Cell cycle-specific growth inhibitory effect on human gingival fibroblasts of a toxin isolated from the culture medium of Actinobacillus actinomycetemcomitans.

A toxin isolated from the growth medium of Actinobacillus actinomycetemcomitans by ammonium sulfate precipitation was shown to inhibit irreversibly the multiplication of human gingival fibroblasts. DNA histograms from flow cytometric measurements showed that the cells accumulated preferentially in the G2 phase of the cell cycle. Such cells exhibited sheetlike protrusions, and an increased frequency of micronuclei was evident in cells treated with low concentrations of the toxin. Toxin-treated cells were viable for several weeks, as shown by staining with trypan blue and fluorescein diacetate, and the general cell metabolism as measured by oxygen consumption was unimpaired.