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Abstract
Reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) have been implicated as mediators of osteoclastic bone resorption. Xanthine oxidase (XO) a ubiquitous enzyme is widely known for its production of these ROS. We therefore evaluated the potential of XO as a source of ROS in cytokine- and hormone-induced bone resorption. XO activity in rat calvarial osteoblasts was found to be significantly elevated upon stimulation by the cytokines, TNF f and IL-1 g . These cytokines also caused a dose related increase in bone resorption of mouse calvariae, which was significantly inhibited by catalase (10 IU/ml). Allopurinol, the competitive inhibitor of XO, also caused a dose related (1-50 w M) inhibition of TNF f (20 ng/ml) and (0.01-10 w M) IL-1 g (50 IU/ml)-induced bone resorption, respectively. PTH- and 1,25-(OH)2 Vitamin D3-induced bone resorption could also be inhibited by catalase (100 IU/ml) but was unaffected by allopurinol, indicating that another mediator, other than XO, is required for hormone-induced bone resorption. These results demonstrate, that modulation of the redox balance in the bone microenvironment, which contains XO, can affect the bone resorbing process. Therefore, XO may play a pivotal role in cytokine-induced bone resorption and, if manipulated appropriately, could show a therapeutic benefit in inflammatory bone disorders such as RA.