Changes in Serum Dickkopf-1, RANK Ligand, Osteoprotegerin, and Bone Mineral Density after Allogeneic Hematopoietic Stem Cell Transplantation Treatment

BACKGROUND: Dickkopf-1 (DKK1) regulates bone formation by inhibiting canonical Wnt/β-catenin pathway signaling, and indirectly enhances osteoclastic activity by altering the expression ratio of receptor activator of nuclear factor-κB ligand (RANKL) relative to osteoprotegerin (OPG). However, it is difficult to explain continued bone loss after allogeneic stem cell transplantation (allo-SCT) in terms of changes in only RANKL and OPG. Few studies have evaluated changes in DKK1 after allo-SCT. METHODS: We prospectively enrolled 36 patients with hematologic malignancies who were scheduled for allo-SCT treatment. Serum DKK1, OPG, and RANKL levels were measured before (baseline), and at 1, 4, 12, 24, and 48 weeks after allo-SCT treatment. Bone mineral density (BMD) was assessed using dual-energy X-ray absorptiometry before (baseline) and 24 and 48 weeks after allo-SCT treatment. RESULTS: After allo-SCT treatment, the DKK1 level decreased rapidly, returned to baseline during the first 4 weeks, and remained elevated for 48 weeks (P<0.0001 for changes observed over time). The serum RANKL/OPG ratio peaked at 4 weeks and then declined (P<0.001 for changes observed over time). BMD decreased relative to the baseline at all timepoints during the study period, and the lumbar spine in female patients had the largest decline (–11.3%±1.6% relative to the baseline at 48 weeks, P<0.05). CONCLUSION: Serum DKK1 levels rapidly decreased at 1 week and then continued to increase for 48 weeks; bone mass decreased for 48 weeks following engraftment in patients treated with allo-SCT, suggesting that DKK1-mediated inhibition of osteoblast differentiation plays a role in bone loss in patients undergoing allo-SCT.