Plasma RANKL level is not a reliable marker to monitor the bone destruction in mice model of osteomyelitis

Abstract

Objectives: In this experimental study, we aimed to investigate the specific value of receptor activator of nuclear factor kappa-Beta ligand (RANKL) plasma level in osteomyelitis to show the bone destruction and to determine its correlation with classical markers of infection in mice model of osteomyelitis. Materials and methods: Sixty Balb/c female mice (30 to 40 g weight, 3.5 to 4 month-old) were divided into two groups: Controls (n=15) and study group (n=45). All mice underwent tibial decortication and received an injection of sclerosing agent into the intramedullary cavity. The next process was proceeded in two steps to observe the detectability of osteomyelitis-induced bone destruction (step 1) and treatment response (step 2) using the variables examined in our study. In step 1, the study group received 1 mL solution containing Staphylococcus aureus (S. aureus) bacteria (2 yen 108 per mL) into the intramedullary cavity. Five mice from each group were sacrificed every seven days for three weeks and tibia and blood samples were obtained. In step 2, the remaining 30 infected mice were further divided into two groups to investigate the possible value of RANKL plasma level as a marker of treatment response. Fifteen of these mice received teicoplanin 20 mg/kg for four weeks, while the rest did not receive antibiotics. Eight mice from each group were sacrificed at the end of the second week and the remaining 14 mice were sacrificed at the end of four weeks. Complete blood count, procalcitonin level, C-reactive protein (CRP), and RANKL concentrations were measured from blood samples of each sacrificed mouse. Results: Median RANKL concentration of the control subjects was significantly higher than recipients of intervention at the first and third weeks in step 1 where bone destruction of osteomyelitis was examined. No significant changes occurred in groups receiving and not receiving antimicrobial treatment in terms of RANKL, CRP, and procalcitonin levels throughout four weeks in step 2. The RANKL concentration was significantly correlated with colony growth in subjects allocated to the S. aureus inoculation group (r=-0.547, p=0.035). Conclusion: The RANKL levels in mice with S. aureus osteomyelitis are not correlated with colony growth or other markers of inflammation and not useful for monitoring the response to antimicrobial treatment during osteomyelitis.