Bone grafting is currently the gold standard for filling in massive skeletal defects. However, once a bone graft is infected by methicillin-resistant S. aureus (MRSA) a common pathogen, infection is very difficult to treat due to the lack of vascularity and perfusion for antimicrobial bioavailability. Bone graft infection results in not ony microbial habitation, but also triggers innate immune inflammatory cytokine storms. Inflammation is meant to repel pathogens but excessive inflammation destroys bone just as the Ebola viral infection through a series of cytokine storms destroys its host. The U.S. Department of Health and Human Services (HHS) is pushing to minimize infection, one of the most important 'Quality and Safety' indicators. Therefore, there is a desperate need for developing a new strategy to prevent or reduce bone graft-associated infections. Our proposal formulates a therapeutic application of bisphosphonate-conjugated nano-micro-size-bubbles (BNB) that can load vancomycin and inflammatory kinase inhibitors for the treatment of MRSA bone graft infections. Technically, we optimized drug loading, release-kinetics, bone attachment, and the bactericidal effect of BNB. From a mechanism perspective, microarray, protein kinase array, and confirmatory RT-PCR showed MRSA- induction of inflammatory-osteoclastogenic cytokine storms that were primarily mediated by pERK1/2 in MRSA-infected osteoblasts. Osx-Cre;DN MEK1 mice with defective ERK1/2 phosphorylation in osteoblasts or AZD 6244 (a clinical grade MEK1-ERK1/2 phosphorylation inhibitor) treatments exhibited suppressed innate inflammatory response and osteoclastogenesis in response to bacterial toxins or MRSA in vivo and in vitro. We posit a central hypothesis that vancomycin+AZD6244-loaded BNB reduce post-operative bone infections and inflammatory graft resorption following MRSA infection.
Three Specific Aims are Aim 1 (Anti-Microbial Technology): To establish the efficacy of drug-loaded-BNB grafts to prevent infection and innate immune inflammatory reaction against MRSA infection in vitro;
Aim 2 (Mechanism): To determine a role of pERK1/2 in MRSA-induced cytokine storms by osteoblasts and subsequent inflammation-associated bone loss in vitro and in vivo;
and Aim 3 (Pre-Clinical Translation): To establish a new preventive & therapeutic regimen concurrently treating MRSA infection and inflammation with BNB in an animal model of infected bone grafting. We will conduct a series of mechanistic experiments using a clinical-grade pERK1/2 inhibitor and Osx-Cre;DN MEK1 mice with defective ERK1/2 phosphorylation regarding mRNA expression of RANKL, MCSF, TNF, IL-1b, IL-6 in MRSA-infected human and murine osteoblasts in vitro. We will conduct clinically relevant intercalary femoral bone grafting experiments in mice and determine whether vancomycin + AZD-BNB prevents or reduces infection and excessive inflammation following MRSA-infected bone grating by analyzing radiographs, microCT, histology, and biomechanical testing data. The proposed technique and therapeutic concepts may be extended to prevent or treat other types of bone or bio-implant infections and bacterial strains with high impact.
Bone grafts are invaluable for reconstruction of massive skeletal defects related to high-energy traumas, tumor resection and revision arthroplasties. However, they are prone to microbial infections (ex. Methicillin-resistant S. aureus) that can trigger bone destroying inflammatory cytokine storms; serious complications that can have dire consequences. The lack of blood flow within bone grafts limits the delivery of systemic antibiotics. We propose that bisphosphonate PLGA nano-micro-size-bubbles (BNB) can load and release vancomycin and inflammatory kinase inhibitors for the treatment of MRSA bone graft infections and associated inflammation.
