Indiana University-Purdue University Indianapolis (IUPUI) / Current interventions used to reduce skeletal fragility are insufficient at enhancing bone across multiple hierarchical levels. Bisphosphonates, such as Zoledronate (ZOL), treat a variety of bone disorders by increasing bone mass and bone mineral density to decrease fracture risk. Despite the mass-based improvements, bisphosphonate use has been shown to compromise bone quality. Alternatively, Raloxifene (RAL) has recently been demonstrated to improve tissue quality and overall mechanical properties by binding to collagen and increasing tissue hydration in a cell-independent manner. We hypothesized that a combination of RAL and ZOL would improve mechanical and material properties of bone more than either monotherapy alone by enhancing both quantity and quality of bone. In this study, wildtype (WT) and heterozygous (OIM+/-) male mice from the Osteogenesis Imperfecta (OI) murine model were treated with either RAL, ZOL, or RAL and ZOL from 8 weeks to 16 weeks of age. Combination treatment resulted in higher trabecular architecture, cortical mechanical properties, and cortical fracture toughness in diseased mouse bone. Two fracture toughness properties, direct measures of the tissue’s ability to resist the initiation and propagation of a crack, were significantly improved with combination treatment in OIM+/- compared to control. There was no significant effect on fracture toughness with either monotherapy alone in either genotype. Following the mass-based effects of ZOL, bone volume fraction was significantly higher with combination treatment in both genotypes. Similar results were seen in trabecular number. Combination treatment resulted in higher ultimate stress in both genotypes, with RAL additionally increasing ultimate stress in OIM+/-. RAL and combination treatment in OIM+/- also produced a higher resilience compared to the control. Given no significant changes in cortical geometry, these mechanical alterations were likely driven by the quality-based effects of RAL. In conclusion, this study demonstrates the beneficial effects of using combination therapy to increase bone mass while simultaneously improving tissue quality, especially to enhance the mechanical integrity of diseased bone. Combination therapies could be a future mechanism to improve bone health and combat skeletal fragility on multiple hierarchical levels.

Current interventions used to reduce skeletal fragility are insufficient at enhancing bone across multiple hierarchical levels. Bisphosphonates, such as Zoledronate (ZOL), treat a variety of bone disorders by increasing bone mass and bone mineral density to decrease fracture risk. Despite the mass-based improvements, bisphosphonate use has been shown to compromise bone quality. Alternatively, Raloxifene (RAL) has recently been demonstrated to improve tissue quality and overall mechanical properties by binding to collagen and increasing tissue hydration in a cell-independent manner. We hypothesized that a combination of RAL and ZOL would improve mechanical and material properties of bone more than either monotherapy alone by enhancing both quantity and quality of bone. In this study, wildtype (WT) and heterozygous (OIM+/-) male mice from the Osteogenesis Imperfecta (OI) murine model were treated with either RAL, ZOL, or RAL and ZOL from 8 weeks to 16 weeks of age. Combination treatment resulted in higher trabecular architecture, cortical mechanical properties, and cortical fracture toughness in diseased mouse bone. Two fracture toughness properties, direct measures of the tissue’s ability to resist the initiation and propagation of a crack, were significantly improved with combination treatment in OIM+/- compared to control. There was no significant effect on fracture toughness with either monotherapy alone in either genotype. Following the mass-based effects of ZOL, bone volume fraction was significantly higher with combination treatment in both genotypes. Similar results were seen in trabecular number. Combination treatment resulted in higher ultimate stress in both genotypes, with RAL additionally increasing ultimate stress in OIM+/-. RAL and combination treatment in OIM+/- also produced a higher resilience compared to the control. Given no significant changes in cortical geometry, these mechanical alterations were likely driven by the quality-based effects of RAL. In conclusion, this study demonstrates the beneficial effects of using combination therapy to increase bone mass while simultaneously improving tissue quality, especially to enhance the mechanical integrity of diseased bone. Combination therapies could be a future mechanism to improve bone health and combat skeletal fragility on multiple hierarchical levels.