title: RANKL inhibition with osteoprotegerin increases bone strength by improving cortical and trabecular bone architecture in ovariectomized rats.
abstract: BACKGROUND
  Ovariectomy (OVX) results in bone loss caused by increased bone resorption. RANKL is an essential mediator of bone resorption. We examined whether the RANKL inhibitor osteoprotegerin (OPG) would preserve bone volume, density, and strength in OVX rats.
  
  
  METHODS
  Rats were OVX or sham-operated at 3 mo of age. Sham controls were treated for 6 wk with vehicle (Veh, PBS). OVX rats were treated with Veh or human OPG-Fc (10 mg/kg, 2/wk). Serum RANKL and TRACP5b was measured by ELISA. BMD of lumbar vertebrae (L(1)-L(5)) and distal femur was measured by DXA. Right distal femurs were processed for bone histomorphometry. Left femurs and the fifth lumbar vertebra (L(5)) were analyzed by muCT and biomechanical testing, and L(6) was analyzed for ash weight.
  
  
  RESULTS
  OVX was associated with significantly greater serum RANKL and osteoclast surface and with reduced areal and volumetric BMD. OPG markedly reduced osteoclast surface and serum TRACP5b while completely preventing OVX-associated bone loss in the lumbar vertebrae, distal femur, and femur neck. Vertebrae from OPG-treated rats had increased dry and ash weight, with no significant differences in tissue mineralization versus OVX controls. muCT showed that trabecular compartments in OVX-OPG rats had significantly greater bone volume fraction, vBMD, bone area, trabecular thickness, and number, whereas their cortical compartments had significantly greater bone area (p < 0.05 versus OVX-Veh). OPG improved cortical area in L(5) and the femur neck to levels that were significantly greater than OVX or sham controls (p < 0.05). Biomechanical testing of L(5) and femur necks showed significantly greater maximum load values in the OVX-OPG group (p < 0.05 versus OVX-Veh). Bone strength at both sites was linearly correlated with total bone area (r(2) = 0.54-0.74, p < 0.0001), which was also significantly increased by OPG (p < 0.05 versus OVX).
  
  
  CONCLUSIONS
  OPG treatment prevented bone loss, preserved trabecular architecture, and increased cortical area and bone strength in OVX rats.
authors.affiliation: Metabolic Disorders Research, Amgen, Thousand Oaks, California, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Ominsky
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Li
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Asuncion
authors.forename: Mauricio
authors.initials: M
authors.lastname: Barrero
authors.forename: Kelly S
authors.initials: KS
authors.lastname: Warmington
authors.forename: Denise
authors.initials: D
authors.lastname: Dwyer
authors.forename: Marina
authors.initials: M
authors.lastname: Stolina
authors.forename: Zhaopo
authors.initials: Z
authors.lastname: Geng
authors.forename: Mario
authors.initials: M
authors.lastname: Grisanti
authors.forename: Hong-Lin
authors.initials: HL
authors.lastname: Tan
authors.forename: Timothy
authors.initials: T
authors.lastname: Corbin
authors.forename: James
authors.initials: J
authors.lastname: McCabe
authors.forename: William S
authors.initials: WS
authors.lastname: Simonet
authors.forename: Hua Z
authors.initials: HZ
authors.lastname: Ke
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Kostenuik
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000033:anatomy & histology*; D005260:Female; D053244:Osteoprotegerin / Q000502:physiology*; D010052:Ovariectomy; D053245:RANK Ligand / Q000037:antagonists & inhibitors* / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D053244:Osteoprotegerin; D053245:RANK Ligand