Department of Biomedical Engineering, City College of New York, New York, NY 10031, USA.
Research Division, Hospital for Special Surgery, New York, NY 10021, USA.
Bone. 2014 Feb;59:229-34. doi: 10.1016/j.bone.2013.11.026. Epub 2013 Dec 4.
To test if osteoporosis alters mechanical load-induced interstitial fluid flow in bone, this study examined the combined effect of estrogen deficiency and external loading on solute transport around osteocytes. An in vivo tracer, FITC-labeled bovine serum albumin, was injected into anesthetized ovariectomized and control female Sprague-Dawley rats before the right tibia was subjected to a controlled, physiological, non-invasive sinusoidal load to mimic walking. Tracer movement through the lacunar-canalicular system surrounding osteocytes was quantified in cortical and cancellous bone from the proximal tibia using confocal microscopy, with the non-loaded tibia serving as internal control. Overall, the application of mechanical loading increased the percentage of osteocyte lacunae labeled with injected tracer, and ovariectomy further enhanced movement of tracer. An analysis of separate regions demonstrated that ovariectomy enhanced in vivo transport of the injected tracer in the cancellous bone of the tibial epiphysis and metaphysis but not in the cortical bone of the metaphysis. These findings show that bone changes due to reduced estrogen levels alter convectional transport around osteocytes in cancellous bone and demonstrate a functional difference of interstitial fluid flow around osteocytes in estrogen-deficient rats undergoing the same physical activity as controls. The altered interstitial fluid flow around osteocytes is likely related to nanostructural matrix-mineral level differences recently demonstrated at the lacunar-canalicular surface of estrogen-deficient rats, which could affect the transmission of mechanical loads to the osteocyte.
为了测试骨质疏松是否改变了骨内机械负荷诱导的细胞外液流动，本研究探讨了雌激素缺乏和外部加载对破骨细胞周围溶质运输的综合影响。在麻醉的去卵巢和对照雌性 Sprague-Dawley 大鼠中，将 FITC 标记的牛血清白蛋白示踪剂注入右侧胫骨之前，对胫骨进行了受控的、生理的、非侵入性的正弦波加载，以模拟行走。使用共聚焦显微镜，从胫骨近端的皮质骨和松质骨中定量分析示踪剂在围绕破骨细胞的骨陷窝-骨小管系统中的运动，未加载的胫骨作为内部对照。总体而言，机械加载增加了用注射示踪剂标记的破骨细胞腔隙的百分比，去卵巢进一步增强了示踪剂的运动。对单独区域的分析表明，去卵巢增强了胫骨骺和骨干的松质骨中注射示踪剂的体内转运，但在骨干皮质骨中没有增强。这些发现表明，由于雌激素水平降低导致的骨变化改变了松质骨中破骨细胞周围的对流性转运，并证明了在接受与对照相同的体育活动的去势大鼠中，破骨细胞周围细胞外液流动存在功能差异。破骨细胞周围细胞外液流动的改变可能与最近在去势大鼠的骨陷窝-骨小管表面显示的纳米结构基质-矿物质水平差异有关，这可能影响机械负荷向破骨细胞的传递。
