Effect of recombinant human parathyroid hormone and zoledronic acid on osteoblast gene expression using multifaceted approach: An in vitro study

Abstract: BACKGROUND Bone is an endocrine organ that despite being inert in appearance constantly undergoes remodeling, in which wear and tear of bone cells occur. With more than two decades of clinical experience, the molecular mechanisms of anti-fracture drugs are not completely understood because they inhibit osteoclastic activity and differentiate the osteoblast cells. Recent studies suggest fundamentally different mechanisms of action for key anti-fracture drugs, bisphosphonates, and recombinant human parathyroid hormone (rhPTH) at the tissue level; however, their molecular basis of action has not been explored completely. Here, we showed the effect of varying concentrations of zoledronic acid (ZOL) and rhPTH on human osteogenic sarcoma cells (U2OS cells). MATERIALS AND METHODS Cellular viability, mineralization, and osteogenic gene expressions were assessed to elucidate the effects of these two prototypic drugs with diametrically different mechanisms of action. RESULTS Cellular viability was not affected either by ZOL or rhPTH alone or in tandem treatments. Osteoblastic activity increased significantly with rhPTH followed by ZOL. Further, alkaline phosphatase activity increased significantly with tandem treatment of rhPTH followed by ZOL both at the mRNA and protein levels. Moreover, osteoblastic genes (COL1A1 and osteocalcin) were significantly modulated by sequential treatment with rhPTH followed by ZOL. CONCLUSIONS We conclude that rhPTH (5 μg) treatment followed by ZOL (1 μM) showed the best anabolic or bone-forming effect. Our results warrant further research in assessing similar combinations of anti-fracture drugs, which augment osteogenesis to maximize their anabolic effects in preventing osteoporosis in susceptible individuals.