[Bone mineralization and mineral status]

After initial calcification in matrix vesicles or collagen fibrils, bones are continually modified by modelling then remodelling. In bone tissue, the degree of mineralisation of bone structural units is heterogeneous, reflects the rate of bone remodelling, and can be measured using microradiography. Our model is based on the fact that bone remodelling activity and thus the duration of the secondary mineralisation of bone tissue would influence its mineral status (mainly its degree of mineralisation or bone density at tissue level). When the bone remodelling rate increases (menopause, parathyroid hormone), the degree of mineralisation of bone tissue decreases. Conversely, after a diminution of the remodelling rate induced by antiresorptive treatments, the degree of mineralisation of bone tissue increases. Strontium ranelate (PROTELOS) has been tested to date as a potential therapeutic agent in patients suffering from postmenopausal osteoporosis. Recent phase III studies (the Spinal Osteoporosis Therapeutic Intervention [SOTI] study and the TReatment Of Peripheral Osteoporosis Study [TROPOS]) show a decrease in the vertebral and extravertebral fracture risk and an increase in bone mineral density measured at lumbar spine and femoral levels. Strontium ranelate has a unique mechanism of action, since it decreases bone resorption and increases bone formation ('decoupling' agent). Our preliminary observations in animal and man reveal that, because of this dual mechanism of action, the degree of mineralisation of bone tissue and the crystal characteristics of bone mineral are maintained at normal levels. More generally, these data indicate that the mineral status of bone tissue should be systematically taken into account during histomorphometric studies of bone.