RANKL Inhibition Improves Bone Properties in a Mouse Model of Osteogenesis Imperfecta

Abstract

Recently, a new class of agents targeting the receptor activator of nuclear factor-κB ligand (RANKL) pathway has been developed for the treatment of osteoporosis and other bone diseases. In the current study, inhibition of the RANKL pathway was evaluated to assess effects on "bone quality" and fracture incidence in an animal model of osteogenesis imperfect (OI), the oim/oim mouse. Juvenile oim/oim (~6 weeks old) and wildtype (+/+) mice were treated with either a RANKL inhibitor (RANKFc) or saline. After treatment, bone density increased significantly in the femurs of both genotypes. Femoral length decreased with RANK-Fc in +/+ mice. Geometric measurements at mid-diaphysis in the oim/oim groups showed increases in the ML periosteal and endosteal diameters and AP cortical thickness in the treated groups. Within +/+ groups, ML cortical thickness and ML femoral periosteal diameter were significantly increased with RANK-Fc. Biomechanical testing revealed increased stiffness in oim/oim and +/+ mice. Total strain was increased with treatment in the +/+ mice. Histologically, RANKL inhibition resulted in retained growth plate cartilage in both genotypes. The average number of fractures sustained by RANK-Fc-treated oim/oim mice was not significantly decreased compared to saline treated oim/oim mice. This preclinical study demonstrated that RANKL inhibition at the current dose improved density and some geometric and biomechanical properties of oim/oim bone, but it did not decrease fracture incidence. Further studies that address commencement of therapy at earlier time points are needed to determine whether this mode of therapy will be clinically useful in OI.

Are Changes in Composition in Response to Treatment of a Mouse Model of Osteogenesis Imperfecta Sex-dependent?

“…Treatment ended 12 weeks after the transition time point. Doses of RANK-Fc and ALN were based on results of previous studies that showed increased bone mineral density without side effects using the same dose [1][2][3]. Weaning was carried out between 3 and 4 weeks.…”

“…Harvested femora, fixed in 100% ethanol and then embedded in PMMA, were cut into three to five longitudinal sections (1-2 lm) and the distal ends examined by FTIR imaging (Perkin Elmer model Spotlight 300 imaging system; Perkin Elmer, Waltham, MA, USA) as detailed elsewhere [1,19]. Briefly, areas of bone corresponding to cortical or cancellous regions (approximately 60,000 um 2 each) were imaged separately in three longitudinal sections, cut through the center of the shaft, with three to five different regions examined per section at 6.25-lm spatial resolution.…”

“…A power study with FTIR imaging of collagen maturity as the outcome selected, based on an earlier treatment study [1], indicated for a = 0.05, b = 80%, four mice per genotype per sex, were needed to address the question of whether oim/ oim mice showed sexual dimorphism in compositional properties at 6.5 months of age. This calculation assumed comparisons would be of treated versus untreated animals of the same genotype.…”

Comparable outcomes in fracture reduction and bone properties with RANKL inhibition and alendronate treatment in a mouse model of osteogenesis imperfecta

“…Heterozygous oim/ + mice have osteopenia but typically no spontaneous fractures and have been used as a model of mild OI [35]. Homozygous oim/oim mice have been used in a number of studies to evaluate the effect of bisphosphonates [36-38] and RANKL inhibition in OI [24,39]. The bisphosphonate alendronate (ALN) has been shown to increase BMD, alter geometric and biomechanical properties of oim/oim bone and reduce fractures in these mice [36-38] whereas RANKL inhibition was also found to increase BMD and alter geometric and biomechanical properties [24,40] but to have no discernible effect on fracture incidence [39].…”

“…Homozygous oim/oim mice have been used in a number of studies to evaluate the effect of bisphosphonates [36-38] and RANKL inhibition in OI [24,39]. The bisphosphonate alendronate (ALN) has been shown to increase BMD, alter geometric and biomechanical properties of oim/oim bone and reduce fractures in these mice [36-38] whereas RANKL inhibition was also found to increase BMD and alter geometric and biomechanical properties [24,40] but to have no discernible effect on fracture incidence [39]. It was hypothesized that the lack of fracture reduction with RANKL inhibition was due to a relatively late start (6 weeks of age) of treatment and a high baseline number of fractures in the previous study [39,40].…”