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.