Table 2.
Biochemical markers of bone turnover and bone metabolism before, during and after spaceflight
| Pre-flight | FD15 | FD30 | FD60 | FD120 | FD180 | R+0 | |
| n† | 17 | 14 | 13 | 14 | 13 | 15 | 17 |
| Bone resorption | |||||||
| CTx (μg/d) | 1513 (1068, 1935) | 2845 (2047, 4126)** | 3009 (2587, 3427)** | 3669 (3083, 4708)** | 3231 (2609, 4065)** | 2768 (2335, 4108)** | 2834 (2108, 3909)** |
| CTx (μg/mmol Cr) | 91 (63, 135) | 139 (123, 178)** | 165 (131, 225)** | 191 (161, 226)** | 186 (137, 217)** | 163 (120, 244)** | 145 (112, 207)** |
| NTx (nmol/d) | 390 (323, 439) | 606 (461, 954)** | 589 (488, 702)** | 713 (531, 874)** | 600 (449, 905)** | 619 (479, 782)** | 651 (519, 740)** |
| NTx (nmol/mmol Cr) | 23 (20, 28) | 33 (22, 44)** | 32 (24, 40)** | 34 (28, 53)** | 31 (28, 41)** | 34 (27, 48)** | 38 (29, 45)** |
| Bone formation | |||||||
| BSAP (U/L) | 21.2 (18, 22.5) | 20.9 (19.2, 21.9) | 19.8 (18.1, 22.8) | 23.7 (20.5, 26.3) | 25.2 (22.6, 27.2)** | 26.9 (22.4, 31.2)** | 27 (23.6, 32.5)** |
| OC (ng/mL) | 20.9 (18.3, 23.6) | 20.3 (17.9, 26.4) | 22.6 (18.2, 27.2) | 24.6 (22.6, 28.9) ** | 29.9 (28.1, 36.1)** | 32.1 (29.4, 39.8)** | 26.6 (19.2, 28.7)** |
| P1NP (μg/L) | 48.8 (42.3, 57.1) | 46.3 (35.4, 58.4) | 51.2 (48.9, 58.8) | 75.1 (68.8, 82.1) ** | 99.5 (77.4, 109.8)** | 94.4 (74.8, 112.6)** | 83.0 (72.0, 100.5)** |
| Osteocyte activity | |||||||
| Sclerostin (pmol/L) | 26.2 (21.3, 31.3) | 31.0 (25.9, 35.6) | 29.7 (26.3, 36.9)** | 30.4 (25.7, 37.1)* | 31.5 (24.3, 35.1) | 26.9 (22.6, 33.5) | 28.7 (21.1, 31.9) |
| Regulators of bone metabolism | |||||||
| Urinary calcium (mmol/d) | 4.86 (4.20, 6.14) | 7.43 (5.20, 9.10)** | 5.63 (4.51, 6.50)* | 6.77 (6.08, 8.00)** | 6.64 (4.40, 7.39) | 5.06 (3.32, 6.21) | 6.56 (5.15, 7.73) |
| Serum calcium (mmol/L) | 2.30 (2.28, 2.35) | 2.38 (2.35, 2.45) | 2.40 (2.37, 2.42) | 2.35 (2.32, 2.40) | 2.35 (2.31, 2.41) | 2.35 (2.30, 2.45) | 2.27 (2.25, 2.40) |
| PTH (pg/mL) | 25.2 (22.1, 31.5) | 22.6 (18.0, 27.7) | 27.8 (21.3, 30.0) | 25.1 (17.0, 32.0) | 25.5 (19.0, 32.7) | 28.5 (22.0, 36.0) | 28.8 (25.5, 35.3) |
| 1,25(OH)2D (pmol/L) | 145 (128, 187) | 118 (102, 167) | 116 (96, 132)* | 133 (102, 160) | 130 (101, 162) | 137 (121, 171) | 185 (169, 232)* |
| 25OHD (nmol/L) | 86 (76, 96) | 82 (65, 86) | 77 (72, 87) | 81 (72, 86) | 79 (74, 85) | 80 (67, 84) | 77 (74, 81) |
| Phosphorus (mg/dL) | 3.8 (3.4, 4.0) | 4.0 (3.9, 4.1) | 4.3 (4.0, 4.7)* | 4.0 (3.7, 4.3) | 4.5 (3.8, 5.1)** | 4.2 (3.8, 4.6)* | 3.5 (3.2, 3.8) |
| OPG (pmol/L) | 4.7 (3.7, 5.2) | 4.5 (4.0, 4.9) | 4.5 (4.1, 5.3) | 4.7 (4.1, 5.2) | 4.8 (4.4, 5.1) | 4.5 (4.1, 5.3) | 4.7 (4.1, 5.6) |
| RANKL (pmol/L) | 217 (124, 312) | 198 (110, 304) | 222 (167, 318) | 171 (134, 273) | 183 (123, 296) | 207 (144, 317) | 140 (114, 287) |
| RANKL/OPG | 46 (31, 68) | 47 (29, 63) | 45 (37, 71) | 40 (30, 57) | 37 (29, 60) | 48 (28, 81) | 29 (20, 67) |
| Chemistry | |||||||
| 24 hours urine volume (mL) | 1741 (1475, 2062) | 1408 (1020, 1845) | 1302 (1156, 1775) | 1472 (1221, 2241) | 1291 (1130, 1922) | 1358 (1123, 2025) | 1921 (1602, 2549) |
| Urinary creatinine (mmol/d) | 17 (16, 18) | 20 (18, 21) | 20 (18, 23) | 20 (18, 21) | 19 (16, 21) | 20 (17, 24) | 18 (17, 19) |
| Serum creatinine (mg/dL) | 1.00 (0.90, 1.00) | 1.00 (0.90, 1.03) | 1.00 (0.90, 1.10) | 0.97 (0.87, 1.00) | 0.99 (0.90, 1.10) | 1.00 (0.88, 1.10) | 0.90 (0.78, 0.90)** |
Data are median (IQR).
*p<0.05; **p<0.01 compared with pre-flight (mean of L-180 and L-45) based on linear mixed effects model with small sample adjustment and Bonferroni correction. OC, 25OHD, RANKL and RANKL/OPG were log-transformed for analysis.
†Maximum sample size for data collection period. Three participants did not have CTx analysed at any timepoint.
BSAP, bone-specific alkaline phosphatase; CTx, type I collagen C-terminal cross-linked telopeptide; NTx, type I collagen N-terminal cross-linked telopeptide; OC, osteocalcin; 25OHD, 25-hydroxyvitamin D; 1,25(OH)2D, 1,25 di-hydroxyvitamin D; OPG, osteoprotegerin; P1NP, procollagen type 1 amino-terminal propeptide; PTH, intact parathyroid hormone.