Analysis of circulating osteoclast and osteogenic precursors in patients with Gorham-Stout disease.

PURPOSE: Gorham-Stout disease is a very rare disorder characterized by progressive bone erosion and angiomatous proliferation; its etiopathogenesis is still unknown, and diagnosis is still performed by exclusion criteria. The alteration of bone remodeling activity has been reported in patients; in this study, we characterized circulating osteoclast and osteogenic precursors that could be important to better understand the osteolysis observed in patients. METHODS: Flow cytometry analysis of PBMC (Peripheral Blood Mononuclear Cells) was performed to characterize circulating osteoclast and osteogenic precursors in GSD patients (n = 9) compared to healthy donors (n = 55). Moreover, ELISA assays were assessed to evaluate serum levels of bone markers including RANK-L (Receptor activator of NF-κB ligand), OPG (Osteoprotegerin), BALP (Bone Alkaline Phosphatase) and OCN (Osteocalcin). RESULTS: We found an increase of CD16-/CD14+CD11b+ and CD115+/CD14+CD11b+ osteoclast precursors in GSD patients, with high levels of serum RANK-L that could reflect the increase of bone resorption activity observed in patients. Moreover, no significant alterations were found regarding osteogenic precursors and serum levels of BALP and OCN. CONCLUSION: The analysis of circulating bone cell precursors, as well as of RANK-L, could be relevant as an additional diagnostic tool for these patients and could be exploited for therapeutic purposes.

Mechanisms of acute hypercalcemia in pediatric patients following the interruption of Denosumab.

PURPOSE: Denosumab is a fully human monoclonal anti-RANK-L antibody that is clinically used to counteract the bone loss induced by exacerbated osteoclast activity. Indeed, its binding to RANK-L prevents the interaction RANK-L/receptor RANK that is essential for osteoclastogenesis and bone resorbing activity. Although there are many medications available to treat bone loss diseases, including bisphosphonates, Denosumab is highly effective since it reduces the bone erosion. The use in pediatric patients is safe. However, some concerns are related to the interruption of the treatment. Indeed, in this study, we reported hypercalcemia in two pediatric patients and alterations of circulating osteoclast precursors. METHODS: Peripheral Blood Mononuclear Cells (PBMC) were isolated from two pediatric patients with hypercalcemia after Denosumab interruption and from 10 controls. Cytofluorimetric analysis and in vitro osteoclastogenesis experiments were performed. RESULTS: Increase of CD16-CD14+CD11b+ cells was revealed in PBMC from patients reflecting the enhanced in vitro osteoclastogenesis. CONCLUSION: Our data suggest that precautions must be taken when Denosumab therapy is interrupted and gradual decrease of dose and/or timing of treatment should be performed. To prevent the onset of hypercalcemia that could be in the discontinuation phase, cytofluorimetric analysis of PBMC should be performed to evaluate osteoclast precursors.