In the treatment of
osteoporosis, the aim of the antiresorptive
therapy is to restore bone density by decreasing bone remodeling. The process of bone remodeling plays a role in plasma
calcium homeostasis and serves to modify bone architecture in order to meet changing mechanical needs, to maintain osteocyte viability, and to repair microdamage in bone matrix.
Estrogen deficiency results in a number of detrimental effects on bone, including suppression of osteocyte survival as well as impairment of osteoblast response to mechanical stimuli and repair of ageing bone. In this review, effects of available antiresorptive
therapies on endocrine regulations of bone metabolism in
postmenopausal osteoporosis are compared. The aim of antiresorptive treatment is to ensure adequate bone remodeling, reparation of microdamage of bone, and increased bone strength. Ideally, this effect should be maintained long-term. Several agents are approved for the treatment of
osteoporosis.
Calcitonin transiently inhibits osteoclast activity without decreasing osteoblast
collagen synthesis. Aminobisphosphonates decrease bone remodeling by decreasing osteoclast activity and by inducing osteoclast apoptosis. This allows more time for secondary mineralization to proceed to completion in the existing bone tissue mass, so increasing the mechanical resistance of bone to loading.
Estrogens and
raloxifene (a
selective estrogen receptor modulator that acts as an
estrogen agonist in bone) suppress bone remodeling to the premenopausal range, maintaining the function of osteoblasts and osteocytes. In the placebo-controlled
osteoporosis treatment trials, all the above treatments reduced the risk of fractures.
Raloxifene therapy was also associated with a favorable or neutral effect in the cardiovascular system, and a reduced incidence of
breast cancer. Selection of appropriate
drug for treatment of
postmenopausal osteoporosis should take into account the long-term effect of the
antiresorptive agent on bone. Moreover, the effects on other tissues ++should also be considered, and this encompasses both safety concerns, as well as the potentially beneficial effects on other tissues. Further investigation is needed to evaluate the different modes of action of these agents, and their long-term effects on bone and other tissues.