Subinhibitory concentrations of tetracyclines induce lipopolysaccharide shedding by Porphyromonas gingivalis and modulate the host inflammatory response

Background and Objective Antibiotics at below minimal inhibitory concentrations ( MIC s) may induce various biological responses in bacteria. In this study, we hypothesized that subinhibitory concentrations (sub IC s) of tetracycline and doxycycline induce the shedding of lipopolysaccharide ( LPS ) by Porphyromonas gingivalis and, as a consequence, may contribute to enhancing the host inflammatory response associated with periodontitis. Material and Methods A polymyxin‐based enzyme‐linked immunosorbent assay was used to quantify LPS shedding by P. gingivalis grown in the presence of sub IC s of tetracycline and doxycycline. A macrophage model was used to show that tetracycline‐ and doxycycline‐mediated LPS shedding by P .  gingivalis can induce cytokine secretion. The secretion of interleukin (IL)‐1β, IL ‐8, and tumor necrosis factor‐α was quantified by enzyme‐linked immunosorbent assay . Results LPS was shed spontaneously in a time‐dependent way by P. gingivalis during growth. LPS shedding was significantly increased by growth in the presence of subICs of tetracycline and doxycycline corresponding to 1/20 of their MICs (0.025 μg/mL for tetracycline and 0.0125 μg/mL for doxycycline). This shedding was not associated with an increased rate of bacterial cell lysis. Stimulating macrophages with a P. gingivalis culture supernatant induced the secretion of IL‐1β, IL‐8 and tumor necrosis factor‐α when the bacteria were grown in the presence of 1/20 MIC of the antibiotics. Conclusion Our study showed that growing P. gingivalis in the presence of sub IC s of either tetracycline or doxycycline induces LPS shedding. Shed LPS may in turn increase cytokine secretion in a macrophage model.