RA Denosumab on Bone Microstructure Study

Rheumatoid arthritis (RA) is a chronic, systemic inflammatory disease most typical in women. Generalized osteoporosis is common in RA, at axial and appendicular skeleton and in females and males. Denosumab is a fully humanized IgG monoclonal antibody that targets the receptor activator of nuclear factor κB ligand (RANKL). Denosumab prevents the binding and activation of the RANK receptors on the osteoclasts and hence inhibits osteoclasts formation, activation, function and survival. Denosumab results in more rapid and greater reductions in bone remodeling and correspondingly greater increases in areal bone mineral density (aBMD) at all skeletal sites. Denosumab was approved by FDA in June 2010 for the treatment of postmenopausal women with osteoporosis at high risk of fracture. Denosumab (Prolia®) is also licensed in Hong Kong.

A high-resolution peripheral quantitative computed tomography (HR-pQCT) capable of achieving an isotropic voxel size of 80μm at tolerable radiation doses (3μSv) is available for the assessment of trabecular and cortical microarchitecture at the distal radius and tibia. This technique bears excellent precision for both density and microstructure measures. Denosumab's greater potency in suppressing bone remodeling and greater effect on areal BMD than alendronate, particularly at predominantly cortical sites such as the distal third of the radius, may reflect the differing mechanism of action of these drugs, which, in turn, influence bone microarchitecture.

The aim of this study is to compare the effects of denosumab and a current standard treatment on cortical and trabecular microarchitecture at the radius and second metacarpal in RA patients with low bone mineral density using HR-pQCT during a 6-month open-label randomized controlled study. One bisphosphonate, namely alendronate sodium (or alendronate) is chosen to generate a heterogeneous and comparable active control group. This is a 6-month open-label randomized controlled clinical trial. Forty ambulatory Chinese females, who consent to receive alendronate as standard treatment subjective to the randomization, will be enrolled from the rheumatology clinic of the Prince of Wales Hospital in this study. Subjects will be randomized to 2 groups receiving: 1) subcutaneous injection of denosumab 60mg (Prolia®) every 6 months (n=20), or 2) a standard treatment: oral alendronate weekly (Fosamax® once weekly 70 mg, n=20). In addition, all patients will be given a daily calcium supplement (1500mg caltrate /day) and 1 multivitamin tablet per day. Efficacy and safety assessment will be performed at baseline, month 3 and month 6. aBMD of lumbar spine, total hip and non-dominant distal radius will be measured using dual-energy X-ray absorptiometry (DXA) and microarchitecture of bone is measured at the non-dominant distal radius and the second metacarpal bone of the non-dominant hand using HR-pQCT.