骨髓脂肪细胞在激素性骨坏死发生过程中的时序变化特点

The temporal change of bone marrow fat cells in the process of steroid-associated osteonecrosis development

目的血管外脂肪堆积如何参与激素性骨坏死的发病机制目前仍然不清楚。本课题应用建立的激素性骨坏死家兔模型研究骨髓脂肪细胞在骨坏死发生过程中组织病理形态学上的时序变化特点。方法32只28-32周龄成年新西兰大白兔分为正常对照组（n=16）和激素处理组（n=16）。激素处理组动物接受1次耳静脉内毒素注射和连续3次肌内糖皮质激素注射诱导骨坏死,正常对照组注射相应剂量的生理盐水。各组动物在最后一次注射糖皮质激素2周（早期）和4周（晚期）以后分别处死8只动物,获取双侧近端股骨,应用组织形态计量学技术分别测定股骨髓内脂肪细胞密度、脂肪细胞直径和脂肪细胞面积,同时进行骨坏死的组织病理学评价。结果激素处理早期组和晚期组骨髓脂肪细胞密度分别明显高于正常对照组67.1%和54.4%,但是早期组与晚期组之间差异不显著。激素处理晚期组骨髓脂肪细胞直径明显高于正常对照组,但是早期组骨髓脂肪细胞直径与正常对照组比较有减小趋势;激素处理早期组和晚期组骨髓脂肪细胞面积都分别明显高于正常对照组44%和83.6%,且晚期组亦显著高于早期组;脂肪细胞直径的频数分布显示,正常对照组峰值介于40-50μm,激素处理早期组较正常对照组增多的脂肪细胞直径介于30-40μm,晚期组较正常对照组增多的脂肪细胞直径介于50-60μm。组织病理学评价显示早期组骨坏死发生率为25%（2/8）,晚期组骨坏死发生率为87.5%（7/8）。结论在激素性骨坏死发生过程中,早期血管外脂肪堆积表现为大量生成的小脂肪细胞,后期血管外脂肪堆积表现为脂肪细胞出现肥大。

Objective How does the extravascular fat deposition contribute to the steroid-associated osteonecrcosis （ON） development still remains unclear. This study aimed to explore the time course change of bone marrow fat cells histopathologically based on our established ON model. Methods Thirty-two adult rabbits were divided into normal control group （ n = 16） and steroid-treatment group （ n = 16）. The rabbits in steroid-treatment group were injected with once lipopolysaccharide and three times of methylprednisolone to induce ON. The rabbits in the normal control group were injected with 0.9% normal saline accordingly. And they were sacrificed in week 2 （ n = 8） and week 4 （ n = 8） after steroid administration respectively. The bilateral femora were harvested and processed for bone marrow fat cell density, fat cell diameter and fat cells area percentage analysis histomorphometrically, and the ON incidence was also evaluated histopathologically. Results The fat cells density in steroid-treatment early and late group increased by 67.1% and 54.4% than the normal control group, but there was no significant difference between the treatment-early and -late groups; The fat cells diameter in late group was much larger than the control group, but the fat cell diameter in the early group was smaller than the control group; The fat cells area percentage in the early and late group increased by 44% and 83.6% than the control group. The fat cells size frequency profile showed most of the increased fat cells were small-sized cells ranging from 30 to 40 μm in diameter in the early group, but the large-sized cells ranging from 50 to 60μm in the late group. Conclusion The marrow fat cells featured increase in the number of small-sized fat cells in the early stage and enlargement in the size of fat cells in the late stage in steroid-associated ON development. These results indicate the active adipogenesis in the early stage and excessive lipogenesis in the late stage.