Novel treatments for osteoporosis.

Osteoporosis is a major health problem that affects 4 to 6 million women and 1 to 2 million men in the US, with an even larger number of individuals having osteopenia or decreased bone mineral density (BMD) (1). The most significant consequence of osteoporosis is osteoporotic fractures, which in 1995 resulted in health care expenditures in the US of $13.8 billion (2). Consequently, the prevention and treatment of osteoporosis are of paramount importance. Currently, all therapeutic agents approved by the Food and Drug Administration for the treatment of osteoporosis are inhibitors of bone resorption. Although these agents are effective in stabilizing or increasing BMD and reducing the risk of fractures, their exact mechanism of action frequently is not known, and they do not increase bone formation. Alternative drug therapies that either block the function of the bone-resorbing osteoclasts or enhance the anabolic function of osteoblasts could prove beneficial to a number of patients with osteoporosis. A recent issue and, now, the current issue of the JCI feature studies on two promising new agents that operate by these complementary strategies and preserve bone mass to a significant extent in rat models of osteoporosis (3, 4). Figure 1 shows the effect of these agents on the balance between ongoing processes of bone formation and bone resorption, which together determine bone mass.