Glucocorticoid decreases circulating osteoprotegerin (OPG): possible mechanism for glucocorticoid induced osteoporosis

Background. Osteoporosis is a well known side-effect of long-term treatment with glucocorticoids. However, the precise mechanism of this disorder is unclear. Recently, osteoprotegerin (OPG) [osteoclastogenesis inhibitory factor (OCIF)] has been identified as a novel cytokine, which inhibits differentiation and activation of osteoclast. In the present study, in order to clarify the roles of OPG in the development of glucocorticoid-induced osteoporosis, we measured circulating OPG before and after glucocorticoid therapy. Methods. The study subjects were 12 patients (five males, seven females, 53.4+/-4.8 [SE] years) with various renal diseases that required glucocorticoid therapy. All patients received glucocorticoids for the first time. Treatment was initiated at an average dose of 32.5+/-3.0 mg per day. Serum OPG was measured using enzyme-linked immunosorbent assay (ELISA). Laboratory data, markers of bone metabolism and circulating OPG were compared before and after treatment for 4 weeks. Results. Serum OPG prior to glucocorticoid therapy was positively and independently correlated with serum creatinine. Serum OPG decreased significantly (P < 0.0001) from 1.03 +/- 0.14 to 0.77 +/- 0.12 ng/ml after short-term administration of glucocorticoids. Furthermore, serum osteocalcin as a marker of bone formation was also reduced markedly (P=0.001). On the other hand, there were no remarkable changes in serum calcium, total alkaline phosphatases, creatinine and intact parathyroid hormone in response to glucocorticoid administration. Conclusion. These findings indicate that short-term administration of glucocorticoids significantly suppresses serum OPG and osteocalcin. It might participate in the development of glucocorticoid-induced osteoporosis via an enhancement of bone resorption and suppression of bone formation.