Background Glucocorticoids (GC) represent most frequently-used anti-inflammatory drugs in rheumatology. However, especially if given at higher dosages for a longer time, they have the potential to induce adverse effects such as GC-induced delayed bone regeneration and osteoporosis. Several studies have demonstrated the negative influence of anti-inflammatory drugs during bone healing. One suggested mechanism is that GC inhibit the differentiation potential of invading mesenchymal stromal cells (MSC). Fracture healing is divided into four phases including the initial inflammatory phase where blood vessels are disrupted at the fracture site and inflammatory cells enter the area. It is thought that hypoxia influences the microenvironment. One key regulator of cellular adaption to hypoxia is the hypoxia-inducible factor- (HIF) that can be stabilized via different factors called chemical hypoxia inducers. HIF is a transcription factor and initiates processes that further the consecutive steps of healing and MSC differentiation.
Objectives Our study focuses on the understanding of GC induced effects on MSC differentiation and we aim at applying chemically hypoxia inducers to prevent negative side effects.
Methods Human bone marrow derived MSC were cultured and differentiated into osteoblasts under normoxic (37°C, 5% CO2, 18% O2) or hypoxic (37°C, 5% CO2, 1% O2) conditions. Different concentrations of Dexamethasone (10–3–10–8M) and chemical hypoxia inducers were examined. The calcification process during osteogenesis was analyzed using a quantifiable Alizarin Red staining method. Furthermore, we performed a preliminary proof of concept study in a mouse osteotomy model (3 weeks; n=2 per group).
Results We could demonstrate a concentration-dependent inhibitory effect of Dexamethasone on osteogenesis which could be considerably antagonized by hypoxia or chemically hypoxia inducers in vitro. In the mouse model, preliminary in vitro μCT data indicated a positive effect on healing processes by means of increased callus volume (TV, BV) after three weeks by applying chemical hypoxia inducers into the fracture gap at the time of the osteotomy compared to the controls.
Conclusions Our data demonstrate that hypoxia promotes osteogenic differentiation and has the ability to counteract the negative impact of GC on osseous differentiation. The preliminary in vivo data support the in vitro findings. Therefore, a combination of chemical hypoxia inducers may represent a promising tool to overcome bone healing disorders in GC treated patients.
Disclosure of Interest None declared
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