Hydroxyapatite: An Antibiotic Recruiting Moiety for Local Treatment and Prevention of Bone Infections.

Treatment of chronic osteomyelitis by radical debridement and filling of the dead space with antibiotic containing calcium sulphate/hydroxyapatite (CaS/HA) bone substitute has shown excellent long-term outcomes. However, in extensive infections, sessile bacteria may remain in bone cells or soft tissues protected by biofilm leading to recurrences. The primary aim of this study was to evaluate if systemically administrated tetracycline (TET) could bind to pre-implanted HA particles and impart an anti-bacterial effect locally. In-vitro studies indicated that the binding of TET to nano- and micro-sized HA particles was rapid and plateaued already at 1 h. Since protein passivation of HA after in-vivo implantation could affect HA-TET interaction, we investigated the effect of serum exposure on HA-TET binding in an antibacterial assay. Although, serum exposure reduced the zone of inhibition (ZOI) of Staphylococcus aureus, a significant ZOI could still be observed after pre-incubation of HA with serum. We could in addition show that zoledronic acid (ZA) competes for the same binding sites as TET and that exposure to high doses of ZA led to reduced TET-HA binding. In an in-vivo setting, we then confirmed that systemically administered TET seeks HA particles which were pre-implanted in a muscle and subcutaneous pouches in rats and mice respectively, preventing HA particles from being colonized by S. aureus. Clinical Significance: This study describes a new drug delivery method which could prevent bacterial colonization of a HA biomaterial and reduce recurrences in bone infection. This article is protected by copyright. All rights reserved.