HIF-stabilization prevents delayed fracture healing

Abstract

<jats:title>Abstract</jats:title><jats:p>The initial phase of fracture healing decides on success of bone regeneration and is characterized by an inflammatory milieu and low oxygen tension (hypoxia). Negative interference with or prolongation of this fine-tuned initiation phase will ultimately lead to a delayed or incomplete healing such as non-unions which then requires an effective and gentle therapeutic intervention. Common reasons include a dysregulated immune response, immunosuppression or a failure in cellular adaptation to the inflammatory hypoxic milieu of the fracture gap and a reduction in vascularizing capacity by environmental noxious agents (e.g. rheumatoid arthritis, smoking). The hypoxia-inducible factor (HIF)-1α is responsible for the cellular adaptation to hypoxia, activating angiogenesis and supporting cell attraction and migration to the fracture gap. Here, we hypothesized that stabilizing HIF-1α could be a cost-effective and low-risk prevention strategy of fracture healing disorders. Therefore, we combined a well-known HIF-stabilizer – deferoxamine (DFO) – and a less known HIF-enhancer – macrophage migration inhibitory factor (MIF) – to synergistically induce improved fracture healing. Stabilization of HIF-1α enhanced calcification and osteogenic differentiation of MSCs <jats:italic>in vitro</jats:italic>. <jats:italic>In vivo</jats:italic>, the application of DFO with or without MIF during the initial healing phase accelerated callus mineralization and vessel formation in a clinically relevant mouse-osteotomy-model in a compromised healing setting. Our findings provide support for a promising preventive strategy towards bone healing disorders in patients with a higher risk due to e.g. delayed neovascularization by accelerating fracture healing using DFO and MIF to stabilize HIF-1α.</jats:p>

Functional Scaffold-Free Bone Equivalents Induce Osteogenic and Angiogenic Processes in a Human In Vitro Fracture Hematoma Model

“…In addition, pro-inflammatory processes were more pronounced, which is in accordance with current findings in a mouse-osteotomy model revealing the activation of, for example, C-X-C motif chemokine ligand 3 (Cxcl3) or metallothionein 3 (Mt3) expression at day 3 after application of DFO in the fracture gap. (20) We did not expect a strong upregulation of osteogenic markers or changes in the SFBCs, which normally require longer treatment periods. (29) Nevertheless, there are many ways to foster the current approach.…”

“…DFO is an iron chelator, which inhibits prolylhydroxylases to chemically stabilize HIF and is a well-known osteoinductive substance. (20) After co-cultivation for 48 hours and supplementation of DFO, we found that DFO triggered the expression of osteogenic, angiogenic, and hypoxia-related genes in the in vitro FH with barely any effect on the SFBCs (Fig. 5B).…”