ALBERT

Description: No abstract available

Description: Spaceflight is a potential risk factor for secondary osteoporosis in astronauts. Although lumbar spine (LS) BMD declines rapidly, more than expected for age, there have been no fragility fractures in astronauts that can clearly be attributed to spaceflight. Recently, astronauts have been returning from 6month spaceflights with absolute BMD still above young adult mean BMD. In spite of these BMD measurements, we project that the rapid loss in bone mass over longduration spaceflight affects the bone microarchitecture of the LS which might predispose astronauts to premature vertebral fractures. Thus, we evaluated TBS, a novel texture index correlated with vertebral bone microarchitecture, as a means of monitoring changes to bone microarchitecture in astronauts as they age. We previously reported that TBS detects an effect of spaceflight (~6month duration), independent of BMD, in 51 astronauts (47+/4 y) (Smith et al, J Clin Densitometry 2014). Hence, TBS was evaluated in serial DXA scans (Hologic Discovery W) conducted triennially in all active and retired astronauts and more frequently (before spaceflight, after spaceflight and until recovery) in the subset of astronauts flying 46 month missions. We used nonlinear models to describe trends in observations (BMD or TBS) plotted as a function of astronaut age. We fitted 1175 observations of 311 astronauts, preflight and then postflight starting 3 years after landing or after astronaut's BMD for LS was restored to within 2% of preflight BMD. Observations were then grouped and defined as follows: 1) LD: after exposure to at least one longduration spaceflight 〉 100 days and 2) SD: before LD and after exposure to at least one short-duration spaceflight 〈 30 days. Data from males and females were analyzed separately. Models of SD observations revealed that TBS and BMD had similar curvilinear declines with age for both male and female astronauts. However, models of LD observations showed TBS declining with age while BMD appeared stable or trending upward. For females (n=8) LD observations were too few to discern a trend. Notably, models describing trends in TBS appeared to be more sensitive to the effects of age than the models for BMD. We conclude that TBS may provide an additional index for the lumbar spine to monitor the combined changes due to spaceflight and due to aging. This increased knowledge may enhance the ability to identify an intervention trigger for premature vertebral fractures in astronauts.

Description: Bone loss due to longduration spaceflight has been characterized by both DXA and QCT serial scans. It is unclear if these spaceflightinduced changes in bone mineral density (BMD) and structure result in increased fracture incidence. NASA astronauts currently fly 5 to 6month missions on the International Space Station (ISS) and at least one 12month mission is planned. While NASA has measured areal BMD (by DXA) and volumetric BMD (by QCT) and has estimated hip strength (by finite element models of QCT data, no method has yet been used to examine bone microarchitecture from lumbar spine (LS). DXA scans are routinely performed pre and postflight on all ISS astronauts to follow BMD changes associated with spaceflight. Trabecular Bone Score (TBS) is a relatively new method that measures greyscalelevel texture information extracted from LS DXA images and correlates with 3D parameters of bone microarchitecture. We evaluated the ability of LS TBS to discriminate changes in astronauts who have flown on ISS missions and to determine if TBS can provide additional information compared to DXA. Methods: Lumbar Spine (L14) DXA scans from 51 astronauts (mean age, 47 +/- 4 yrs) were divided into 3 groups based on the exercise regimens performed onboard the ISS. "PreARED" (exercise using a loadlimited resistive exercise device, 〈300 lb), "ARED" (exercise with a highload resistive exercise device, up to 600 lb) and "Bisphos+ARED" group (ARED exercise and a 70mg alendronate tablet once a week before and during flight, starting 17 days before launch). DXA scans were performed and analyzed on a Hologic Discovery W using the same technician for the pre and postflight scans. LSC for the LS in our laboratory is 0.025 g/sq. cm. TBS was performed at the Mercy Hospital, Cincinnati, Ohio on a similar Hologic computer. Data were analyzed using a paired, 2tailed Student's ttest for the difference between pre and postflight means. Percent change and % change per month are noted. Interpretation: Our data suggest that: TBS and DXA both detected significant decrements in the LS in these pre ARED astronauts, not unexpected given the insufficient loads provided by this early exercise device. TBS did not detect significant changes in the ARED or Bisphos+ARED groups while DXA did detect significant changes in the ARED astronauts. These findings suggest that DXA and TBS are detecting independent effects of bone loss interventions tested in ISS astronauts in space, which may be due to distinct effects of interventions on mineral content of separate cortical vs. trabecular bone. Conclusion: TBS, in conjunction with DXA BMD, may provide additional insight into the nature of changes (or lack thereof) in the microstructure of trabecular bone and the areal BMD of vertebral bodies.