oa Editorial from Guest Editor [Hot Topic: Calcium Metabolic Disorders and Treatment –Boning Up for the Future (Guest Editor: Peter Vestergaard)]

Calcium metabolic disorders are frequent. The most frequent calcium-metabolic condition is osteoporosis with loss of mineral from the skeleton and an increased risk of fractures. Other frequent disorders are vitamin D deficiency leading to osteopmalacia and a number of other conditions both within the skeleton and in other organs. Until around 20 years ago the treatment options for osteoporosis were limited. With the advent of first the bisphosphonates, then the selective estrogen receptor modulators and strontium ranelate, and later parathyroid hormone and analogues, effective measures to prevent fractures became available. These drugs not only contributed to preventing bone loss but also to regain bone. This hot topic series in two papers demonstrate that new knowledge has uncovered a number of new signalling pathways in the bone that can be used to treat osteoporosis. These concepts offer the possibility of not only preventing bone loss but also to rebuild bone and thus with the existing therapies changing osteoporosis from a chronic incurable condition to a condition that not only can be treated but also cured through restoration of bone architecture and bone mass. The paper by Dr. Mosekilde et al. explores new anabolic therapies including treatments directed at the Wnt signalling system (sclerostin), parathyroid hormone (PTH) mimetics, and drugs that stimulate the calcium sensing receptor (CaSR) thus mimicking PTH action. These may all offer potent new treatment options for osteoporosis and a detailed outline of the development and potential is presented in the paper. The paper by Dr. Rejnmark et al. explores new antiresorptive pathways that may be used in addition to the pathways modulated by the bisphosphonates, and the selective estrogen receptor modulators. The paper explores osteoclast function in detail and presents new targets for therapy such as the RANK ligand antibodies that are already on the market, but also emerging pathways such as cathepsin-K inhibitors. Data on new selective estrogen receptor modulators such as bazedoxifene and lasofoxifene are also presented along with integrin antagonists, c-Src kinase inhibitors, inhibitors of the acidification process in the osteoclast lacunae, and GLP-2 agonists. .......