title: Effects of continuous calcitonin treatment on osteoclasts derived from cocultures of mouse marrow stromal and spleen cells.
abstract: BACKGROUND
  Continuous calcitonin (CT) treatment for bone diseases associated with increased bone resorption may be followed by prolonged depression of osteoclast response to CT. The mechanisms of this "escape" phenomenon remain unclear.
  
  
  METHODS
  We examined the effects of continuous CT treatment on cell formation, calcitonin receptor (CTR) expression, response to CT, and bone resorption of osteoclasts in a coculture of mouse marrow stromal and spleen cells in the presence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Cells were cocultured and treated with salmon CT (sCT) for 7, 14, or 21 days. The effects of continuous CT treatment on osteoclast formation was determined by quantitation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNCs). CTR expression in osteoclasts was determined by binding of [125I]sCT in autoradiography. Bone resorption and CT responsiveness were assessed by examining the formation of resorption pits and by enumerating osteoclast reattachment on dentine slices after sCT rechallenge.
  
  
  RESULTS
  TRAP-positive MNCs appeared in cocultures treated with sCT and were similar in number and morphology to those in control cultures, regardless of the concentration and duration of sCT treatment. A decrease in CTR expression was identified as a loss of silver grains from the TRAP-positive cells in cocultures receiving sCT treatment for 14 or 21 days. Partial recovery of CTR expression in TRAP-positive cells was evident in cocultures treated with sCT for only the first 7 days of coculture. TRAP-positive MNCs in cocultures treated with sCT for 14 or 21 days were resistant to the rechallenge with sCT. They attached to dentine slices and caused numerous resorption pits compared with control cells and cells treated with sCT for the first 7 days of coculture (p < 0.01).
  
  
  CONCLUSIONS
  These findings suggest that the escape phenomenon that develops after continuous CT treatment may be due, at least in part to: 1) loss of responsiveness to CT in existing osteoclasts; and 2) development of new osteoclasts that are CTR-deficient and, therefore, refractory to CT rechallenge.
authors.affiliation: School of Dentistry, College of Medicine, National Taiwan University, Taipei.
authors.forename: B Y
authors.initials: BY
authors.lastname: Liu
authors.forename: J T
authors.initials: JT
authors.lastname: Wang
authors.forename: J S
authors.initials: JS
authors.lastname: Leu
authors.forename: C P
authors.initials: CP
authors.lastname: Chiang
authors.forename: C C
authors.initials: CC
authors.lastname: Hsieh
authors.forename: H W
authors.initials: HW
authors.lastname: Kwan
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects; D001862:Bone Resorption / Q000188:drug therapy; D002116:Calcitonin / Q000378:metabolism / Q000494:pharmacology*; D018920:Coculture Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010010:Osteoclasts / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D018003:Receptors, Calcitonin / Q000032:analysis / Q000235:genetics; D013154:Spleen / Q000166:cytology; D017154:Stromal Cells / Q000166:cytology / Q000187:drug effects
chemical_list: D012333:RNA, Messenger; D018003:Receptors, Calcitonin; D002116:Calcitonin