Concentration dependent anti-inflammatory effects thrombin on polyphosphate-mediated inflammatory responses in vitro and in vivo

Recent results indicate that polyphosphate (polyP) released by human endothelial cells can function as a pro-inflammatory mediator, and it has been reported that low thrombin concentrations mediate anti-inflammatory activities. This study was undertaken to investigate whether low thrombin concentrations can modulate polyP-mediated inflammatory responses in human umbilical vein endothelial cells (HUVECs) and in mice. Concentration dependent anti-inflammatory effects of thrombin such as barrier protection, inhibition of cell adhesion molecule expression and inhibition of monocytes adhesion and migration toward human endothelial cells against polyP-mediated pro-inflammatory activities were tested in vitro and in vivo. The concentration-dependent effects of thrombin on polyP-induced nuclear factor (NF)-kappa B activation and the production of tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 were also tested. We found that at low concentrations (25-75 pM), thrombin inhibits polyP-mediated barrier disruption, the expressions of cell adhesion molecules, and leukocyte to HUVEC adhesion/migration. Interestingly, polyP-induced NF-kappa B activation and the production of TNF-alpha and IL-6 were inhibited by low thrombin concentrations in HUVECs. These anti-inflammatory functions of thrombin were confirmed in polyP-injected mice. These results suggest that thrombin at 25-75 pM may have therapeutic potential for various systemic inflammatory diseases.