Osteoporosis in a Rat Model Co-Exposed to Cigarette Smoke and Intermittent Hypoxia

Purpose: There are few studies on osteoporosis in chronic obstructive pulmonary disease-obstructive sleep apnea overlap syndrome, and the results obtained are inconsistent. The purpose of our study is to observe the occurrence of osteoporosis and its possible mechanism in rat model co-exposed to cigarette smoke and intermittent hypoxia.

Materials and methods: The rats were randomly divided into four groups: air exposed group, cigarette smoke (CS) exposed group, 10% concentration of intermittent hypoxia exposed group, CS combined with 10% concentration of intermittent hypoxia exposed group. All animals completed lung function and lung tissue morphology assessment. The femurs were examined by microcomputer tomography (microCT). Tartrate-resistant acidic phosphatase (TRAP) staining was used to evaluate the osteoclasts. We also assessed the interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in peripheral blood.

Results: There was no difference in the femoral length between each group, but the quantitative analyses of microCT showed that compared with the air exposed group, the percent bone volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), cortical thickness (Ct.Th) and bone mineral density (BMD) decreased, and the trabecular separation (Tb.Sp) and the proportion of trap-positive cells increased significantly in the overlapping exposed group. There were higher levels of BV/TV in the overlapping group than CS exposed group. Compared with the intermittent hypoxia exposed group, there were lower levels of Tb.Th and Ct.Th and higher levels of Tb.Sp in the overlapping exposed group. However, there was no statistical difference of trap-positive cell between the overlapping exposed group and the CS exposed single group or the intermittent hypoxia exposed group. There were higher levels of IL-6 and TNF-α in the overlapping exposed group than those in the air-exposed group.

Conclusion: Bone destruction increased in the overlapping exposed rat model compared with the rat exposed to air, which may be related to the upregulation of inflammation.