Co-administration of Vancomycin and BMP-2 on Staphylococcus/Bone Cell Co-culture

Objectives: Repair and regeneration of a contaminated large bone defect remains a significant clinical challenge.  The standard of care is first to administer antibiotics to treat infection followed by the use of bone grafts and bone growth factors to aid bone repair and regeneration. Here we attempt to establish an in vitro bacteria/bone cell co-culture model system and begin preliminary dose-dependence studies of dual administration of antibiotic and growth factor in vitro aimed to mimic in vivo localized drug delivery.

Methods: Briefly, we examined the effect of single or dual administration of antibiotic, vancomycin (VAN) at 0-16μg/mL and bone morphogenetic protein 2 (BMP-2) at 0-100ng/mL to both methicillin sensitive S. aureus (the major offender in bone graft infection) and mouse bone marrow stromal cells (mBMSC) in both mono and co-culture conditions.  Cell metabolic activity, live/dead staining, dsDNA amount, and alkaline phosphatase activity were measured to assess cell viability, proliferation and differentiation.  An interleukin-6 ELISA kit was used to test the bone cell inflammation response in the presence of bacteria.

Results: Our results indicate that when delivered together in co-culture, VAN and BMP-2 maintain their primary functions as an antibiotic and growth factor respectively.  Most interestingly, this dual-delivery type of approach has shown itself to be effective at lower concentrations of VAN than an approach relying strictly on the antibiotic.

Conclusion: It may be that BMP-2 gives the mBMSCs a greater chance to proliferate and differentiate before becoming infected.  To our knowledge, this study is the first to demonstrate that a lower concentration of vancomycin in treatments with BMP-2 was necessary to achieve almost complete suppression of bacterial growth compared to treatments without BMP-2.