Thrombin activates the growth, cell-cycle kinetics, and clustering of human dental pulp cells

Thrombin is activated during vascular injury and inflammation of the dental pulp. In the present study, we found that thrombin can stimulate the proli feration of pulp cells in a dose-dependent manner as analyzed by modified M TT assay. The cell number increased by 1.6, 1.77, and 2.14-foId over that o f control after exposure to 5, 10, and 20 units/ml of thrombin for 5 days. Flow cytometry studies also found that thrombin (10 units/ml) can induce th e cell cycle progression of pulp cells after 24 h of incubation, as reveale d by increasing the proportion of cells in the S phase and the G2/M phase f rom 29 to 72%. Moreover, exposure to thrombin (>5 units/ml) for 3 days led to marked clustering of pulp cells. We concluded that thrombin can regulate the growth, cell cycle progression, and functional reorganization of the p ulp tissue during pulp healing and inflammatory processes.