title: Changes in bone turnover markers during 14-day 6 degrees head-down bed rest.
abstract: Osteoporosis caused by exposure to microgravity represents a serious clinical concern, but the mechanisms have yet to be fully elucidated. The present research aimed to elucidate the effects of microgravity environments on bone turnover, with a specific focus on changes in bone resorption markers such as type I collagen cross-linked N-telopeptides (NTx) and deoxypyridinoline (Dpyr), for which scant data are available regarding detailed time course. Methods using 6 degrees head-down bed rest were utilized to simulate a microgravity environment. Eleven adult male volunteers underwent 6 degrees head-down bed rest for 14 days; measurements were made of serum and urine Ca concentrations, in addition to osteocalcin (OC), bone alkaline phosphatase (ALP), NTx, and Dpyr as bone turnover markers. By the end of bed rest, concentrations of bone ALP had significantly increased, but OC displayed a tendency toward decrease. Concentrations of Dpyr significantly increased from day 6, remaining elevated until the end of bed rest. Concentrations of NTx significantly increased on day 13 and at the end of bed rest. Serum and urinary concentrations of Ca increased significantly at the end of bed rest. Bone ALP represents a relatively early marker of osteoblast differentiation at the matrix maturation phase and OC is a late marker in osteoblast differentiation at the calcification phase. The present results therefore suggest an absolute increase in bone resorption and normal or reduced bone formation, together causing prominent uncoupling and rapid bone loss after simulated microgravity. Moreover, the present results suggest that bone resorption is enhanced at an early stage of exposure to microgravity environments.
authors.affiliation: Department of Hygiene and Space Medicine, Nihon University School of Medicine, 30-1 Oyaguchi-kamimachi, 173-8610 Tokyo, Itabashi-ku, Japan.
authors.forename: Hyeteok
authors.initials: H
authors.lastname: Kim
authors.forename: Kenichi
authors.initials: K
authors.lastname: Iwasaki
authors.forename: Takeo
authors.initials: T
authors.lastname: Miyake
authors.forename: Tomoki
authors.initials: T
authors.lastname: Shiozawa
authors.forename: Sadahiko
authors.initials: S
authors.lastname: Nozaki
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Yajima
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000652:urine; D001510:Bed Rest / Q000009:adverse effects; D015415:Biomarkers / Q000032:analysis* / Q000097:blood / Q000652:urine; D016723:Bone Remodeling / Q000502:physiology; D001862:Bone Resorption / Q000097:blood / Q000378:metabolism* / Q000652:urine; D002118:Calcium / Q000097:blood / Q000652:urine; D003094:Collagen / Q000652:urine; D024042:Collagen Type I; D006801:Humans; D018476:Hypokinesia / Q000097:blood / Q000378:metabolism* / Q000652:urine; D008297:Male; D010455:Peptides / Q000652:urine; D013997:Time Factors; D014893:Weightlessness / Q000009:adverse effects*
chemical_list: D000596:Amino Acids; D015415:Biomarkers; D024042:Collagen Type I; D010455:Peptides; C052929:collagen type I trimeric cross-linked peptide; C036020:deoxypyridinoline; D003094:Collagen; D002118:Calcium