Anabolic Effect of Insulin Therapy on the Bone: Osteoprotegerin and Osteocalcin Up-Regulation in Streptozotocin-Induced Diabetic Rats

Type 1 diabetes mellitus (T1DM) is associated with several skeletal alterations, particularly in conditions of poor glycaemic control. Insulin therapy is the major conservative treatment for T1DM; however, the effects of this hormone on bone markers of T1DM rats are limited, and the regulatory mechanisms remain elusive. Therefore, the evaluation of molecular and non-molecular parameters in a chronic animal model of T1DM-induced bone loss, treated with and without insulin, may help in elucidating the insulin mechanisms. Male Wistar rats were assigned into three groups: control, T1DM (T1DM rats induced with streptozotocin [STZ] at 40 mg/kg intravenously) and T1DM plus insulin therapy (T1DMI). After 8 weeks, we evaluated the serum biochemical, tibia histomorphometric and biomechanical parameters, as well as the gene expression of the receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG) and osteocalcin (OC) of femur mRNA. Compared with T1DM, the T1DMI group showed less bone loss, which was revealed by the increased trabecular width (TbWi, p < 0.001) and trabecular bone area (BAr, p < 0.01), reduced trabecular separation (TbSp, p < 0.01) and increased Young's modulus (p < 0.05). Moreover, molecular analyses indicated that the expression of OPG and OC was up-regulated (p < 0.001 and p < 0.05, respectively). In summary, the up-regulation of OPG and OC in the T1DMI group supports an anabolic effect of insulin, which was demonstrated by the maintenance of bone architecture and flexibility. These results suggest that insulin therapy may prevent T1DM-induced bone loss via the effects on the bone formation.