In osteoporosis1 the rate of bone mass loss is accelerated and bone microstructure changes. This eventually leads to an increased fragility of bones, enhanced risk of fractures (vertebrae fracture, hip fracture, etc.) and often results in disability and premature death of elderly people. Treatment of osteoporosis patients is prolonged and expensive. High prevalence of osteoporosis among people of middle and old age requires an extensive search for effective drugs to treat and prevent of this pathology.
Bone tissue2 is known to be permanently in a process of remodelling. Bone resorption (owing to osteoclast activity) and bone formation (by osteoblasts) takes place throughout life. A person reaches peak bone mass at about 30 years of age. After that the rate of bone loss slowly increases; by the age of 75 it may be reduced by 30-50%. Osteoporosis develops when a dynamic balance between bone resorption and bone formation is impaired. This balance is regulated by a number of endogenous substances: gonadal (sex) hormones, parathyroid hormone, growth hormone, corticosteroids, calcitonin, vitamin D and its metabolites, special proteins regulating osteoclast activity (osteoprotegerin, etc.), cytokines and calcium ions. Also, mechanical strain (exercise) and hereditary factors play an important role in maintaining normal bone mass and structure.
Drugs producing favorable effect in osteoporosis belong to the following groups.
I • Hormones, their analogues and derivatives
= Gonadal (sex) hormones (estrogens, androgens)
= Calcitonins