Bisphosphonate-associated osteonecrosis of the jaws (BP-ONJ) is a side effect primarily in patients receiving highly potent nitrogen-containing bisphosphonates. The exact etiopathology is unknown. In addition to reduced bone remodeling, there may also be an impact on soft tissues. The impact of nitrogen- (ibandronate, pamidronate, zoledronate) and non-nitrogen-containing bisphosphonates (clodronate) on human umbilicord vein endothelial cells (HUVEC), fibroblasts and osteogenic cells was analyzed employing cell viability testing and a scratch wound assay. The impact on the cell morphology of vital-stained osteogenic cells was investigated by cell visualization (confocal laser scanning microscopy). Pamidronate and zoledronate had the greatest negative impact on all cell lines, whereas the impact of ibandronate and clodronate was less distinct. The effect of clodronate on HUVEC and fibroblasts was particularly marginal. BP-ONJ could be a multifactorial event with multicellular impairments. This might result in altered wound healing. The increased impact of the highly potent bisphosphonates, particularly on non-bone cells, may explain the higher occurrence of BP-ONJ.
Bisphosphonate-associated osteonecrosis of the jaws (BP-ONJ) is one of the main side effects in patients treated with bisphosphonates for metastasis to the bone or osteoporosis. BP-ONJ usually occurs in patients treated with highly potent nitrogen-containing bisphosphonates. The exact mechanism of action and etiopathology is still unknown. In addition to inhibition of bone remodelling, an anti-angiogenetic effect has become the focus of research. The aim of these study was to investigate the effect of different bisphosphonates on human umbilicord vein endothelial cells (HUVEC) and endothelial progenitor cells (EPC), which play an important role in angiogenesis. Using varying concentrations, the impact of one non-nitrogen-containing bisphosphonate (clodronate) and three nitrogen-containing bisphosphonates (ibandronate, pamidronate and zoledronate) on HUVEC and EPC was analysed. The biologic behaviour of HUVEC after incubation with different bisphosphonates was measured in a Boyden migration assay as well as in a 3D angiogenesis assay. The number of apoptotic cells was measured by Tunnel assay. To underline the importance of neoangiogenesis in the context of BP-ONJ, we measured the EPC number after incubation with different bisphosphonates in vitro. HUVEC and EPC were significantly influenced by bisphosphonates at different concentrations compared with the non-treated control groups. The nitrogen-containing bisphosphonates pamidronate and zoledronate had the greatest impact on the cells, whereas clodronate followed by ibandronate was less distinct on cell function. These results underline the hypothesis that inhibited angiogenesis induced by bisphosphonates might be of relevance in the development and maintenance of BP-ONJ. The increased impact by highly potent bisphosphonates on HUVEC and EPC may explain the high prevalence of BP-ONJ in patients undergoing this treatment.
These results support the theory that BP-ONJ is a multifactorially caused disease because several cell lines of the oral cavity which are responsible for integrity and wound healing are negatively affected by nitrogen-containing bisphosphonates. Perioperative interruption of bisphosphonate application during dental surgical procedures--if possible--might be feasible to promote better wound healing.
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