Determinants of Femur and Tibia Fragility in Diabetes Using Dexamethasone-Induced Insulin Resistance in Rats

Type 2 diabetes, mainly driven by insulin resistance (IR), represents 90% of diabetic cases and has been related to bone fragility and fractures. However, it is unclear how hyperglycaemia, IR and oxidative stress interplay to induce bone fragility. This study was then undertaken to examine the contribution and the interconnection of hyperglycaemia, insulinopenia, IR and oxidative stress to bone fragility, as well as the time- and severity-dependent effects of insulin impairment on bone fragility and its reversibility. IR was induced by dexamethasone in three different protocols: 1 mg/kg/day/im for 7 consecutive days; 500 μg/kg/day/im for 7 consecutive days, the dose was changed to 100 μg/kg/day/im for the following 14 days; and 200 μg/kg/day/im for 21 consecutive days. Fasting glycaemia, glucose tolerance test (GTT) and insulin tolerance test (ITT) were performed at the end of each treatment period while body mass was recorded daily. A control group receiving DMSO 4% was constituted for each protocol. Following euthanasia, the serum was collected for lipid profile, calcium, phosphate and alkaline phosphatase. The pancreas and liver were collected for the assessment of oxidative stress markers. Tibia and femur were collected to assess calcium phosphate and histological modifications. Dexamethasone induced an increase in baseline blood glucose and insulin intolerance while promoting glucose tolerance. A decrease in animal body weight as well as disturbances in oxidative stress, calcium and lipid profiles were observed in dexamethasone-treated animals. Bone histopathology showed loss of bone matrix, decreased collagen and an increase in Trap expression in dexamethasone-treated rats. Bone alterations were positively correlated with oxidative stress and IR. These results show that the phosphocalcic metabolism disruption and bone structure alterations induced by glucocorticoids are related to IR (time and severity) and oxidative stress status. Surprisingly, the relation is more effective on the tibia than the femur.