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Bone Mineral Density (BMD), Bone Mineral Content (BMC), and MMP-8 and MMP-9 Levels in Human Mandibular and Alveolar Bone: A Study in Simulated Microgravity
Exposure of astronauts and cosmonauts to microgravity conditions has been associated with several physiological changes including but not limited to 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 flights. However, to date there has been no study on the effects of mandibular bone and alveolar bone density loss in both sexes in a simulated microgravity environment. The current study was designed to determine bone mineral density (BMD) and GCF MMP-8 and MMP-9 levels in normal healthy subjects of both sexes in simulated microgravity conditions based on -6° head-down-tilt (HDT) bed rest. The subjects in this investigation were 10 male and 10 female volunteers participating in a three-week, 6° HDT bed-rest exposure. The BMD and Bone Mineral Content (BMC) of each individual were measured by dual energy X-ray absorptiometry before and during simulated microgravity. GCF MMP-8 and MMP-8 levels were measured by enzyme-linked immunosorbent assays. BMD and BMC levels were, in both genders, significantly <I>decreased</I> in simulated microgravity (although insignificantly a higher loss was observed in females as compared to males). In comparison, the MMP-8 and MMP-9 levels were significantly increased in simulated microgravity as compared to those in normal conditions (again insignificantly higher in females compared to males). Further studies are required using a larger sample size including all factors affected in simulated microgravity and true zero gravity.
Simulated Microgravity Condition, Head-down-tilt, Bone Loss, MMP-8, MMP-9, Bone Mineral Density (BMD), Bone Mineral Content (BMC)
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