Effects of early and late treatments of low-intensity, high-frequency mechanical vibration on bone parameters in rats

Abstract

Low-intensity, high-frequency mechanical vibration (LHMV) has shown to increase bone formation. However, studies comparing the effectiveness of early- and late-treatments of LHMV to counteract bone loss have not been documented. This study was designed to compare the effects of early- and late-treatments of LHMV (at 30 Hz/0.6 g, 20 min per day/five days per week, for 12 weeks) on bone parameters in ovariectomized (Ovx) rats. Thirty days after ovariectomy, 40 adult rats were randomly divided into four groups: GI (early control group); GII treated with LHMV 3 weeks after Ovx (early treatment); GIII (late control group) and GIV treated with LHMV twelve weeks after Ovx (late treatment). Bone mineral density (BMD) was analyzed before Ovx and after treatments. Then, animals were killed, and the femurs were collected and their length and diaphysis diameter were measured; the distal femurs were taken and processed for histomorphometry and polarized light microscopy for collagen fibers analysis or subjected to immunohistochemistry of cleaved caspase-3 in osteocytes. Statistical analysis was done by ANOVA followed by the Bonferroni post hoc test (p < 0.05). BMD was similar among the groups before Ovx, but after treatments, it was significantly higher in GII and GIV compared with their control groups (p < 0.05). Femur length and cortical bone thickness were similar among the groups, but the diaphysis diameter of GII was higher compared with GI. Trabecular bone area was higher in the vibrated groups, but it was greater in GII (p < 0.05). Also, the vibrated groups showed the higher content collagen fibers and lower presence apoptotic osteocytes (positive caspase-3 immunoreactivity) when compared with the other groups (p < 0.05). These results suggest that both early- and late-treatments with LHMV counteract bone loss, being the early treatment more effective than the late treatment.

Chinese abstract

低强度、高频度机械振动（LHMV）可提升骨构造。然而，尚无关于LHMV早期治疗和晚期治疗，在抵抗骨丢失方面的有效性比较研究。本实验旨在比较LHMV早期和晚期治疗（30Hz/0.6g，每天20分钟，每周5次，共持续12周），在卵巢切除（Ovx）的大鼠中，骨参数方面的治疗效果。在卵巢切除后的30天，40只成年大鼠被随机分为4组：G1（早期对照组）；GII组在Ovx后3周开始LHMV（早期治疗）；GIII（晚期对照组）和GIV组在Ovx后12周开始LHMV。在Ovx前和治疗后测定骨密度（BMD）。接着，处死所有大鼠，收集它们的股骨，测量长度和骨干直径，并通过组织形态测定和和偏振光显微术，进行胶原蛋白的分析或者免疫组化法检测骨细胞中裂解半胱氨酸天冬氨酸蛋白酶-3水平。应用ANOVA的Bonferroni 事后检验方法进行数据分析（p<0.05）。在Ovx前BMD相似，但是在治疗之后，GII和GIV组含量明显升高，高于对照组（p<0.05）。股骨长度和皮质骨厚度在各组相似，但是GII组骨干直径高于GI组。骨小梁面积在振动组较高，在GII组更高（p<0.05）。与其它各组相比，振动组同样显示了较高的胶原纤维含量和较低的骨细胞凋亡情况（半胱氨酸天冬氨酸蛋白酶-3免疫反应阳性）（p<0.05）。这些结果说明早期和晚期LHMV治疗可以抵抗骨流失，早期治疗其效果优于晚期治疗效果。

Keywords:

• Bone histomorphometry
• DXA
• mechanical vibration and rats
• osteoporosis

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Acknowledgements

The authors wish to thank Dr Marise Lazaretti Castro (Professor of Endocrinology Department of UNIFESP/Brasil) for the X-ray absorptiometry (DXA) service. The authors especially wish to acknowledge Professor Dr. Eduardo Katchburian (in memorian).

Declaration of interest

The authors declare that they have no conflicts of interest.