Antibiotics Used in Regenerative Endodontics Modify Immune Response of Macrophages to Bacterial Infection

Ciprofloxacin, amoxicillin, and metronidazole are antibiotics used in regenerative endodontic therapy (RET). Although their antimicrobial properties are well-documented, there is a lack of information on the effects of these antibiotics on the immune response by host macrophages and periapical healing. Thus, this study had 2 objectives: (1) to determine the immune response of macrophages to bacterial infection in response to the combination of ciprofloxacin or amoxicillin and metronidazole and (2) using conditioned media produced by these macrophages to simulate the periapical microenvironment, to determine the impact on the expression of extracellular matrix (ECM) components by periodontal fibroblasts. Macrophages were treated with ciprofloxacin and metronidazole or amoxicillin and metronidazole at 10–1000 μg/mL. The treated macrophages were exposed to lipopolysaccharide, and the pro- and anti-inflammatory cytokines produced were quantified with enzyme-linked immunosorbent assay. Periodontal fibroblasts were treated with conditioned media from these treated macrophages, and the expression of ECM genes was determined by quantitative polymerase chain reaction. Lipopolysaccharides elicited the production of proinflammatory cytokines interleukin 1 beta and tumor necrosis factor alpha by macrophages, but this was suppressed by ciprofloxacin and metronidazole. Moreover, only conditioned media from macrophages treated with ciprofloxacin and metronidazole rescued microbial-induced down-regulation of ECM genes by periodontal fibroblasts. Specifically, ciprofloxacin was the antibiotic responsible for these observations. In contrast, these effects were not observed with amoxicillin and metronidazole. Apart from disinfection of the root canal system, the combination of ciprofloxacin and metronidazole also exerts an immunomodulatory effect, which may aid in periapical healing.