Physiological and biological mechanisms of bisphosphonate action

Thesis

Bisphosphonates (BPs) are stable analogues of pyrophosphate widely used for the treatment of bone diseases characterised by increased bone resorption. Studies over the years have shown that the pharmacological potencies of BPs are dependent both on their binding affinities for bone mineral and on their inhibitory actions on osteoclasts. In addition, potential effects on other cell types present locally in the environment of skeletal tissues have been reported.

The present study systematically evaluated the relative mineral-binding affinities of individual BPs of clinically relevance in mixtures of these compounds and the changes with elution pH by using column chromatography with ceramic hydroxyapatite and fluoroapatite combined with mass spectrometric identification and quantitation of the individual BPs. The results indicate that pH has a profound effect on the ionisation of the phosphonate and R2 functional groups, with BPs having greater affinities at lower pH as shown by increased retention times. Moreover, two other approaches, namely using Langmuir adsorption isotherms and competition assays based on fluorescent BP, have been developed to assess the mineral-binding capacities and dissociation constants of BPs. These results suggest that there are substantial differences among BPs in their binding to hydroxyapatite.

From the cellular aspect of my study, I present evidence for the anti-apoptotic effects of BPs in osteocytes and osteoblasts. However, the study of prosurvival signalling pathways involved in these cells needs to be optimised.

The work described in this thesis provides novel insights into the physiological and biological mechanisms of BP action. My project has provided a better knowledge of the physicochemical properties of BPs, which are highly relevant to their differential distributions within bone, their biological potencies, and their durations of action. Additionally, the cell culture studies may provide new information on the cellular effects of BPs on osteocytes and osteoblasts.

Authors: Duan, X

• Publication date: 2011
• DOI: 10.5287/ora-d5djkbkzd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: Oxford University, UK
• Language: English
• Keywords: osteocytes; mineral binding; bisphosphonates; bone
• Subjects: Orthopaedics