Osteoporosis is a high-prevalence disease, particularly in developed countries, and results in high costs both to
the individual and to society through associated fragility fractures. There is an urgent need for identification of novel drug
targets and development of new anti-osteoporotic agents. Between 30 and 80% of osteoporotic fractures cannot be prevented
despite current treatments achieving relative fracture risk reduction of up to 20%, 50%, and 70% for non-vertebral,
hip and spine fractures, respectively. Traditionally, the decline in gonadal hormones has been studied as the sole hormonal
determinant for the loss of bone mineral density in osteoporosis. However, recent studies have identified receptors for
numerous non-gonadal hormones such as PTH, angiotensin II, leptin, adiponectin, insulin and insulin-like growth factor-1
on the osteoblast lineage cells that directly regulate bone turnover. These hormones are also involved in the pathogenesis
of metabolic syndrome risk factors, particularly hypertension, type-II diabetes and obesity. By activating their respective
receptors on osteoblastic lineage cells, these hormones appear to act through a common mechanism by down-regulating
receptors for activation of nuclear factor kappa B ligand (RANKL) and up-regulating osteoprotegerin (OPG) with inverse
responses for adiponectin. Receptors for amylin, gastric inhibitory polypeptide and ghrelin and have also been identified
on the osteoblast lineage cells although the roles of these receptors in bone turnover are controversial or poorly studied.
Moreover, bone turnover may be independently regulated by modulation of osteoclast-osteoblast function and bone marrow
adiposity. Leptin appears to be the only hormone that is a known regulator of both bone mineralisation and bone adiposity.