Effect of corticosteroids on human osteoclast formation and activity T Hirayama, A Sabokbar and N A Athanasou Department of Pathology, Nuffield Department of Orthopaedic Surgery, University of Oxford, Nuffield Orthopaedic Centre, Oxford OX3 7LD, UK (Requests for offprints should be addressed to N A Athanasou; Email: nick.athanasou@ndos.ox.ac.uk) Abstract Chronic corticosteroid treatment is known to induce bone loss and osteoporosis. Osteoclasts are specialised bone- resorbing cells that are formed from mononuclear phago- cyte precursors that circulate in the monocyte fraction. In this study we have examined the effect of the synthetic glucocorticoid, dexamethasone, on human osteoclast for- mation and bone-resorbing activity. Human monocytes were cultured for up to 21 days on glass coverslips and dentine slices, with soluble receptor activator for nuclear factor B ligand (RANKL; 30 ng/ml) and human macrophage-colony stimulating factor (M-CSF; 25 ng/ml) in the presence and absence of dexamethasone (10 8 M). The addition of dexamethasone over a period of 7 and 14 days of culture of monocytes (during which cell prolifer- ation and differentiation predominantly occurred) resulted in a marked increase in the formation of tartrate-resistant acid phosphatase-positive multinucleated cells and an increase in lacunar resorption. The addition of dexametha- sone to monocyte cultures after 14 days (when resorptive activity of osteoclasts had commenced) reduced the extent of lacunar resorption compared with cultures to which no dexamethasone had been added. The addition of dexamethasone to osteoclasts isolated from giant cell tumours of bone significantly inhibited resorption pit formation. Our findings indicate that dexamethasone has a direct effect on osteoclast formation and activity, stimulat- ing the proliferation and differentiation of human osteo- clast precursors and inhibiting the bone-resorbing activity of mature osteoclasts. Journal of Endocrinology (2002) 175, 155–163 Introduction Corticosteroid-induced bone loss is the most common form of secondary osteoporosis. It is usually the result of excessive treatment with corticosteroids and results in loss of cortical and cancellous bone and an increased risk of pathological fracture (Adachi 1997, Eastell et al. 1998, Van Staa et al. 2000). Osteoporosis secondary to corticosteroid treatment is believed to result from effects on the bone remodelling unit, with osteoblastic bone formation and osteoclastic resorption being affected (Nishimura & Ikuyama 2000). Bone loss after corticosteroid treatment is characterised by an initial phase of rapid bone resorption followed by a more chronic phase in which bone is lost gradually (Bressot et al. 1979, Dempster 1989); it has been noted that there is an increase in osteoclast numbers and sites of lacunar resorption in the bones of patients receiving steroid treatment. This increase in osteoclast numbers is thought to be due to either increased formation of osteoclasts or increased osteoclast survival (Manolagas 2000). Osteoclasts are formed by fusion of bone marrow- derived precursors that circulate in the monocyte fraction of peripheral blood (Fujikawa et al. 1996). Osteoclast formation requires the presence of macrophage-colony stimulating factor (M-CSF) and involves interaction between CD14 + monocytes, which express the receptor activator of nuclear factor (NF)-B (RANK), and RANK ligand (RANKL), which is expressed by osteoblasts (Tanaka et al. 1993, Matsuzaki et al. 1998, Quinn et al. 1998, Yasuda et al. 1998). Although the precise manner in which corticosteroids stimulate osteoclast formation is unclear, these compounds are known to enhance osteo- clast formation from marrow precursors in vitro and to increase and decrease respectively osteoblast expression of RANKL and osteoprotegerin, the soluble decoy receptor for RANK (Hofbauer et al. 1999). The effect of cortico- steroids on osteoclast bone-resorbing activity is controver- sial, with both enhancement and inhibition of the activity of bone-resorbing cells being reported (Raisz et al. 1972, Teitelbaum et al. 1981, Reid et al. 1986, Tobias & Chambers 1989). Corticosteroids are also believed to influence osteoclastic bone resorption by enhancing osteo- clast apoptosis (Tobias & Chambers 1989, Dempster et al. 1997). In this study, we have sought to analyse the effect of corticosteroids on human osteoclast formation and activity. We have defined the proliferation and activation stages of human osteoclast formation and, in this way, determined the effect of the synthetic glucocorticoid, dexamethasone, on the formation and resorbing activity of human osteo- clasts formed from circulating precursors. In addition, we 155 Journal of Endocrinology (2002) 175, 155–163 0022–0795/02/0175–155  2002 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology.org