A Novel Injectable Hydrogel Incorporating Lipoxin for Treatment of Inflammation-mediated Bone Resorption

Abstract

Increased inflammation can disturb bone homeostasis leading to increased osteoclastogenesis and bone resorption. Studies have demonstrated that specialized pro-resolving lipid mediators such as lipoxins, can counteract inflammation and reduce bone loss. Despite the promising results, lipoxins may not be very stable and will require a more efficient delivery method that allows them to remain at the target site for a sufficient amount of time without disintegration. This study aims to develop a gelatin-based injectable hydrogel that will contain lipoxins for the treatment of inflammation-mediated bone resorption. Gelatin-hydroxyphenylpropionic acid (Gtn-HPA) cross-linked using horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) was used as a hydrogel delivery vehicle. Aspirin- triggered Lipoxin A4 (ATL A4) was incorporated in the hydrogel. The impact of Lipoxin incorporation on the cross-linking of the hydrogel was investigated using a tube tilting method. The release profile of Lipoxins from the hydrogel was studied by incubating the hydrogel in PBS and measuring lipoxin release at predetermined timepoints. Finally, a neonatal rat calvarial organ culture model was used to test the impact of Lipoxins released from hydrogel on inflammation- mediated bone resorption. Our results indicate that Lipoxins can be successfully incorporated in the Gtn-HPA hydrogel. However, at higher doses this may result in increased gelation time. The incorporated Lipoxins can be released from the gelatin matrix and the release rate can be controlled by varying the gel weight percentage and degree of cross-linking. Softer gels release more of the original lipoxin content compared to stiffer gels. Lastly, the reduction of inflammation-mediated bone resorption from a single dose of Lipoxins released from the hydrogel was comparable to multiple doses of Lipoxins added directly to the medium in a neonatal rat calvarial bone organ culture model. The promising data from this study provides the foundation for the development of a new therapeutic modality for the treatment of conditions characterized by inflammation-mediated bone loss.