Oxidative stress, free radicals and bone remodeling.

Reactive oxygen species (ROS) are widely considered to be a causal factor in aging and in a number of pathological conditions, such as atherosclerosis, carcinogenesis and infarction. Their role in bone metabolism is dual, considering their effects under physiological or pathological conditions. Under physiological conditions, the production of ROS by osteoclasts helps accelerate destruction of calcified tissue, thus assisting in bone remodeling. In pathological conditions, when a bone fractures, e.g., radical generation is remarkably high. However, though the increases in osteoclastic activity and ROS production are linked in many skeletal pathologies, it remains to be clarified whether increased ROS production overwhelms antioxidant defenses, leaving the individual open to hyperoxidant stress.