title: Bone mineral density, bone mineral content, gingival crevicular fluid (matrix metalloproteinases, cathepsin K, osteocalcin), and salivary and serum osteocalcin levels in human mandible and alveolar bone under conditions of simulated microgravity.
abstract: In astronauts and cosmonauts, exposure to microgravity has been associated with several physiological changes, including an osteoporosis like loss of bone mass. It has been reported that head-down tilt bed-rest studies mimic many of the observations seen in space flights. There has been no study of the effects of mandibular bone and alveolar bone loss in both sexes under conditions of simulated microgravity. This study was designed to investigate bone mineral density; bone mineral content; matrix metalloproteinase (MMP)-8, MMP-9, cathepsin K, and osteocalcin levels in gingival crevicular fluid (GCF); and salivary and serum osteocalcin levels in normal healthy men and women under conditions of simulated microgravity, namely, -6° head-down-tilt (HDT) bed rest. The subjects of this investigation were 10 male and 10 female volunteers who were exposed to 3 weeks of -6° HDT bed rest. Dual-energy X-ray absorptiometry was used to measure bone density and bone mineral content in alveolar bone from the mandibular canine to the third molar, as well as in the mandibular ramus, before, during, and after exposure to conditions of simulated microgravity. GCF (ie, MMP-8, MMP-9, cathepsin K, and osteocalcin) and salivary and serum osteocalcin levels were measured by enzyme-linked immunosorbent assays. Bone mineral density and bone mineral content were significantly lower under conditions of simulated microgravity in both sexes. The decreases were greater in women than in men, but the differences between sexes were not significant. Cathepsin, osteocalcin, MMP-8, and MMP-9 levels were significantly higher under conditions of simulated microgravity than under normal conditions; the increases were greater in women than in men, but the differences were not significant. Additional, more comprehensive, studies with larger sample sizes are now necessary for the investigation of simulated microgravity and microgravity.
authors.affiliation: Oral Imaging Center, School of Dentistry, Oral Pathology and Maxillofacial Surgery, Catholic University Leuven, Leuven, Belgium. raibalwant29@gmail.com
authors.forename: Balwant
authors.initials: B
authors.lastname: Rai
authors.forename: Jasdeep
authors.initials: J
authors.lastname: Kaur
authors.forename: Maria
authors.initials: M
authors.lastname: Catalina
mesh_terms: D000293:Adolescent; D000328:Adult; D016301:Alveolar Bone Loss / Q000209:etiology* / Q000517:prevention & control; D000539:Alveolar Process / Q000378:metabolism*; D015519:Bone Density; D056657:Cathepsin K / Q000032:analysis / Q000378:metabolism; D005260:Female; D005883:Gingival Crevicular Fluid / Q000737:chemistry / Q000201:enzymology; D018475:Head-Down Tilt / Q000009:adverse effects; D006801:Humans; D008297:Male; D008334:Mandible / Q000378:metabolism; D020784:Matrix Metalloproteinase 8 / Q000032:analysis / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000032:analysis / Q000378:metabolism; D015675:Osteocalcin / Q000032:analysis / Q000097:blood / Q000378:metabolism; D012471:Salivary Proteins and Peptides / Q000032:analysis / Q000378:metabolism; D012737:Sex Factors; D018474:Weightlessness Simulation / Q000009:adverse effects*; D055815:Young Adult
chemical_list: D012471:Salivary Proteins and Peptides; D015675:Osteocalcin; D056657:Cathepsin K; D020784:Matrix Metalloproteinase 8; D020780:Matrix Metalloproteinase 9