Effects of bisphosphonates on human osteoblasts as an important constituent of the bone marrow microenvironment.

Abstract

e13620 Background: Bisphosphonates (BPs) are widely used for the treatment in bone metastatic disease and for the management of osteoporosis. Their antiresorptive effects can be explained by inhibition of osteoclastic resorption, promoting osteoclast apoptosis. However, recent evidence also points to a direct action of bisphosphonates on bone-forming osteoblasts. Despite its clinical importance, the mechanisms of BPs on osteoblast function still remain poorly characterized. Methods: In this study, the influence of BPs zoledronate (zol), ibandronate (iban), and pamidronate (pam) on molecular and cellular functions of human osteoblasts was assessed by focusing on osteogenic marker gene expression, cell proliferation and viability. Results: The regulation of osteogenic markers was analyzed by quantitative real-time RT-PCR after exposure of primary osteoblasts (pOB) to different concentrations (0.01-100 μM) of zol and iban for 48 h and 72 h. The gene-expression analyses revealed an important increase in osteopontin and in osteocalcin expression with 100 μM, decrease in type I collagen alpha-2 with 0.01-100 μM zol and iban and an unchanged expression of bone sialoprotein, runt-related transcription factor 2 and osteonectin after 48 h and 72 h. Further, exposure of pOB to different zol but not to iban concentrations for 72 h resulted in a significant overexpression of alkaline phosphatase relative to control cells, except for the treatment with 100 μM. Proliferation assays demonstrated that treatment with iban and pam for 72 h did not affect the osteoblast number at concentrations of 0.01-10 μM, whereas 100 μM resulted in a notably cell growth reduction. Zol showed an inhibitory proliferation action already by 1 μM. Moreover, a significant decrease of osteoblast viability was noted after treatment with ≥ 1 μM zol after 48 h, which could be enhanced after 72 h. Conclusions: Our results demonstrated that bisphosphonates revealed prominent differences in the mode of action on human osteoblast functions. Zol, recognized as the most potent BP, reduced both the expression of osteogenic markers and the proliferation as well as the viability of human osteoblasts at concentrations in the low micro-molar range. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Novartis