Effects of activated vitamin D, alfacalcidol, and low-intensity aerobic exercise on osteopenia and muscle atrophy in type 2 diabetes mellitus model rats

Diabetes mellitus causes secondary osteoporosis and muscle atrophy. The ability of alfacalcidol (ALF) and exercise (Exe) to inhibit osteoporosis and muscle atrophy in type 2 diabetes mellitus (T2DM) model rats was examined. Twenty-week-old Otsuka Long-Evans Tokushima Fatty rats were randomized to ALF (orally 0.1 μg/kg/day), Exe (treadmill exercise at 10 m/min, 60 min/day, 5 days/week), Comb (ALF and Exe), and Cont (T2DM control treated with vehicle and no exercise) groups (n = 8–10 per group). Sedentary Long-Evans Tokushima Otsuka rats were used as a non-hyperphagic control. After treatment for 2 or 6 weeks, blood glucose (BG) levels, cross-sectional area (CSA) of tibialis anterior muscle fibers, femoral bone mineral density (BMD), and relative quantities of muscle anabolic markers (Pax7, MyoD, and myogenin) and catabolic markers (Atrogin-1, MuRF1, and REDD1) of the soleus muscle assessed by real-time polymerase chain reaction assays were measured. Exe and Comb treatments for 6 weeks decreased BG levels compared with those of the Cont group. ALF, Exe, and Comb treatments for 2 and 6 weeks recovered the CSA compared with that of the Cont group. ALF and Comb treatments for 6 weeks increased femoral BMDs compared with those of the Cont group. After 2 weeks of treatment, Comb treatment increased MyoD expression and decreased MuRF1 expression. ALF or Exe monotherapy significantly decreased Atrogin-1 or MuRF1 expression after 2 weeks of treatment, respectively. After 6 weeks of treatment, ALF and Comb treatments decreased Atrogin-1 and REDD1. These results demonstrate that a combination of ALF and Exe improved CSA from the early phase of treatment by stimulating skeletal muscle differentiation and suppressing muscle catabolic genes. Improvements in BG, BMD, and CSA were observed as long-term effects of the combination therapy. Continued suppression of muscle catabolic genes was observed as a background to these effects.

糖尿病可引发继发性骨质疏松与肌肉萎缩。本研究旨在考察阿法骨化醇（alfacalcidol, ALF）与运动疗法（exercise, Exe）对2型糖尿病（type 2 diabetes mellitus, T2DM）模型大鼠骨质疏松及肌肉萎缩的抑制作用。选取20周龄的Otsuka Long-Evans Tokushima肥胖大鼠，随机分为ALF组（每日口服0.1μg/kg）、运动组（以10m/min速度进行跑台运动，每日60分钟，每周5天）、联合组（ALF联合运动，Comb）与T2DM模型对照组（Cont，给予溶剂处理且无运动），每组8~10只；另以久坐型Long-Evans Tokushima Otsuka大鼠作为非多食性对照组。分别于干预2周或6周后，检测各组大鼠的血糖（blood glucose, BG）水平、胫骨前肌肌纤维横截面积（cross-sectional area, CSA）、股骨骨密度（femoral bone mineral density, BMD），并通过实时聚合酶链反应检测比目鱼肌中肌肉合成代谢标志物（Pax7、MyoD及肌细胞生成素myogenin）与分解代谢标志物（Atrogin-1、MuRF1及REDD1）的相对表达量。干预6周后，运动组与联合组的血糖水平较模型对照组显著降低；干预2周和6周后，ALF组、运动组及联合组的肌纤维横截面积均较模型对照组得以恢复；干预6周后，ALF组与联合组的股骨骨密度较模型对照组显著升高。干预2周后，联合组可上调MyoD表达并下调MuRF1表达；ALF单一疗法与运动单一疗法分别可在干预2周后显著降低Atrogin-1与MuRF1的表达。干预6周后，ALF组与联合组可下调Atrogin-1与REDD1的表达。本研究结果表明，ALF联合运动可通过刺激骨骼肌分化、抑制肌肉分解代谢基因表达，从干预早期便改善肌纤维横截面积；联合疗法的长期效应可改善血糖水平、股骨骨密度与肌纤维横截面积，而持续抑制肌肉分解代谢基因表达是上述效应的重要基础。