Activated protein C inhibits bisphosphonate-induced endothelial cell death via the endothelial protein C receptor and nuclear factor-κB pathways

Bisphosphonates promote apoptosis of cancer cells as well as osteoclasts in bone metastatic sites, but several clinical trials and high concentration treatment have shown that bisphosphonates have side effects that include bone loss and damage to normal cells. The aim of this study was to elucidate the protective effect and the possible mechanism of activated protein C (APC) against bisphosphonate-induced cell damage using primary cultured human umbilical vein endothelial cells (HUVECs). HUVECs were treated with APC (10 μg/ml) for 1 h, and then treated with bisphosphonates including alendronate, zoledronate and pamidronate. Bisphosphonates induced cell death in HUVECs but the cell death was blocked by treatment with APC. Bisphosphonates markedly induced caspase-3 activation, which was diminished in cells exposed to APC. Matrix metalloproteinase-2 (MMP-2) reduction and nuclear factor-κB (NF-κB) activation induced by bisphosphonates in HUVECs were also blocked by APC treatment. Furthermore, APC highly induced the expression of the endothelial protein c receptor (EPCR) in HUVEC cells. In conclusion, the present study demonstrates that APC inhibits bisphosphonate-induced endothelial cell death via EPCR-induced inactivation of caspase-3 and NF-κB, and also suggests that APC has the potential to be a therapeutic drug in various vascular diseases induced by endothelial cell damage.