Table 1.
Bone microstructural morphometry assessed by μCT in non-weight-bearing skeletal sites.
| Earth | Flight | |||
|---|---|---|---|---|
| Saline | TPO | Saline | TPO | |
| Calvarium | ||||
| TV (mm3) | 0.058 ± 0.003 | 0.058 ± 0.006 | 0.053 ± 0.005 | 0.053 ± 0.004 |
| BV (mm3) | 0.054 ± 0.003 | 0.054 ± 0.003 | 0.053 ± 0.005 | 0.051 ± 0.004 |
| BV/TV (%) | 94.496 ± 2.709# | 93.831 ± 3.501 | 99.370 ± 0.116b | 97.406 ± 1.267a,b’ |
| MV (mm3) | 0.003 ± 0.002# | 0.004 ± 0.002 | 0.0003 ± 0.00007b | 0.001 ± 0.001a |
| Width (mm) | 0.166 ± 0.008 | 0.166 ± 0.017 | 0.155 ± 0.012 | 0.152 ± 0.011 |
| Ct.Th (mm) | 0.096 ± 0.008# | 0.093 ± 0.010 | 0.117 ± 0.100b | 0.101 ± 0.002a |
| Tb.Th (mm) | 0.075 ± 0.006# | 0.073 ± 0.008 | 0.090 ± 0.006b | 0.079 ± 0.002a |
| Tb.Sp (mm) | 0.004 ± 0.002# | 0.005 ± 0.002 | 0.001 ± 0.0001b | 0.002 ± 0.001a,b’ |
| Tb.N (1/mm) | 12.690 ± 0.618# | 12.979 ± 0.910 | 11.024 ± 0.836b | 12.359 ± 0.296a |
| Mandible | ||||
| T.Ar (mm2) | 1.943 ± 0.020 | 1.923 ± 0.061 | 1.946 ± 0.045 | 1.914 ± 0.059 |
| B.Ar (mm2) | 1.311 ± 0.021 | 1.331 ± 0.055 | 1.337 ± 0.041 | 1.340 ± 0.051 |
| M.Ar (mm2) | 0.632 ± 0.041* | 0.592 ± 0.037 | 0.609 ± 0.029 | 0.574 ± 0.011a |
| B.Ar/T.Ar (%) | 67.498 ± 1.781 | 69.231 ± 1.715 | 68.719 ± ± 1.336 | 70.008 ± 0.578 |
| CEJ-ABC (mm) | 0.192 ± 0.008 | 0.213 ± 0.025 | 0.221 ± 0.027 | 0.221 ± 0.025 |
| Incisor | ||||
| T.Ar (mm2) | 0.467 ± 0.005 | 0.484 ± 0.022 | 0.481 ± 0.015 | 0.471 ± 0.010 |
| E + D.Ar (mm2) | 0.377 ± 0.034 | 0.421 ± 0.039 | 0.394 ± 0.037 | 0.380 ± 0.032 |
| Pu.Ar (mm2) | 0.090 ± 0.029 | 0.063 ± 0.018 | 0.087 ± 0.023 | 0.091 ± 0.028 |
| E + D.Ar/T.Ar (%) | 80.709 ± 6.539 | 86.857 ± 4.122 | 81.742 ± 5.355 | 80.593 ± 6.159 |
| Rib | ||||
| T.Ar (mm2) | 0.088 ± 0.024Ψ | 0.103 ± 0.012 | 0.114 ± 0.013b’ | 0.089 ± 0.014a |
| B.Ar (mm2) | 0.069 ± 0.017 | 0.075 ± 0.007 | 0.083 ± 0.008 | 0.069 ± 0.007a |
| M.Ar (mm2) | 0.019 ± 0.008Ψ | 0.028 ± 0.005 | 0.031 ± 0.005b’ | 0.020 ± 0.007a |
| B.Ar/T.Ar (%) | 78.766 ± 3.455Ψ | 72.787 ± 1.884a | 72.875 ± 2.140b | 77.601 ± 4.068a’,b’ |
| Ct.Th (mm) | 0.081 ± 0.006 | 0.079 ± 0.002 | 0.081 ± 0.002 | 0.081 ± 0.004 |
| Sternum | ||||
| TV (mm3) | 0.527 ± 0.029*’ | 0.512 ± 0.036 | 0.560 ± 0.045 | 0.518 ± 0.026 |
| BV (mm3) | 0.058 ± 0.012 | 0.045 ± 0.012 | 0.051 ± 0.006 | 0.050 ± 0.006 |
| BV/TV (%) | 10.994 ± 1.647Ψ | 8.796 ± 1.684a’ | 9.047 ± 0.751b | 9.724 ± 1.038 |
| BS/BV (%) | 0.084 ± 0.004 | 0.086 ± 0.006 | 0.088 ± 0.002b’ | 0.086 ± 0.006 |
| Tb.Th (mm) | 0.039 ± 0.002 | 0.040 ± 0.004 | 0.038 ± 0.001 | 0.040 ± 0.001a |
| Tb.Sp (mm) | 0.211 ± 0.017 | 0.243 ± 0.024a | 0.214 ± 0.022 | 0.212 ± 0.024 a,b’ |
| Tb.N (1/mm) | 2.770 ± 0.294*’,Ψ | 2.198 ± 0.337a | 2.380 ± 0.239b | 2.436 ± 0.273 |
| SMI | 1.718 ± 0.168* | 1.908 ± 0.140 | 1.774 ± 0.119 | 1.964 ± 0.301 |
| Conn.D (1/μm3) | 0.028 ± 0.008 | 0.020 ± 0.007 | 0.026 ± 0.005 | 0.028 ± 0.013 |
| Ct.Th (mm) | 0.081 ± 0.006 | 0.079 ± 0.002 | 0.081 ± 0.002 | 0.081 ± 0.004 |
Values are expressed as mean ± SD. TV tissue volume, BV bone volume, BV/TV bone volume fraction, MV marrow volume, calculated as TV−BV, Ct.Th average cortical thickness, Tb.Th trabecular thickness, Tb.Sp trabecular separation, Tb.N trabecular number, T.Ar tissue area, B.Ar bone area, M.Ar marrow area, calculated as T.Ar−B.Ar, B.Ar/T.Ar bone area fraction, CEJ-ABC lingual cementum–enamel to alveolar bone crest distance, E+D.Ar enamel + dentin area, Pu.Ar pulp area, E+D.Ar/T.Ar enamel + dentin area fraction, BS/BV specific bone surface, SMI structure model index, Conn.D connectivity density. Sample sizes for all bones are n = 5 unless otherwise indicated: Calvarium (TPO + Earth and Saline + Flight: n = 4), Mandible and Incisor (TPO + Earth: n = 4, TPO + Flight: n = 3), Rib (TPO + Earth: n = 3, TPO + Flight: n = 4). Significant interactions were detected by two-way ANOVA followed by Tukey post-hoc analyses and were designated by * when a significant main effect of TPO was detected (or a trend towards significance designated by *’ when p < 0.09); by # when a significant main effect of microgravity was detected; or by Ψ when a significant TPO × microgravity interaction was detected. Significant differences were also based on: (1) TPO treatment (e.g., TPO + Earth versus Saline + Earth or TPO + Flight versus Saline + Flight, designated by a when p < 0.05 indicating a significant difference or a’ when p < 0.09 indicating a trend towards significant difference); or (2) microgravity exposure with or without treatment (e.g., Saline + Earth versus Saline + Flight or TPO + Earth versus TPO + Fight, designated by b when p < 0.05 indicating a significant difference or b’ when p < 0.09 indicating a trend towards significant difference).