Adipokines and Bone Metabolism - Is there a Link?

While there is a homeostasis between bone formation and bone resorption in the healthy organism of human adults, disorders of bone metabolism can disrupt this balance resulting in pathological changes of bone density as in osteoporosis or the pathological formation of new bone structures as in ankylosing spondylitis. The activity and differentiation of bone-forming osteoblasts and bone-resorbing osteoclasts are the key factors determining the actual balance or dysbalance of bone metabolism. A wide spectrum of molecules is involved in regulating these processes including RANKL, OPG and several inflammation-related factors. Recently, the so-called adipokines, a group of cytokine-like mediators first discovered in adipose tissue but also produced by various other cell types, have been added to this spectrum. In this review, we addressed whether and how adipokines affect bone metabolism and whether there is a correlation with bone density. For this, an overview of research results from in vitro analyses, animal experiments and clinical studies is provided. The results clearly show a link between adipokines and bone metabolism. However, the actual effect of adipokines on bone in the human organism appears to be dependent on numerous other factors as there are, in part, obvious discrepancies between these results depending on the respective experimental model or clinical setting.