Experimental Study on Anti-Infection and Promotion of Macrophage Polarization for the Treatment of Traumatic Bone...

Traumatic osteomyelitis remains a prevalent and intractable clinical disorder in orthopedics. Treatment of this condition is severely hindered by multiple factors, including multidrug-resistant bacterial infections (predominantly methicillin-resistant Staphylococcus aureus, MRSA), the blood-bone barrier, infection-induced bone necrosis, and the internalization capacity of bone cells. Current therapeutic strategies mainly consist of debridement, systemic antibiotic administration, and local sustained-release antibiotic delivery. Local biodegradable materials with sustained antibiotic release may help maintain effective antibacterial exposure at infectious sites and may be associated with favorable changes in the inflammatory microenvironment during infection resolution and tissue repair.

Our research team has previously constructed rifampicin/moxifloxacin-loaded Poly(lactic-co-glycolic acid) (PLGA) sustained-release microspheres and validated their favorable sustained-release characteristics and antibacterial properties in vitro. In the present study, we further investigated their therapeutic efficacy against traumatic osteomyelitis, with a focus on infection-related pathological changes and macrophage polarization-associated inflammatory responses. A murine femoral traumatic osteomyelitis model was established, and animals were assigned to three groups (control, model, and rifampicin-moxifloxacin (RM)-PLGA treatment) for comparative intervention. General observation, X-ray examination, and histopathological staining were performed for evaluation. Additionally, serological analysis, histopathological assessment, western blotting, and immunofluorescence were used to detect relevant indicators. In vitro experiments using infected RAW264.7 macrophages co-cultured with microspheres were conducted to further verify the effects.

General observation, X-ray examination, and histopathological staining revealed that local infection was markedly alleviated in the microsphere group, whereas persistent infection-related changes were observed in the model group, and the control group remained largely normal. Serological analysis, histopathological assessment, Western blot, and immunofluorescence showed that RM-PLGA treatment attenuated inflammatory responses and was associated with changes in macrophage polarization-associated markers. In vitro, RM-PLGA treatment reduced IL-6 and IL-1β levels, increased IL-10 levels, and significantly decreased the fluorescence intensities of both CD38 and CD206. In vivo, RM-PLGA treatment reduced serum pro-inflammatory cytokine levels and CD38 fluorescence intensity. CD206 fluorescence intensity was comparable to that in the model group on day 7 but was significantly lower on days 14 and 28; serum IL-10 levels were significantly lower on days 7 and 28 and did not differ significantly on day 14. In addition, RM-PLGA treatment was accompanied by changes in the expression of YTHDC1, PDPK1, and PTGS2, suggesting that these molecules may be associated with infection resolution and inflammatory microenvironment remodeling. However, further functional validation is required to confirm their causal roles.

Collectively, these findings suggest that rifampicin/moxifloxacin-loaded PLGA microspheres may represent a promising local therapeutic strategy for traumatic osteomyelitis by alleviating infection-related pathological changes and promoting favorable changes in macrophage polarization markers.