Abstract
OBJECTIVE: To establish a hypobaric hypoxia rat model in a real high-altitude environment, to investigate the effects of the real high-altitude environment on rat bone mass and bone microstructure using multiple methods such as Micro CT, blood biochemistry, and pathology, and to explore the potential mechanisms involved. METHODS: Sprague Dawley (SD) rats were transported to the Yushu Plateau Laboratory (at 4250 m above sea level) in Qinghai Province and kept there for 4, or 8, or 18 months. These groups were designated as H-4, H-8, and H-18, respectively. Upon completion of the high-altitude exposure, these animals were transported to the Molecular Imaging Laboratory, West China Hospital, Sichuan University (at 500 m above sea level) in Chengdu for relevant testing and comparison with the control animals raised in a low-altitude environment for the same durations (designated L-4, L-8, and L-18). The tests performed included blood biochemistry, Micro CT imaging, and pathological assessments such as ELISA, Western blot, and HE and TRAP staining. RESULTS: Compared with that of the control group, the body mass of rats in the H-4 and H-18 groups decreased significantly (H-4 group vs. L-4 group: [513.75±35.10] g vs. [649.18±60.03] g, P<0.01; H-18 group vs. L-18 group: [535.58±66.65] g vs. [670.86±44.96] g, P<0.01). The serum Ca(2+) concentration was higher in the H-8 group and H-18 group compared to that in the control group (H-8 group vs. L-8 group: [2.48±0.09] mmol/L vs. [2.38±0.07] mmol/L, P<0.05; H-18 group vs. L-18 group: [2.55±0.11] mmol/L vs. [2.13±0.27] mmol/L, P<0.05). No statistically significant difference was observed in the concentration of P(3+). Bone metabolism indicator cross-linked carboxy-terminal telopeptide of type Ⅰ collagen (CTX-Ⅰ) was significantly increased in all high-altitude groups compared to the low-altitude groups (H-4 group vs. L-4 group: [1.44±0.08] ng/mL vs. [0.70±0.13] ng/mL, P<0.01; H-8 group vs. L-8 group: [1.52±0.10] ng/mL vs. [0.75±0.10] ng/mL, P<0.01; H-18 group vs. L-18 group: [2.70±0.13] ng/mL vs. [1.94±0.15] ng/mL, P<0.01). In addition, CT results showed a decrease in bone volume fraction of trabecular bone in the three high-altitude groups (H-4 group vs. L-4 group: [7.48±2.35]% vs. [10.40±2.93]%, P<0.05; H-8 group vs. L-8 group: [7.17±2.68]% vs. [10.09±2.95]%, P<0.05; H-18 group vs. L-18 group: [2.90±2.91]% vs. [8.68±4.11]%, P<0.01), and increased trabecular separation in the three high-altitude groups (H-4 group vs. L-4 group: [0.70±0.12] mm vs. [0.60±0.06] mm, P<0.05; H-8 group vs. L-8 group: [0.68±0.07] mm vs. [0.59±0.05] mm, P<0.01; H-18 group vs. L-18 group: [0.80±0.09] mm vs. [0.70±0.09] mm, P<0.05). TRAP staining showed an increase in osteoclasts in the H-4 and H-18 groups. Western blot results indicated an increase in the expression of receptor activator of nuclear factor-κB ligand (RANKL) and hypoxia inducible factor-1α (HIF-1α) in high-altitude environment, while the expression of osteoprotegerin (OPG) was inhibited. CONCLUSION: The impact of high-altitude environment on rat femurs is characterized primarily by a reduction in trabecular bone mass and damage to bone microstructure.