The effect of Bisphosphonates on Human Mesenchymal Stem Cell Behaviour and its implication on Titanium Osseointegration

Introduction: Bisphosphonates (BPs) are chemical analogues related to pyrophosphate; they are well known inhibitors of osteoclast activity. During the last 40 years, BPs have been used in the clinic to treat various bone diseases characterized by excessive bone resorption, such as osteoporosis, malignant bone diseases, and hypercalcaemia of malignancy. Human mesenchymal stem cells (hMSCs) possess regenerative properties with the ability to differentiate into different cell types and are the first osteogenic cells to colonise an implant’s surface. Titanium implants have been successfully used to replace missing teeth for over 30 years. The effectiveness of the implant depends on successful osseointegration; coating dental implants with different types of bone-inducing material has shown positive effects on osseointegration. The effects of BPs on the proliferation and osteogenic differentiation of hMSCs are still unclear. Aims: The aim of this project is to investigate the effect of two types of commonly used BPs (alendronate (ALE) and pamidronate (PAM)) on hMSC proliferation and osteogenic differentiation, the extended effect of a single low-dose of BPs on hMSCs proliferative and osteogenic behaviour as well as the epigenetics changes, and the role of a low dose of BPs as an adjunct treatment to implant therapy. Methods and material: The experiments were conducted in a two-dimensional in vitro model, which consisted of hMSCs suspended in growth medium in a sterile culture vessel. We investigated the effect of these drugs on cell proliferation, migration, DNA methylation. Osteogenic genes and differentiation markers were measured including calcium, collagen type I and alkaline phosphates activity (ALP). Results: The data suggest that treating cells with a lower concentration (100 nM and 10 nM) of the drug induces significant stimulation of hMSCs osteogenic differentiation. Treating cells with a single low dose of drugs (100 nM and 10 nM) may permanently change the osteogenic behaviour of the hMSCs even after passaging the cells. A low dose of BPs significantly upregulated osteogenic markers, including calcium, collagen type I, and alkaline phosphatase. There was also a significant effect on proliferation and cell migration on the titanium surface. Finally, the data showed that there was a significant effect on epigenetic phenotype via DNA methylation. Conclusion: These experiments indicate that a lower concentration of drugs may play an integral role in enhancing the proliferation and osteogenic differentiation of hMSCs. Furthermore, these findings suggest that BPs may more than compensate for the established positive effects of osteoclasts in bone density in osteoporotic patients. The enhancement of osteogenesis could also point to the use of low-dose BPs as an adjunct to implant placement in patients. Therefore, the administration of BPs may be pivotal in accelerating osseointegration and the bone healing process following implant placement