Denosumab for the treatment of primary pediatric osteoporosis

Mitigating the Denosumab-Induced Rebound Phenomenon with Alternating Short- and Long-Acting Anti-resorptive Therapy in a Young Boy with Severe OI Type VI

Osteogenesis imperfecta (OI) type VI, a recessively inherited form of OI caused by mutations in SERPINF1, is a severe form distinguished by osteomalacia on bone histomorphometry. We describe a boy with severe OI type VI who was initially treated with intravenous (IV) zoledronic acid (ZA) at 1.4 years of age; however, a year later he transitioned to denosumab 1 mg/kg sub-cutaneously every three months in an effort to decrease fracture rates. After two years on denosumab, he presented with symptomatic hypercalcemia due to the denosumab-induced, hyper-resorptive rebound phenomenon. Laboratory parameters at the time of the rebound were as follows: elevated serum ionized calcium (1.62 mmol/L, N 1.16-1.36), elevated serum creatinine due to hypercalcemia-induced muscle catabolism (83 µmol/L, N 9-55), and suppressed parathyroid hormone (PTH) (< 0.7 pmol/L, N 1.3-5.8). The hypercalcemia was responsive to low-dose IV pamidronate, with a rapid decline in serum ionized calcium, and otherwise normalization of the aforementioned parameters within 10 days. To benefit from the powerful, albeit short-term, anti-resorptive effect of denosumab without further rebound episodes, he was treated thereafter with denosumab 1 mg/kg alternating every three months with IV ZA 0.025 mg/kg. Five years later, he remained on dual alternating anti-resorptive therapy without further rebound episodes, and an overall improvement in his clinical status. This novel pharmacological approach of alternating short- and long-term anti-resorptive therapy every three months has not previously been described. Our report suggests this strategy may be an effective method for prevention of the rebound phenomenon in select children for whom denosumab may be beneficial.

Novel Treatment Options in Childhood Bone Diseases

BACKGROUND

Several novel treatment options have recently become available in childhood bone diseases. The purpose of this article is to provide an update on some of the therapeutic agents used in the treatment of pediatric osteoporosis, X-linked hypophosphatemic rickets, and achondroplasia (ACH).

SUMMARY

Vitamin D3 and Ca supplementation remains the basis of childhood osteoporosis treatment. Bisphosphonate (BP) therapy is the main antiresorptive therapeutic option, while denosumab, a human monoclonal IgG2 antibody with high affinity and specificity for a primary regulator of bone resorption - RANKL, represents a possible alternative. Its potent inhibition of bone resorption and turnover process leads to continuous increase of bone mineral density throughout the treatment also in the pediatric population. With a half-life much shorter than BPs, its effects are rapidly reversible upon discontinuation. Safety and dosing concerns in children remain. Novel treatment options have recently become available in two rare bone diseases. Burosumab, a monoclonal antibody against FGF-23, has been approved for the treatment of children with X-linked hypophosphatemic rickets older than 1 year. It presents an effective, more etiology-based treatment for rickets compared to conventional therapy, without the need for multiple daily oral phosphate supplementation. Its long-term efficacy and safety are currently being investigated. After years of anticipation, a novel treatment option for ACH has become available. C-type natriuretic peptide analog vosoritide effectively increases proportional growth and has a reasonable safety profile in children >2 years. Its effect on other features of the disease and the final height is yet to be determined. Several other treatment options for ACH exploring different therapeutic approaches are currently being investigated.

KEY MESSAGES

Denosumab is effective in the treatment of childhood-onset osteoporosis; however, further studies are necessary to determine the optimal treatment protocol. Burosumab is more etiology-based and convenient in comparison to conventional treatment of X-linked hypophospha--temic rickets in children and adults. Vosoritide importantly changes the natural course of achondroplasia, at least in the short term.

Salidroside promoted osteogenic differentiation of adipose-derived stromal cells through Wnt/β-catenin signaling pathway

BACKGROUND

Bone disease causes short-term or long-term physical pain and disability. It is necessary to explore new drug for bone-related disease. This study aimed to explore the role and mechanism of Salidroside in promoting osteogenic differentiation of adipose-derived stromal cells (ADSCs).

METHODS

ADSCs were isolated and treated with different dose of Salidroside. Cell count kit-8 (CCK-8) assay was performed to assess the cell viability of ADSCs. Then, ALP and ARS staining were conducted to assess the early and late osteogenic capacity of ADSCs, respectively. Then, differentially expressed genes were obtained by R software. Then, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the differentially expressed genes were further analyzed. The expression of OCN, COL1A1, RUNX2, WNT3A, and β-catenin were measured by real-time PCR and Western blot analysis. Last, β-catenin was silenced by small interfering RNA.

RESULTS

Salidroside significantly increased the ADSCs viability at a dose-response manner. Moreover, Salidroside enhanced osteogenic capacity of ADSCs, which are identified by enhanced ALP activity and calcium deposition. A total of 543 differentially expressed genes were identified between normal and Salidroside-treated ADSCs. Among these differentially expressed genes, 345 genes were upregulated and 198 genes were downregulated. Differentially expressed genes enriched in the Wnt/β-catenin signaling pathway. Western blot assay indicated that Salidroside enhanced the WNT3A and β-catenin expression. Silencing β-catenin partially reversed the promotion effects of Salidroside. PCR and Western blot results further confirmed these results.

CONCLUSION

Salidroside promoted osteogenic differentiation of ADSCs through Wnt/β-catenin signaling pathway.