title: Single-Limb Irradiation Induces Local and Systemic Bone Loss in a Murine Model.
abstract: Increased fracture risk is commonly reported in cancer patients receiving radiotherapy, particularly at sites within the field of treatment. The direct and systemic effects of ionizing radiation on bone at a therapeutic dose are not well-characterized in clinically relevant animal models. Using 20-week-old male C57Bl/6 mice, effects of irradiation (right hindlimb; 2 Gy) on bone volume and microarchitecture were evaluated prospectively by microcomputed tomography and histomorphometry and compared to contralateral-shielded bone (left hindlimb) and non-irradiated control bone. One week postirradiation, trabecular bone volume declined in irradiated tibias (-22%; p < 0.0001) and femurs (-14%; p = 0.0586) and microarchitectural parameters were compromised. Trabecular bone volume declined in contralateral tibias (-17%; p = 0.003), and no loss was detected at the femur. Osteoclast number, apoptotic osteocyte number, and marrow adiposity were increased in irradiated bone relative to contralateral and non-irradiated bone, whereas osteoblast number was unchanged. Despite no change in osteoblast number 1 week postirradiation, dynamic bone formation indices revealed a reduction in mineralized bone surface and a concomitant increase in unmineralized osteoid surface area in irradiated bone relative to contralateral and non-irradiated control bone. Further, dose-dependent and time-dependent calvarial culture and in vitro assays confirmed that calvarial osteoblasts and osteoblast-like MC3T3 cells were relatively radioresistant, whereas calvarial osteocyte and osteocyte-like MLO-Y4 cell apoptosis was induced as early as 48 hours postirradiation (4 Gy). In osteoclastogenesis assays, radiation exposure (8 Gy) stimulated murine macrophage RAW264.7 cell differentiation, and coculture of irradiated RAW264.7 cells with MLO-Y4 or murine bone marrow cells enhanced this effect. These studies highlight the multifaceted nature of radiation-induced bone loss by demonstrating direct and systemic effects on bone and its many cell types using clinically relevant doses; they have important implications for bone health in patients treated with radiation therapy.
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Wright
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Jeroen T
authors.initials: JT
authors.lastname: Buijs
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Hun-Soo
authors.initials: HS
authors.lastname: Kim
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Coats
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Scheidler
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Sutha K
authors.initials: SK
authors.lastname: John
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: She
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Sreemala
authors.initials: S
authors.lastname: Murthy
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Ma
authors.affiliation: Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Helen J
authors.initials: HJ
authors.lastname: Chin-Sinex
authors.affiliation: Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Teresita M
authors.initials: TM
authors.lastname: Bellido
authors.affiliation: Department of Biomedical Engineering and Radiation Oncology, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Ted A
authors.initials: TA
authors.lastname: Bateman
authors.affiliation: Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Marc S
authors.initials: MS
authors.lastname: Mendonca
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Khalid S
authors.initials: KS
authors.lastname: Mohammad
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Theresa A
authors.initials: TA
authors.lastname: Guise
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D001823:Body Composition; D001862:Bone Resorption / Q000473:pathology*; D001842:Bone and Bones / Q000473:pathology* / Q000528:radiation effects*; D004195:Disease Models, Animal; D004307:Dose-Response Relationship, Radiation; D006614:Hindlimb / Q000528:radiation effects*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010006:Osteoblasts / Q000378:metabolism / Q000528:radiation effects; D010012:Osteogenesis / Q000528:radiation effects; D000067996:RAW 264.7 Cells; D012886:Skull / Q000473:pathology / Q000528:radiation effects; D013997:Time Factors; D014965:X-Rays
keywords: MARROW ADIPOSITY; MICROARCHITECTURE; OSTEOBLAST; OSTEOCLASTS; OSTEOCYTE; RADIATION