Microbial mechanisms in the pathogenesis of destructive periodontal diseases: a critical assessment

Cytotoxicity of Porphyromonas gingivalis toward cultured human gingival fibroblasts

Direct cytotoxicity of black-pigmented anaerobic rods was studied on the confluent monolayer of human gingival fibroblasts in vitro. Only strains of Porphyromonas gingivalis caused morphological alteration (cell-rounding) and notable depression of viability of fibroblasts. To determine the location of the cytotoxicity, bacterial surface components, i.e., outer membrane, lipopolysaccharide, fimbriae and outer membrane vesicles were prepared from P. gingivalis and their cytotoxicity was assessed. Among these preparations, only outer membrane vesicles are supposed to have high affinity to human gingival fibroblasts, and the cytotoxicity of outer membrane vesicles was found to be much stronger than that of the other constituents. This cytotoxic factor seemed to consist largely of protein and to be associated with the enzyme activity of outer membrane vesicles. The effects of some protease inhibitors and L-cysteine on the cytotoxicity of outer membrane vesicles suggest that the mechanism of cell-rounding is different from that of cell death.

Interactions of Porphyromonas gingivalis with epithelial cells

The invasion of gingival epithelial cells by certain pathogenic periodontal bacteria may account for their presence within diseased gingival tissue. To dissect the initial steps of a potential invasion pathway for the periodontal pathogen Porphyromonas gingivalis, laboratory and clinical bacterial isolates were tested for their interactions with a human oral epithelial cell line (KB). Several P. gingivalis strains immobilized on filters could bind oral epithelial cells. Quantitative adherence assays supported these results. The invasion of epithelial cells by P. gingivalis 33277 was measured by assay and confirmed by transmission electron microscopy. These preliminary results demonstrate that certain P. gingivalis strains are capable of internalization by human oral epithelial cells in vitro.

The effects of Acacia arabica gum on the in vitro growth and protease activities of periodontopathic bacteria

The antibacterial activity of acacia gum was assessed using fresh isolates and reference strains of Actinobacillus actinomycetemcomitans, Capnocytophaga spp., Porphyromonas gingivalis, Prevotella intermedia and Treponema denticola. A fine aqueous suspension of gum was produced by sonication and then a soluble fraction isolated by centrifugation and membrane filtration. These preparations were incorporated into columbia agar at doubling concentrations. Growth of P. gingivalis and P. intermedia cultures on the agar was inhibited by whole gum sonicate at concentrations of 0.5-1.0% w/v. Both species showed reduced susceptibility when horse blood was present in the agar. The gum soluble fraction did not inhibit growth of any bacterial culture. The effect of acacia on bacterial proteases was examined with cell sonicates from log phase broth cultures. Enzyme activities were determined by fluorimetric assay with various synthetic peptide substrates. Most protease activities reduced in the presence of 0.5% w/v gum sonicate, with the trypsin-like activities of P. gingivalis and P. intermedia proving most sensitive. The gum soluble fraction was nearly always less inhibitory than the sonicate. The action of acacia gum against suspected periodontal pathogens and their enzymes suggests that it may be of clinical value.

Inhibition of bone DNA and collagen production by surface-associated material from bacteria implicated in the pathology of periodontal disease

Gentle extraction of oral bacteria implicated in the pathogenesis of periodontal disease, Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, or Eikenella corrodens, with saline removes the extracellular components while leaving the bacteria intact. This readily-solubilized surface-associated material (SAM) has been demonstrated to significantly inhibit DNA and collagen synthesis by murine calvaria at concentrations as low as 10 ng/ml. DNA and collagen synthesis in isolated calvarial osteoblasts were also inhibited by these SAM preparations with similar dose responses. The inhibitory effect of these bacterial expolymers was blocked by 1 microM indomethacin. The potent inhibitory actions on bone synthesis of the SAM from these bacteria may contribute to the alveolar bone loss found in patients with periodontal disease.

Fatty acids of healthy and periodontally diseased root substance in human teeth

In this comparative study, samples of root substance from healthy and periodontally diseased human teeth were analyzed for fatty acids by means of a gas-chromatographic technique. The sample preparation procedure allowed specimens from individual teeth to be analyzed. The content of the fatty acids C16:0, C16:1, C18:0, and C18:1 in the superficial layer of the periodontally diseased teeth was significantly higher than that of healthy teeth. In the inner layer, there was no such difference. Four different 3-hydroxy fatty acids (3-OH C14:0, 3-OH C15:0, 3-OH C16:0, and 3-OH C17:0) were identified by combined gas-chromatography/mass-spectrometry in the tooth substance of periodontally diseased teeth. This indicates the presence of lipid A, which is the toxic component of bacterial lipopolysaccharides.