Abstract
This study used in vivo microdialysis to examine the effects of intragingival application of lipopolysaccharide (LPS) derived from Porphyromonas gingivalis (Pg-LPS) on gingival tumour necrosis factor (TNF)-α and interleukin (IL)-6 levels in rats. A microdialysis probe with an injection needle attached to the surface of the dialysis membrane was implanted into the gingiva of the upper incisor. For comparison, the effects of LPS derived from Escherichia coli (Ec-LPS) on IL-6 and TNF-α levels were also analysed. Pg-LPS (1 μg/1 μL) or Ec-LPS (1 or 6 μg/1 μL) was applied by microsyringe, with gingival dialysates collected every hour. Enzyme-linked immunosorbent assay (ELISA) revealed that gingival dialysates contained approximately 389 pg·mL−1 of IL-6 basally; basal TNF-α levels were lower than the detection limit of the ELISA. Pg-LPS failed to alter IL-6 levels but markedly increased TNF-α levels, which remained elevated for 2 h after treatment. Neither IL-6 nor TNF-α were affected by Ec-LPS. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed that the gingiva expresses Toll-like receptor (TLR) 2 and TLR4 mRNA. Immunohistochemical examination showed that TLR2 and TLR4 are expressed by gingival epithelial cells. The present study provides in vivo evidence that locally applied Pg-LPS, but not Ec-LPS, into the gingiva transiently increases gingival TNF-α without affecting IL-6. The present results suggest that TLR2 but not TLR4 expressed on gingival epithelial cells may mediate the Pg-LPS-induced increase in gingival TNF-α in rats.
Highlights
Periodontal disease is a chronic inflammation of the gingiva resulting in the destruction of periodontal tissue[1] and is frequently caused by infection with gram-negative pathogens.[2]
Enzyme-linked immunosorbent assay (ELISA) revealed that gingival dialysates contained approximately 389 pg?mL21 of IL-6 basally; basal tumour necrosis factor (TNF)-a levels were lower than the detection limit of the ELISA
Effects of intragingival injection of LPS on gingival IL-6 and TNF-a measured by in vivo microdialysis Gingival dialysates contained an average of 389 pg?mL21 IL-6 at baseline; basal TNF-a levels were lower than the detection limit of the ELISA kit (5 pg?mL21) (Table 1)
Summary
Periodontal disease is a chronic inflammation of the gingiva resulting in the destruction of periodontal tissue[1] and is frequently caused by infection with gram-negative pathogens.[2]. These findings clearly suggest that locally applied LPS can increase inflammatory mediators at the injection site
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