Effects by periodontitis on pristane-induced arthritis in rats

Abstract

Background: An infection-immune association of periodontal disease with rheumatoid arthritis has been suggested. This study aimed to investigate the effect of pre-existing periodontitis on the development and the immune/inflammatory response of pristane-induced arthritis.

Methods: We investigated the effect of periodontitis induced by ligature placement and Porphyromonas gingivalis (P. gingivalis) infection, in combination with Fusobacterium nucleatum to promote its colonization, on the development of pristane-induced arthritis (PIA) in rats (Dark Agouti). Disease progression and severity of periodontitis and arthritis was monitored using clinical assessment, micro-computed tomography (micro-CT)/intraoral radiographs, antibody response, the inflammatory markers such as α-1-acid glycoprotein (α-1-AGP) and c-reactive protein (CRP) as well as cytokine multiplex profiling at different time intervals after induction.

Results: Experimentally induced periodontitis manifested clinically (P < 0.05) prior to pristane injection and progressed steadily until the end of experiments (15 weeks), as compared to the non-ligated arthritis group. Injection of pristane 8 weeks after periodontitis-induction led to severe arthritis in all rats demonstrating that the severity of arthritis was not affected by the pre-existence of periodontitis. Endpoint analysis showed that 89% of the periodontitis-affected animals were positive for antibodies against arginine gingipain B and furthermore, the plasma antibody levels to a citrullinated P. gingivalis peptidylarginine deiminase (PPAD) peptide (denoted CPP3) were significantly (P < 0.05) higher in periodontitis rats with PIA. Additionally, there was a trend towards increased pro-inflammatory and anti-inflammatory cytokine levels, and increased α-1-AGP levels in plasma from periodontitis-challenged PIA rats.

Conclusions: Pre-existence of periodontitis induced antibodies against citrullinated peptide derived from PPAD in rats with PIA. However, there were no differences in the development or severity of PIA between periodontitis challenged and periodontitis free rats.

Keywords: Arginine gingipain; Citrullinated peptide; Cytokine; Inflammation; Peptidylarginine deiminase; Periodontitis; Porphyromonas gingivalis; Pristane-induced arthritis.

Fig. 1

Clinical manifestation of periodontitis and radiographic assessment of bone loss. a Intraoral photograph of the ligated second upper molar in a rat with arthritis and experimental periodontitis. b Radiograph image of bone volume around a second upper molar, c micro-CT data (horizontal section) indicating bone loss around the upper molars and d, e 3D rendering of micro-CT data of bone volume around maxillary molars in an arthritis rat with experimental periodontitis. f Intraoral photograph of the non-ligated second upper molar of an arthritis rat without induced periodontitis. g Radiograph image of bone volume around the second upper molar, h micro-CT data (horizontal section) indicating bone loss around the upper molars and i 3D rendering of micro-CT data of bone volume around maxillary molars in a rat without induced periodontitis. j Mean tooth mobility score (±SE) in arthritis rats with periodontitis (n = 9) and without periodontitis (n = 12) throughout the experimental period of 15 weeks. k Distribution of mean alveolar bone level at endpoint in arthritis rats with periodontitis (n = 8) and without periodontitis (n = 10). ^*P < 0.05 was considered statistically significant. Circle indicates outliers. Gray line indicates time point of pristane injection. PIA pristane-induced arthritis, PA rats with experimental periodontitis and PIA, A rats with PIA without periodontitis

Fig. 2

Effect of pre-existing periodontitis on weight changes, arthritis disease severity and α-1-AGP levels. a Mean changes in weight (grams ± SE) in arthritis rats with and without periodontitis throughout the experimental period of 15 weeks. b Mean arthritis disease severity score (±SE) of front and hind paws in arthritis rats with and without periodontitis, up to 7 weeks after pristane injection. c Mean plasma concentrations (μg/ml ± SE) of α-1-AGP in arthritis rats with and without periodontitis throughout the experimental period of 15 weeks. The results are presented as mean values (±SE) for the groups PA (n = 9) and A (n = 12) at different time-points throughout the experiment. Gray line indicates time point of pristane injection. PIA pristane-induced arthritis, PA rats with experimental periodontitis and PIA, A rats with PIA without periodontitis

Fig. 3

Micro-CT images and visual appearance of front and hind paws for assessment of arthritic changes. Micro-CT images of bone and tissue changes in front and hind paws of animals affected with experimental periodontitis and induced arthritis (PA), arthritis without periodontitis (A) and corresponding images of DA rats without induced arthritis or periodontitis (Healthy) at the time-point of 15 weeks; and visual appearance of front and hind paws at endpoint

Fig. 4

Plasma RgpB, CPP3 and RPP3 levels. Mean plasma concentrations (AU/ml ± SE) of antibodies against a RgpB, b CPP3 and RPP3 in arthritis rats with and without periodontitis and healthy control animals at endpoint of the experimental period of 15 weeks. *P < 0.05 was considered statistically significant. PA rats with experimental periodontitis and PIA (n = 9), A rats with PIA without periodontitis (n = 12), Healthy control rats without induced arthritis or periodontitis (n = 4), RgpB arginine gingipain B, CPP3 citrullinated peptide derived from PPAD, RPP3 arginine-containing (uncitrullinated) PPAD peptide