Abstract
Background: Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a widely recognised dental side effect of bisphosphonate therapy in which the key finding is a non-healing exposed necrotic bone in the oral cavity. The mechanisms underlying BRONJ are poorly understood. Previous studies have indicated that the mevalonate pathway (MVP) and an anti-angiogenic effect of bisphosphonates may play a role in the pathogenesis of BRONJ.
Aims: To determine the effects of zoledronic acid (ZA) on angiogenic gene expression in primary human osteoclast (OST) cells, and to investigate replacement of the MVP with geranylgeraniol (GGOH) in the ZA treated OST cells.
Methods: Three OST cell lines were generated from peripheral blood mononuclear cells using ACCUSPIN™ System-HISTOPAQUE (Sigma). The osteoclast phenotype was confirmed by phase contrast microscopy and tartrate-resistant acid phosphatase staining. Gene expression profiling was carried out using the RT2 ProfilerTM PCR Array System (SABiosciencesTM). Genes coding for 84 human angiogenic factors were determined. The data were analysed using the SABiosciences Excel template for gene analysis and GraphPad PRISM.
Results: The results showed that among the 84 angiogenic genes tested, the treatment of OST with ZA caused significant (p ≤ 0.05, Fold regulation ≥ ± 2) up-regulation of only one gene - the chemokine ligand 10 gene (CXCL10). The co-addition of GGOH with ZA resulted in up-regulation of the integrin alpha V gene (ITGAV) and down-regulation of eight angiogenic genes including CXCL10, platelet cell adhesion molecule (PECAM1), serpin peptidase inhibitor member 1 (SERPINF1), chemokine ligand 1 (CXCL1), chemokine ligand 9 (CXCL9), insulin-like growth factor 1 (IGF1), transforming growth factor beta receptor 1 (TGFβR1) and endoglin (ENG).
Conclusions: Osteoclasts in vitro responded to ZA alone and with GGOH by up and down regulating a number of genes, and several families of functional gene groups identified. These genes may play a role in the pathogenesis of BRONJ.