Effects of TLR9 stimulation by CpG-ODN in implant-associated bone infections caused by Staphylococcus aureus
Final Report Abstract
TLR-9 ligand CpG oligodeoxynucleotide type B (CpG ODN) induces a proinflammatory environment. We evaluated the effects of a preoperative CpG ODN application in an implant-associated Staphylococcus aureus bone infection model by monitoring bacterial loads and cytokine and chemokine levels. A total of 95 rats were used in four different groups: CpG ODN group (group 1; n = 25), non-CpG- ODN group (group 2; n=25); saline pretreatment (group 3; n=25), and one uninfected group (group 4; n=20). A single dose of CpG-ODN was administered to the left tibialis anterior muscle 3 days prior to surgery and the tibia midshaft was osteotomized, stabilized by an intramedullary implant and subsequently contaminated with 103 colony forming units (CFUs) of S. aureus strain (DSMNo. 28763) in groups 1–3. The osteotomy gap in animals of group 4 was not contaminated with S. aureus and those animals did not receive any pretreatment. CpG ODN administration resulted in significant reduction of the bacterial load in tibia tissue homogenate and on the implant surface on day 1 post-infection compared to non-CpG-ODN pretreatment (p < 0.05; p < 0.05). Reductions in bacterial CFUs, compared to non-treated (saline) controls, were approximately 67% and 77% for bone tissue homogenates and implants. No bacteria were detected in uninfected rats. Early reduction of bacterial CFUs in the tibia was accompanied by increased levels of proinflammatory mediators MIP-2, IL-1β and RANTES in bone tissue milieu of the CpG ODN treated group compared to controls. At day 42 post-infection, bone marrow tissue of rats pretreated with CpG-ODN had comparable high bacterial CFU numbers as the non-CpG ODN or saline treated groups. Microbiological analysis of implants removed from CpG ODN treated rats showed high bacterial growth densities on their surfaces which were not different from those observed in controls. In histology, all animals of groups 1–3 showed established infected non-unions. Additionally, inflammatory mediator profiles in bone marrow homogenates of CpG ODN treated rats resembled those seen in infected controls. In this rat model, prophylactic administration of a single dose of CpG ODN, resulted in marked reduction of S. aureus load in the infected tibia during the initial stage of infection but failed to prevent development of chronic infection over time. In a second model, in which only an implantation of a 0.7 mm cannula without osteotomy was performed and in which the intramedullary canal was contaminated with 105 colony forming units (CFUs) of methicillin-resistant S. aureus (MRSA) strain (EDCC5246), there were no significant differences in the bacterial load on day 1and day 3 between the treatment groups. This result is in contrast to the findings from the first model in which an additional osteotomy was carried out. There are two possible explanations for this. First, the used amount of bacteria was too high in order to show any potential differences between the groups or, second, that the osteotomy has an influence on the effects of the CpG ODN application. The results from these studies, particularly from model A, encouraged us to investigate deeper the effects of CpG ODNs in osteoblasts. We recently finalized the first studies in which we could show that pretreatment of SAOS-2 cells with ODN2216 or ODN2006 managed to induce reactive oxygen species (ROS) production inside osteoblasts as measured by flow cytometry analysis. Moreover, treating SAOS-2 cells with the antioxidant Diphenyleneiodonium (DPI) obviously reduced S. aureus killing ability of TLR9 agonists mediated by oxidative stress.
Publications
- Impact of prophylactic CpG Oligodeoxynucleotide application on implant-associated Staphylococcus aureus bone infection. Bone. 2015 Sep;78:194-202
Sethi S, Thormann U, Sommer U, Stötzel S, Mohamed W, Schnettler R, Domann E, Chakraborty T, Alt V
(See online at https://doi.org/10.1016/j.bone.2015.04.030) - TLR9 mediates S. aureus killing inside osteoblasts via induction of oxidative stress. BMC Microbiology 2016, 16:230
Mohamed W, Domann E, Mannala G, Lips KS, Chakraborty T, Heiss C, Schnettler R, Alt V
(See online at https://doi.org/10.1186/s12866-016-0855-8)
