直立体位下无创轴向加载建立兔椎间盘退变动物模型

Upright posture combined with noninvasive axial loading-induced rabbit intervertebral disc degeneration

中文关键词:  椎间盘退变  动物模型  轴向载荷  无创性  兔

英文关键词:Intervertebral disc degeneration  Animal model  Axial load  Noninvasive  Rabbit

中文摘要:

  【摘要】 目的：通过直立体位下无创性轴向加载的方式，建立一种新型兔腰椎间盘早期退变的动物模型。方法：24只4月龄雄性新西兰大白兔随机分为实验组及对照组。将实验组动物置于特制筒内使之保持直立体位，并自颈部施以600g轴向载荷，每日6h；对照组动物不接受任何处理而常规饲养。在实验开始前及实验开始后4周、8周、12周时对全部动物行X线及MRI检查，观察实验组动物在筒内时腰椎的骨性结构，通过椎间盘高度指数（disc height index，DHI）测量，比较两组动物侧卧位时L2/3、L4/5和L6/7节段椎间隙高度改变；通过髓核相对灰度值测量比较两组动物髓核含水量变化。14周后全部动物处死，取L5/6节段胶冻状髓核组织，应用rt-PCR检测Ⅰ型胶原、Ⅱ型胶原及蛋白多糖表达水平；取L6/7节段椎间盘连同上、下各1mm软骨下骨，应用HE及天狼星红染色观察各组动物椎间盘组织结构改变。结果：2只实验组动物在实验过程中死亡，其对应的实验数据从结果中剔除。腰椎X线片显示，在直立体位负重条件下，实验组兔腰椎形成明显后凸，较侧卧位下腰椎间隙明显变窄，在L2/3节段，直立体位下椎间隙高度为侧卧位时的75.1%（P<0.05）；在L4/5节段为54.8%（P<0.05）；在L6/7节段为47.9%（P<0.05）。DHI测量显示两组动物腰椎各节段DHI在任何时间点均无显著差异（P>0.05）。MRI结果显示，在L2/3节段，实验组与对照组髓核灰度值在任何时间点均无统计学差异（P>0.05），在L4/5节段，实验组与对照组髓核相对灰度值在12周时开始具有显著差异（P<0.05）；在L6/7节段，两组间在8周时即开始有显著性差异（P<0.05）。rt-PCR结果显示，实验组Ⅰ型胶原mRNA表达明显高于对照组（3.57倍，P<0.05）；而Ⅱ型胶原及蛋白多糖表达明显低于对照组（分别为0.35倍和0.43倍，P<0.05）。病理学检查显示对照组与实验组椎间盘组织结构存在显著差异，对照组髓核组织与纤维环间边界清晰，髓核内富含均匀分布的髓核细胞；实验组内层纤维环明显增生，而髓核区域相应减小。结论：直立体位下无创性轴向加载方式可显著加速兔腰椎间盘的退变进程，其在发病机理上与人类椎间盘退变更加相似，该腰椎间盘退变动物模型操作简单、可重复性强。

英文摘要:

  【Abstract】 Objectives: To establish a novel in vivo rabbit model of early intervertebral disc degeneration(IDD) that can better simulate the IDD process in humans. Methods: 24 four-month-old male New Zealand white rabbits were randomly assigned into two groups(experimental group and control group). Each rabbit in the experimental group(n=12) was placed into a plastic tube specially designed to maintain the animal in an upright posture. A collar weighed 600g was placed onto the neck of each experimental rabbit, 6 hours for one day. Rabbits in the control group(n=12) were regularly fed in their cages throughout the experiment. Before the experiment and at 4, 8 and 12 weeks after the experiment, lumbar lateral radiographs and MRI were taken in the lateral decubitus position for both the experimental group and the control group to monitor the signs of disc degeneration by measuring disc height index(DHI) and grayscale values of nucleus pulposus(NP). At 14 weeks, all animals in both groups were sacrificed. The NPs of L5/6 were obtained for quantitative real time-PCR(rt-PCR) analysis. Disc segment L6/7 was obtained for histologic analysis. The specimens were cut midsagittally and stained with hematoxylin and eosin(H&E) and picrosirius red. Results: Two rabbits in the experimental group died during the study, and their data were not included in the final results. The lateral radiograph of rabbits in the experimental group which had been placed into the tube and maintained in an upright position showed that there was an obvious kyphotic curvature on the lower lumbar spine, and the disc height of L2/3, L4/5 and L6/7 was much smaller than the height in the image of the same rabbit in lateral decubitus position, 75.1%, 54.8% and 47.9% respectively for each segment(all P<0.05). DHI measurement showed no significant difference between two groups at any time point. Serial MRI scans showed that animals in the experimental group presented a progressive decrease in the signal intensity of their lumbar discs over the 14-week period. In contrast, NP signal intensities in the control group decreased more slowly during the same period. Significant differences between two groups were observed since 12 weeks in L4/5(P<0.05) and 8 weeks in L6/7(P<0.05). The result of rt-PCR showed that the collagen type Ⅰ mRNA expressions were significantly greater(3.06-fold), whereas collagen type Ⅱ and aggrecan mRNA expressions were significantly less(0.35-fold and 0.37-fold respectively) in the experimental group than those in the control group(all P<0.05). Histologic examination showed significant difference between the control and experimental group. In the experimental group, there was a large increase in fibrocartilage lamellas in the inner border of posterior AF, resulting in a significantly decreased gelatinous NP area. Conclusions: The upright posture combined with noninvasive external loading method can induce accelerated degenerative changes in rabbit lumbar discs. These mild degenerative changes closely resemble those which occur in the early phase of disc degeneration in humans, which suggest its use in future studies.