[Cytokines and osteoporosis]

During the last few years, progress has been made towards the understanding of local regulation of bone remodelling especially in relation to osteoporosis. Cytokines have shown to be powerful regulators of bone resorption and formation, though under superior control from oestrogen/testosterone, parathyroidhormone and 1,25(OH)2D3. Some of the cytokines primarily enhance osteoclastic bone resorption e.g. IL-1 (Interleukin-1), TNF (Tumor Necrosis Factor) and IL-6 (Interleukin-6), while others primarily stimulate bone formation e.g. TGF-beta (Transforming Growth Factor), IGF (Insulin-like Growth Factor) and PDGF (Platelet Derived Growth Factor). Another category has complex functions with stimulation of bone formation in vitro but stimulation of bone resorption in vivo; IFN-gamma (Interferon-gamma) belongs to this category. The bone remodelling cycle is delicately regulated, and even a slight disturbance in this regulation can cause a pathological state in the bone such as osteoporosis. This paper will try to give a survey of some of the processes that regulate bone metabolism and hopefully contribute to understanding the changes in the remodelling related to osteoporosis.