Bone loss caused by iron overload in a murine model: importance of oxidative stress.

Osteoporosis is a frequent problem in disorders characterized by iron overload, such as the thalassemias and hereditary hemochromatosis. The exact role of iron in the development of osteoporosis in these disorders is not established. To define the effect of iron excess in bone, we generated an iron-overloaded mouse by injecting iron dextran at 2 doses into C57/BL6 mice for 2 months. Compared with the placebo group, iron-overloaded mice exhibited dose-dependent increased tissue iron content, changes in bone composition, and trabecular and cortical thinning of bone accompanied by increased bone resorption. Iron-overloaded mice had increased reactive oxygen species and elevated serum tumor necrosis factor-α and interleukin-6 concentrations that correlated with severity of iron overload. Treatment of iron-overloaded mice with the antioxidant N-acetyl-L-cysteine prevented the development of trabecular but not cortical bone abnormalities. This is the first study to demonstrate that iron overload in mice results in increased bone resorption and oxidative stress, leading to changes in bone microarchitecture and material properties and thus bone loss.

Changes in bone microarchitecture and biomechanical properties in the th3 thalassemia mouse are associated with decreased bone turnover and occur during the period of bone accrual.

Osteoporosis and fractures occur frequently in patients with beta-thalassemias, a group of congenital hemolytic anemias characterized by decreased synthesis of the beta chain of hemoglobin. In this study, we determined the bone abnormalities of the th3 thalassemia mouse, generated by deletion of the mouse beta-chain genes. The heterozygous th3/+ mouse has moderate anemia and serves as a model of beta-thalassemia intermedia, which represents the mild thalassemia phenotype. The th3/th3 mouse has lethal anemia and is a model of beta-thalassemia major, which is characterized by life-threatening anemia requiring regular transfusions to sustain life. Compared to controls, (1) microCT of trabecular bone showed decreased bone volume fraction, number of trabeculae, and trabecular thickness in both th3/+ and th3/th3 (P < 0.05); (2) cortical bone analysis showed thinner cortices and increased marrow area in th3/+ (P < 0.05); (3) microCT abnormalities in th3/+ mice were present by 2 months and did not worsen with age; (4) histomorphometry was significant for decreased bone formation and resorption in both th3/+ and th3/th3, and expression of cathepsin K and osteocalcin from bone of both th3/+ and th3/th3 animals was reduced (P < 0.05); (5) biomechanics showed reduced maximum load, maximum moment, and structural stiffness in both th3/+ and th3/th3 (P < 0.01). In conclusion, the th3 mouse model of thalassemia manifests bone changes reminiscent of those in humans and can be used for further bone studies in thalassemia. Bone changes are associated with decreased bone turnover and develop early during the period of bone accrual.