Liver-derived IGF-I regulates cortical bone mass but is dispensable for the osteogenic response to mechanical loading in female mice

Low circulating IGF-I is associated with increased fracture risk. Conditional depletion of IGF-I produced in osteoblasts or osteocytes inhibits the bone anabolic effect of mechanical loading. Here, we determined the role of endocrine IGF-I for the osteogenic response to mechanical loading in young adult and old female mice with adult, liver-specific IGF-I inactivation (LI-IGF-I−/− mice, serum IGF-I reduced by ≈70%) and control mice. The right tibia was subjected to short periods of axial cyclic compressive loading three times/wk for 2 wk, and measurements were performed using microcomputed tomography and mechanical testing by three-point bending. In the nonloaded left tibia, the LI-IGF-I−/− mice had lower cortical bone area and increased cortical porosity, resulting in reduced bone mechanical strength compared with the controls. Mechanical loading induced a similar response in LI-IGF-I−/− and control mice in terms of cortical bone area and trabecular bone volume fraction. In fact, mechanical loading produced a more marked increase in cortical bone mechanical strength, which was associated with a less marked increase in cortical porosity, in the LI-IGF-I−/− mice compared with the control mice. In conclusion, liver-derived IGF-I regulates cortical bone mass, cortical porosity, and mechanical strength under normal (nonloaded) conditions. However, despite an ∼70% reduction in circulating IGF-I, the osteogenic response to mechanical loading was not attenuated in the LI-IGF-I−/− mice.

Therapeutic Effect of Lipophilic and/or Hydrophilic Zinc Related Compound Injections on Alveolar Bone Mass in Zinc-Deficient Osteoporosis Rats

The purpose of this research is improvement of therapeutic treatment for periodontitis by using lipophilic and/or hydrophilic zinc materials. The sample suspension injections were prepared from zinc octanate, zinc stearate, zinc sulfate hepta-hydrate and tricalcium phosphate containing 6.17w/w% zinc. After administrating of all injections to around alveolar bone of zinc-deficient osteoporosis rats, plasma Zn concentration, bone mineral content and bone mechanical strength of jawbone and femur of Zn deficient rats were measured as therapeutic scores.