhibition of Ca²⁺ uptake is involved. Furthermore, the phenytoin-induced [Ca²⁺ ]_i elevation was reduced to 18.8% in the absence of extracellular Na⁺ , and [Ca²⁺ ]_i elevation upon removal of extracellular Na⁺ was reduced to 25.9% in the presence of phenytoin. These results imply that phenytoin increases [Ca²⁺ ]_i of HGFs by suppressing the Na⁺ /Ca²⁺ exchanger. Suppression of intracellular Ca²⁺ excretion is thought to enhance the Ca²⁺ responses induced by various stimuli. Analysis at the single-cell level showed that stimulation with 1 μM ATP or 3 μM histamine increased [Ca²⁺ ]_i in 20-50% of cells, and [Ca²⁺ ]_i increased in many unresponsive cells in the presence of phenytoin.

CONCLUSION

Our findings demonstrate that phenytoin induced increase in [Ca²⁺ ]_i by the inhibition of Ca²⁺ efflux in HGFs. It was also found that phenytoin strongly enhanced small Ca²⁺ responses induced by stimulation with a low concentration of ATP or histamine by inhibiting Ca²⁺ efflux. These findings suggest a possibility that phenytoin causes drug-induced gingival overgrowth by interacting with inflammatory bioactive substances in the gingiva.

A quantitative analysis of the migration, attachment, and orientation of human gingival fibroblasts to human dental root surfaces in vitro

The purpose of this study was to assess the migration, attachment, and orientation of human gingival fibroblasts to human dental roots over a period of 21 days in vitro. The fibroblasts were incubated with a total of 120 periodontally diseased and non-diseased root slices (200 microns thickness) which had been treated in the following manner: 1) Root planed diseased root (DT); 2) Root planed and citric acid demineralized diseased root (DTD); 3) Non-treated diseased root (DNT); 4) Citric acid demineralized diseased root (DNTD); 5) Non-diseased control (ND); 6) Citric acid demineralized non-diseased root (CA); 7) Citric acid and collagenase digested non-diseased root (CAC); 8) EDTA demineralized non-diseased root (E); and 9) EDTA-demineralized and collagenase-digested non-diseased root (EC). The results showed that that most active phase of cell attachment and orientation occurred during the first 10 days of the experiment. Statistical differences were observed between the variables, and, in terms of cell attachment and orientation to the root slices, it was concluded that: 1) Root planing improves diseased roots; 2) Acid demineralization subsequent to root planing improved diseased roots to such an extent as to render them comparable to non-diseased roots; 3) Citric acid demineralization alone improved diseased roots to the same extent as root planed diseased roots; 4) The exposure of collagen fibrils resulting from acid demineralization of the tools is not the sole reason for the improvement of the root surface, but rather a combination of the exposed collagen fibrils with the creation of a more hospitable environment was found to be responsible.

Initial attachment of fibroblast-like cells to periodontally-diseased root surfaces in vitro

The precise factors mediating both initial cell attachment and longer term connective tissue reattachment after tissue destruction due to periodontal disease are not known. An in vitro model was used to assess initial attachment of fibroblast-like cells to periodontally-diseased root surfaces. Root fragments were obtained from freshly extracted teeth from 6 different patients. Individual roots were prepared such that a comparison could be made of initial attachment to non-instrumented diseased root surface, curetted diseased root surface and the non-diseased, non-instrumented portion of the same root. The amount of hard tissue removed by instrumentation was quantitated and kept constant between 0.9-1.0 mm. The unsterilized fragments were incubated with human gingival fibroblasts (HGF) for 1 h at 37 degrees, after which the roots were first washed to remove non-adherent cells and then photographed. The number of attached cells per unit area was quantitated from the photographs using a grid system. No significant differences could be detected between the numbers of cells attached to the 3 types of root surfaces studied on the individual roots or between any of the roots studied. Thus, initial attachment of HGF to diseased root surfaces is not inhibited by the presence of plaque or endotoxins.

Effect of various root surface treatments on the viability and attachment of human gingival fibroblasts

Periodontally involved extracted human teeth were either untreated or were treated with root planing, citric acid, or root planing followed by citric acid. Following incubation of the roots, in the presence of normal human gingival fibroblasts for varying periods of time, cells were assayed for viability by radioactive label (51Cr). In addition, the ability to promote attachment and growth of gingival fibroblasts, by root treatment as above, was observed. The results of multiple experiments in each category indicated strongly that none of the roots, regardless of treatment or nontreatment, had any significant adverse affect on the viability of the cells. However, only root-planed roots, whether or not citric acid was used, promoted cell attachment and growth.