This article was originally published here

J Bone Miner Res. 2022 May 26. doi: 10.1002/jbmr.4570. Online ahead of print.

Fracture healing is impaired in the setting of infection, which begets protracted inflammation. The most problematic causative agent of musculoskeletal infection is methicillin-resistant Staphylococcus aureus (MRSA). We hypothesized that modulation of excessive inflammation combined with cell-penetrating antibiotic treatments facilitates fracture healing in a murine MRSA-infected femoral fracture model. Sterile and MRSA-contaminated open transverse femoral osteotomies were induced in 10-week-old male C57BL/6 mice and fixed via intramedullary nailing. In the initial therapeutic cohort, empty, vancomycin- (V), rifampin- (R), vancomycin-rifampin- (VR), or vancomycin-rifampin-Trametinib (VRT) hydrogels were applied to the fracture site intraoperatively. Rifampin was included due its ability to penetrate eukaryotic cells to target intracellular bacteria. Unbiased screening demonstrated ERK activation as upregulated in the setting of MRSA infection. As such, the FDA-approved Mitogen-activated protein kinase kinase (MEK)1-pERK1/2 inhibitor Trametinib was evaluated as an adjunctive therapeutic agent to selectively mitigate excessive inflammation following infected fracture. Two additional cohorts were created mimicking immediate and delayed postoperative antibiotic administration. Systemic vancomycin or VR was administered for two weeks, followed by two weeks of VRT hydrogel or oral Trametinib therapy. Hematologic, histological, and cytokine analyses were performed using serum and tissue isolates obtained at distinct postoperative intervals. Radiography and micro-computed tomography (μCT) were employed to assess fracture healing. Pro-inflammatory cytokine levels remained elevated in MRSA-infected mice with antibiotic treatment alone, but increasingly normalized with Trametinib therapy. Impaired callus formation and malunion were consistently observed in the MRSA-infected groups and was partially salvaged with systemic antibiotic treatment alone. Mice that received VR alongside adjuvant MEK1-pERK1/2 inhibition displayed the greatest restoration of bone and osseous union. A combinatorial approach involving adjuvant cell-penetrating antibiotic treatments alongside mitigation of excessive inflammation enhanced healing of infected fractures. This article is protected by copyright. All rights reserved.