Raloxifene reduces skeletal fractures in an animal model of osteogenesis imperfecta

Abstract

Osteogenesis imperfecta (OI) is a genetic disease of Type I collagen and collagen-associated pathways that results in brittle bone behavior characterized by fracture and reduced mechanical properties. Based on previous work in our laboratory showing that raloxifene (RAL) can significantly improve bone mechanical properties through non-cellular mechanisms, we hypothesized that raloxifene would improve the mechanical properties of OI bone. In experiment 1, tibiae from female wild type (WT) and homozygous oim mice were subjected to in vitro soaking in RAL followed by mechanical tests. RAL soaking resulted in significantly higher post-yield displacement (+75% in WT, +472% in oim; p<0.004), with no effect on ultimate load or stiffness, in both WT and oim animals. In experiment 2, eight-week old WT and oim male mice were treated for eight weeks with saline vehicle (VEH) or RAL. Endpoint measures included assessment of in vivo skeletal fractures, bone density/geometry and mechanical properties. In vivo skeletal fractures of the femora, assessed by micro CT imaging, were significantly lower in oim-RAL (20%) compared to oim-VEH (48%, p=0.047). RAL led to significantly higher DXA-based BMD (p<0.01) and CT-based trabecular BV/TV in both WT and oim animals compared to those treated with VEH. Fracture toughness of the femora was lower in oim mice compared to WT and improved with RAL in both genotypes. These results suggest that raloxifene reduces the incidence of fracture in this mouse model of oim. Furthermore, they suggest that raloxifene's effects may be the result of both cellular (increased bone mass) and non-cellular (presumably changes in hydration) mechanisms, raising the possibility of using raloxifene, or related compounds, as a new approach for treating bone fragility associated with OI.

Raloxifene Improves Bone Mechanical Properties in Mice Previously Treated with Zoledronate

“…Recently, our lab has shown that raloxifene significantly increases bone hydration and this is associated with improved mechanical properties, most notably post-yield parameters [19]. These effects have been noted both in vivo and in vitro, in mice, rats, dogs and humans [19,20,24,33–35]. Since at least some of the effects from raloxifene are not cell-mediated, we hypothesized that treatment with raloxifene could significantly benefit the mechanical properties of bone in conditions such as bisphosphonate-treatment where the tissue becomes brittle.…”

“…The dose and duration of ZOL was chosen as it has shown efficacy in suppressing remodeling and affecting mechanical properties in this genetic strain [21]. The lower dose of RAL has been used previously and shown efficacy in vivo [24]; a higher dose was arbitrarily chosen as 4× higher to determine if dose-responses could be quantified. At 24 weeks of age, animals were euthanized and the right femurs were removed, wrapped in saline-soaked gauze, and frozen (−20C) for later analysis.…”

“…Specimens were loaded to failure at a rate of 2 mm/min, producing a force-displacement curve for each sample. Using a custom MATLAB program [24], structural and apparent material properties were determined. Apparent material properties were derived using standard beam-bending equations for four-point bending and geometric data from microCT analyses.…”

Skeletal Dysplasias: Growing Therapy for Growing Bones

“…Studies have demonstrated an increase in bone healing by callus formation when teriparatide is combined with BMP-7, a recombinant protein in bones (Morgan et al, 2008). Raloxifene has been shown to decrease the rate of bone fractures in mice (Berman et al, 2016) and may prove to be useful to decrease fractures in future human trials of OI. Denosumab is an antibody currently used to prevent fractures in post-menopausal women with osteoporosis (Cummings et al, 2009; Shaker et al, 2015) and is being evaluated to treat OI.…”

Effects of daily restraint with and without injections on skeletal properties in C57BL/6NHsd mice

“…Bones were tested to failure in 4 point bending (upper loading span of 3 mm, lower support span of 9 mm) in displacement control at a rate of 0.025 mm/s while hydrated with PBS. Using a custom MATLAB program 7 , structural and apparent material properties were determined. Apparent material properties were derived using standard beam-bending equations for four-point bending and geometric data from microCT.…”