Additive effects of exogenous IL-12 supplementation and antibiotic treatment in infection prophylaxis.

The increasing clinical incidence and host risk of open fracture-associated infections, as well as the reduced effectiveness of conventional antibiotics to treat such infections, have driven the development of new therapies for the prophylaxis of open fracture-associated infections. We investigated percutaneous supplementation of a natural cytokine (i.e., interleukin 12p70 or IL-12) at an open fracture site to reduce open fracture-associated infections. We also determined the efficacy of the combination therapy of IL-12 and conventional antibiotic therapy in the prophylaxis of open fracture-associated infections. An open femur fracture infection model was produced by direct inoculation of a clinical isolate of Staphylococcus aureus after creating a femur fracture using rats. The animals were assigned to one of four groups: no drug administration, percutaneous supplementation of IL-12, intraperitoneal administration of the antibiotic ampicillin, or percutaneous IL-12 in combination with intraperitoneal ampicillin. Animals were euthanized at postoperative days 6, 10, 14, and 21. Percutaneous IL-12 led to a reduction in infection at postoperative days 6 and 10. For the first time, exogenous IL-12 was found to have additive effects in the prevention of infection when combined with conventional treatment (i.e., antibiotic therapy). Combination therapy of ampicillin and IL-12 substantially reduced the infection rate at postoperative day 6 and also decreased the time needed for complete inhibition of infection. Therefore, exogenous IL-12, providing a mechanism of protection independent of antibiotic resistance, complements the routine use of antibiotics.

Evaluation of local MCP-1 and IL-12 nanocoatings for infection prevention in open fractures.

The increasing incidence of bacterial infection and the appearance of Staphylococcus aureus (S. aureus) strains that are resistant to commonly used antibiotics has made it important to develop non-antibiotic approaches for infection prevention. The aim of this study was to develop local monocyte chemoattractant protein-1 (MCP-1) and interleukin-12 p70 (IL-12 p70) therapies to prevent S. aureus infection by enhancing the recruitment and activation of macrophages, which are believed to play an important role in infection prevention as the first line of defense against invading pathogens. Nanocoating systems for MCP-1 and IL-12 p70 deliveries were prepared, and their release characteristics desirable for infection prevention in open fractures were explored. Local MCP-1 therapy reduced S. aureus infection and influenced white blood cell populations, and local IL-12 p70 treatment had a more profound effect on preventing S. aureus infection. No synergistic relationship in decreasing S. aureus infection was observed when MCP-1 and IL-12 p70 treatments were combined. This reported new approach may reduce antibiotic use and antibiotic resistance.

An animal model for open femur fracture and osteomyelitis: Part I.

Infection is an everyday problem in orthopaedics and is quite common in open fracture management. To study this process and provide a basis to prevent infection, we developed a model that includes trauma (blunt fracture in the fashion of Bonnarens and Einhorn), surgical stabilization (standardized intramedullary K-wire fixation), and infection (Staphylococcus aureus inoculum). In this two-part study, we found that 10(2) colony-forming units of inoculum produced an optimal infection rate of 90-100%, which substantially challenged the immune system without overwhelming sepsis. We hypothesized that, in traumatic fractures, there is a specific immunological response that may lead to an increased rate of infection. In Part 2, we demonstrated immunosuppression (decreased Interleukin-12 levels) at days 6, 10, and 12 after fracture fixation versus nonfractured control groups (p < 0.05). This study describes a rat model of femur factures with osteomyelitis that allows investigation of posttraumatic immunosuppression.

An animal model for open femur fracture and osteomyelitis--Part II: Immunomodulation with systemic IL-12.

Infection resulting from open fracture is a common problem in orthopedics. The purpose of this project was to study the effect of Interleukin-12 (IL-12) systemic therapy on a previously established open fracture model. One hundred seven male Sprague-Dawley rats were assigned to five groups: (1) normal (baseline), (2) control (controlled for anesthesia), (3) fracture, (4) staph, and (5) staph and IL-12 (SIL). Each group was divided into four time periods: 6, 10, 14, and 21 days after injury and fixation. The operative groups had a standardized femur fracture and fixation using a Kirschner wire as an intramedullary device. The two infection groups (staph and SIL) were inoculated with Staphylococcus aureus following fracture and fixed with an identical technique. The SIL group was treated with systemic IL-12 for a total of 10 doses over 10 days. Significantly decreased serum IL-12 levels were noted at day 10 in the operative groups compared to the normal and control groups. The SIL group showed significantly higher macrophage activation levels and total platelet counts at day 21 compared to all the other groups. The overall infection rate was not changed by IL-12 supplementation; however, bacterial qualitative growth scores were significantly lower in the SIL group at day 10, which corresponded to the lowest level of systemic IL-12 in the fracture group.