Amylin and Bone Metabolism in Streptozotocin-Induced Diabetic Rats

Abstract

Amylin (AMY) is a 37 amino acid peptide cosecreted with insulin (INS) by pancreatic ␤-cells and absent in type 1 diabetes, a condition frequently associated with osteopenia. AMY binds to calcitonin receptors, lowers plasma calcium concentration, inhibits osteoclast activity, and stimulates osteoblasts. In the present study, we examined the effects of AMY replacement on bone loss in a streptozotocin (STZ)-induced rodent model type 1 diabetes. Of 50 male Wistar rats studied, 40 were made diabetic with intraperitoneal STZ (50 mg/kg; plasma glucose concentrations >11 mM within 5 days). Ten nondiabetic control (CONT) rats received citrate buffer without STZ. Diabetic rats were divided into four groups (n ‫؍‬ 10/group) and injected subcutaneously with rat AMY (45 mg/kg), INS (12 U/kg), both (same doses), or saline (STZ; diabetic controls) once per day. After 40 days of treatment and five 24-h periods of urine collection for deoxypyridinoline (DPD), the animals were killed, blood was sampled, and femurs were removed. The left femur was tested for mechanical resistance (three-point bending). The right femur was tested for total, diaphyseal (cortical bone), and metaphyseal (trabecular bone) bone densities using dual-energy X-ray absorptiometry (DXA). Bone was ashed to determine total bone mineral (calcium) content. None of the treatments had any significant effect on femoral length and diameter. Untreated diabetic rats (STZ; 145 ؎ 7N) had lower bone strength than did nondiabetic CONT (164 ؎ 38; p < 0.05). Total bone mineral density (BMD; g/cm 2 ) was significantly lower in STZ (0. 2523 ؎ 0. 0076) than in CONT (0.2826 ؎ 0.0055), as were metaphyseal and diaphyseal densities. Diabetic rats treated with AMY, INS, or both had bone strengths and bone densities that were indistinguishable from those in nondiabetic CONT. Changes in bone mineral content paralleled those for total BMD (T-BMD). Plasma osteocalcin (OC) concentration, a marker for osteoblastic activity, was markedly lower in untreated diabetic rats (7. 6 ؎ 0. 9 ng/ml); p < 0. 05) than in nondiabetic CONT (29. 8 ؎ 1. 7; p < 0. 05) or than in AMY (20. 1 ؎ 0. 7; p < 0. 05). Urinary DPD excretion, a marker for bone resorption, was similar in untreated and AMY-treated diabetic rats (

Decreased osteoclastogenesis, osteoblastogenesis and low bone mass in a mouse model of type 2 diabetes

“…Osteoblastogenesis assay. Bone marrow stromal cells were collected and seeded at a density of 2.5x10 5 /cm 2 in 24-well plates with osteoblast differentiation-inducing media containing α-Minimum Essential Media (α-MEM; Gibco-BRL, Carlsbad, CA, USA) supplemented with 15% fetal bovine serum (FBS; Gibco-BRL), 100 µM ascorbate phosphate, 5 M β-glycerol phosphate and 10 nM dexamethasone. The media were changed every 2 days.…”

“…Primary bone marrow cells were collected and seeded at a density of 2.5x10 5 /cm 2 in the presence of α-MEM (Gibco-BRL) supplemented with 15% FBS (Gibco-BRL). Floating, non-adherent cells were harvested after 24 h and seeded at a density of 2x10 5 /cm 2 into 48-well plates using medium supplemented with 50 ng/ml macrophage colony-stimulating factor and 50 ng/ml receptor activator of nuclear factor κ-B ligand (RANKL; R&D Systems, Minneapolis, MN, USA). The media were changed every 2 days.…”

“…A number of studies have reported that type 1 diabetes changes bone remodeling by impairing bone formation, leading to osteopenia (2,5). By contrast, bone loss in T2DM is less accepted, with reports of bone mineral density (BMD) ranging from low to high in T2DM (6)(7)(8).…”

Osteogenic Protein-1 Overcomes Inhibition of Fracture Healing in the Diabetic Rat: A Pilot Study

“…We injected 54 male Sprague-Dawley rats (200 g) with 50 mg/kg streptozotocin in 0.1 mol/L citrate buffer subcutaneously in the highly vascular region near the base of the tail to produce insulin-dependent diabetes mellitus (Table 1) [12,17]. Eighteen additional animals were injected with citrate buffer only to create nondiabetic controls.…”

MECHANISMS IN ENDOCRINOLOGY: Mechanisms and evaluation of bone fragility in type 1 diabetes mellitus

“…Poorly controlled T1DM is often attended by dyslipidaemia, which is associated with increased PPARg2 expression, impaired osteoblast differentiation and marrow adiposity (80). Finally, theories derived to account for the bone loss in T1DM must also acknowledge reports of abnormalities in circulating levels of the adipokines (leptin, adiponectin), amylin, prostaglandins and glucocorticoids in both experimental and human T1DM, which may negatively impact on bone health (16,111,112,113).…”