Inhibition of fibroblast proliferation and collagen synthesis by capsular material from Actinobacillus actinomycetemcomitans.

Cytotoxic effects of bacteria found in dental plaque are usually attributed to lipopolysaccharides (LPS) or ill-defined toxins. Many bacteria implicated in periodontal disease produce surface exopolymers (capsules) recently shown to stimulate bone resorption. Capsular material and LPS extracted from Actinobacillus (Haemophilus) actinomycetemcomitans were purified and examined for their effects on cultures of human gingival fibroblasts. DNA and collagen synthesis were significantly inhibited by capsular material (0.1-50 micrograms/ml). LPS caused only modest inhibition of DNA synthesis at 10 and 50 micrograms/ml, and had no effect on collagen synthesis. Release of lactate dehydrogenase from fibroblasts was not increased by LPS nor by capsular material, showing that the inhibitory effects were not due to cell death. Capsular material, but not LPS, caused a pronounced increase in cell size; a doubling of the nuclear area occurred within 72 h exposure. These results indicate that the capsule of A. actinomycetemcomitans may play an active role in the tissue destruction characterising inflammatory periodontal disease.