Influence of Fatigue Loading and Bone Turnover on Bone Strength and Pattern of Experimental Fractures of the Tibia in Mice

Mechanisms underlying the long-term and withdrawal effects of denosumab therapy on bone

Denosumab, a human monoclonal antibody against receptor activator of nuclear factor-κB ligand (RANKL), is a potent inhibitor of osteoclast differentiation and activity. As the first biologic drug used to treat osteoporosis, denosumab has shown potent anti-resorptive properties and anti-fracture efficacy. The effects of this drug are also unique compared with the effects of bisphosphonates: namely, long-term treatment with this drug results in a continuous gain of bone mineral density, whereas withdrawal of the drug results in a transient overshoot in bone turnover and rapid bone loss. Although the mechanisms for these specific effects remain incompletely understood, emerging experimental and clinical data have started to highlight potential biological and pharmacological mechanisms by which denosumab might affect osteoclasts, as well as osteoblasts, and cause both sustained bone gain and bone loss upon treatment cessation. This Perspective discusses those potential mechanisms and the future studies and clinical implications that might ensue from these findings.

Denosumab Discontinuation

PURPOSE OF REVIEW

To review the pathophysiology, the clinical consequences as well as way of mitigating the effects of denosumab discontinuation.

RECENT FINDINGS

Treatment with denosumab (DMAB) is reversible and upon discontinuation there is a rapid increase in bone turnover and a subsequent bone loss. During this phase of high bone turnover, an increased risk of fractures has been reported. Therefore, treatment with DMAB could be considered life-long. However, side-effects may prompt the need for discontinuation and moreover, treatment with DMAB may have increased BMD to levels where continuing treatment does not provide further fracture risk reduction. Patients stopping DMAB should be offered subsequent antiresorptive treatment with an intense monitoring regimen during the initial year as most of the bone loss occurs within these initial 12 months. In this review, we evaluated the literature published over the past 1 to 3 years investigating DMAB withdrawal with focus on bone turnover markers, bone mineral density, and fracture risk and the transition to other anti-osteoporosis therapies. Furthermore, we summarized the current recommendations of international guidelines. In this review, we evaluated the literature published over the past 1 to 3 years investigating denosumab (DMAB) discontinuation and the transition to other anti-osteoporosis therapies. Additionally, we summarized the current recommendations of international guidelines.

Effects of Long-Term Denosumab on Bone Histomorphometry and Mineralization in Women With Postmenopausal Osteoporosis

CONTEXT

Denosumab is a potent antiresorptive agent that reduces fractures in postmenopausal women with osteoporosis.

OBJECTIVE

Determine effects of up to 10 years of denosumab on bone histology, remodeling, and matrix mineralization characteristics.

DESIGN AND SETTING

International, multicenter, randomized, double-blind trial [Fracture Reduction Evaluation of Denosumab in Osteoporosis Every 6 Months (FREEDOM)] with a long-term open-label extension.

PATIENTS

Postmenopausal women with osteoporosis (92 women in FREEDOM, 46 in extension) who provided iliac bone biopsies, including 11 who provided biopsies at multiple time points.

INTERVENTIONS

FREEDOM subjects were randomized 1:1 to subcutaneous denosumab 60 mg or placebo every 6 months for 3 years. Long-term extension subjects continued receiving denosumab, open-label, for 7 additional years.

OUTCOMES

Bone histology, histomorphometry, matrix mineralization.

RESULTS

Ten-year denosumab biopsies showed normal histology. Bone histomorphometry indicated normal bone structure and reduced bone remodeling after 10 years of denosumab, similar to levels after 2 and/or 3 and 5 years of denosumab. The degree of mineralization of bone was increased and mineralization heterogeneity was reduced in the denosumab years 2/3 group vs placebo. Changes in these mineralization variables progressed from years 2/3 to year 5 of denosumab, but not thereafter.

CONCLUSIONS

Denosumab for 2/3, 5, and 10 years was associated with normal histology, low bone remodeling rate, increased matrix mineralization, and lower mineralization heterogeneity compared with placebo. These variables were unchanged from year 5 to year 10. These data, in combination with the maintenance of low fracture rates for up to 10 years as previously reported with denosumab therapy, suggest that strong, prolonged remodeling inhibition does not impair bone strength.