Comparison of Effects of the Bisphosphonate Alendronate Versus the RANKL Inhibitor Denosumab on Murine Fracture Healing

Abstract

The role of osteoclast-mediated resorption during fracture healing was assessed. The impact of two osteoclast inhibitors with different mechanisms of action, alendronate (ALN) and denosumab (DMAB), were examined during fracture healing. Male human RANKL knock-in mice that express a chimeric (human/ murine) form of RANKL received unilateral transverse femur fractures. Mice were treated biweekly with ALN 0.1 mg/kg, DMAB 10 mg/kg, or PBS (control) 0.1 ml until death at 21 and 42 days after fracture. Treatment efficacy assessed by serum levels of TRACP 5b showed almost a complete elimination of TRACP 5b levels in the DMAB-treated animals but only ;25% reduction of serum levels in the ALN-treated mice. Mechanical testing showed that fractured femurs from both ALN and DMAB groups had significantly increased mechanical properties at day 42 compared with controls. mCT analysis showed that callus tissues from DMAB-treated mice had significantly greater percent bone volume and BMD than did both control and ALN-treated tissues at both 21 and 42 days, whereas ALN-treated bones only had greater percent bone volume and BMC than control at 42 days. Qualitative histological analysis showed that the 21-and 42-day ALN and DMAB groups had greater amounts of unresorbed cartilage or mineralized cartilage matrix compared with the controls, whereas unresorbed cartilage could still be seen in the DMAB groups at 42 days after fracture. Although ALN and DMAB delayed the removal of cartilage and the remodeling of the fracture callus, this did not diminish the mechanical integrity of the healing fractures in mice receiving these treatments. In contrast, strength and stiffness were enhanced in these treatment groups compared with control bones.

Unraveling macrophage contributions to bone repair

“…12 Nuclear factor-kappa B ligand inhibition in animal fracture models has established the importance of osteoclasts/chondroclasts in cartilaginous-to-boney callus transition. [55][56][57] Profound inhibition of osteoclast formation was confirmed in most models. Interestingly, the remaining callus consisted of mineralized and vascularized cartilage 55 that was mechanically sound.…”

“…Interestingly, the remaining callus consisted of mineralized and vascularized cartilage 55 that was mechanically sound. 57 MMPs, 55 particularly MMP-9 54 and MMP-13, 58 have been implicated as important molecular mediators of soft-tohard callus transition. In vitro data support the fact that macrophages can efficiently produce MMPs and degrade the cartilage matrix, 59,60 with MMP production being a forte of M1 macrophages.…”

Prevention of glucocorticoid‐induced bone loss in mice by inhibition of RANKL

“…Human RANKL-knockin mice carry the human instead of the murine exon 5 in their RANKL gene, and as a result express a chimeric RANKL protein that is capable of inducing bone resorption in mice while being fully inhibited by denosumab (21). Human RANKL-knockin mice represent the only small animal model for studying the safety and pharmacologic application of denosumab, which to date have included fracture repair (22) and ovariectomy-induced bone loss (23).…”

Bone Regeneration Is Promoted by Orally Administered Bovine Lactoferrin in a Rabbit Tibial Distraction Osteogenesis Model

“…The region of interest was defined as the distracted area located between the two ends of the fractured bone. In the region of interest, the medullary canal volume was excluded from evaluation; after segmentation, the following parameters were calculated in the new-formed bone tissues according to a previous study [8]: bone volume fraction, trabecular number, trabecular thickness, and trabecular separation. The bone volume fraction represented the portion of mineralized tissue, while trabecular number, thickness, and separation provided detailed information regarding the amount, thickness, and organization of trabeculae.…”