Occurrence of spontaneous periodontal disease in the SAMP1/YitFc murine model of Crohn disease

Abstract

Background: Oral involvement is often associated with inflammatory bowel disease (IBD). Recent evidence suggests a high incidence of periodontal disease in patients with Crohn disease (CD). To the best of the authors' knowledge, no animal model of IBD that displays associated periodontal disease was reported previously. The aim of this study is to investigate the occurrence and progression of periodontal disease in SAMP1/YitFc (SAMP) mice that spontaneously develop a CD-like ileitis. In addition, the temporal correlation between the onset and progression of periodontal disease and the onset of ileitis in SAMP mice was studied.

Methods: At different time points, SAMP and parental AKR/J (AKR) control mice were sacrificed, and mandibles were prepared for stereomicroscopy and histology. Terminal ilea were collected for histologic assessment of inflammation score. Periodontal status, i.e., alveolar bone loss (ABL) and alveolar bone crest, was examined by stereomicroscopy and histomorphometry, respectively.

Results: ABL increased in both strains with age. SAMP mice showed greater ABL compared with AKR mice by 12 weeks of age, with maximal differences observed at 27 weeks of age. AKR control mice did not show the same severity of periodontal disease. Interestingly, a strong positive correlation was found between ileitis severity and ABL in SAMP mice, independent of age.

Conclusions: The present results demonstrate the occurrence of periodontal disease in a mouse model of progressive CD-like ileitis. In addition, the severity of periodontitis strongly correlated with the severity of ileitis, independent of age, suggesting that common pathogenic mechanisms, such as abnormal immune response and dysbiosis, may be shared between these two phenotypes.

Keywords: Crohn disease; animal; inflammatory bowel diseases; models; periodontal diseases; periodontitis..

Figure 1

A) Stereomicroscopy images showing ABL in SAMP and AKR mice at 4, 12, and 27 weeks of age. B) A heat map is a graphical way of displaying a table of numbers by using colors to represent numerical values. Specifically, low severity scores tend toward lighter colors, whereas high severity scores are represented by darker colors. The heat map herein shows single-tooth and total ABL, ABL ratios, and ileum score for each sample in both strains, thus summarizing the relations of periodontal disease to ileal inflammation severity. Each row represents samples from a single animal, with AKR mice clustered in the top half of the picture and SAMP mice in the bottom. Darker colors occur more frequently in the bottom half (SAMP mice), thus representing higher severity scores of both periodontal disease and ileitis in SAMP mice compared with AKR mice. C) Ileal sections from 27-week-old SAMP mice and AKR control mice (H&E; magnification ×10). SAMP mice develop spontaneous, transmural inflammation of the terminal ileum characterized by discontinuous inflammatory infiltrates, villous architecture alterations, and bowel wall thickening, with hypertrophy of the muscular layers, villous blunting and distortion, and infiltration of acute and chronic immune cells. A normal structure in uninflamed control AKR mice is also shown. D) Comparison of tooth axis of left/right M1 and M2 showed no statistical difference between strains (ANOVA), thus indicating similar tooth dimensions in the two strains. LF = left; RG = right.

Figure 2

A) ANOVA of ABL on M1, M2, and M1+M2 according to age. M1 alone was able to discriminate the strains by 12 weeks of age, M1+M2 ABL only at 27 weeks, and M2 alone was not able to identify differences between strains. NS = not significant. B) Regression analysis of ABL in SAMP and AKR mice. SAMP mice showed a comparable ABL value in both sides of the mouth, suggesting a very reproducible model (R² = 0.834); AKR did not show the same features. C) ROC analysis ofM1 ABL and M1 ABL ratio showed high sensitivity to differentiate between the groups, with SAMP AUC = 0.873 and AKR AUC = 0.932. SE = standard error. D) A positive significant correlation between ileal disease and periodontal disease was found in SAMP mice (P = 0.002; R² = 0.432). The severity of periodontal disease was directly related to the severity of ileal damage.

Figure 3

A) Sagittal mandibular sections of SAMP and AKR mice at 4 and 30 weeks of age. Selected areas of interest (black squares) are presented as magnified images below the corresponding section. No notable alveolar bone resorption or signs of inflammation were observed at 4 weeks in either strain. Thirty-week-old SAMP mice showed reduction in the thickness of the alveolar bone crest compared with AKR mice (filled arrows). Surprisingly, severe hypercementosis was found in SAMP mice but not in AKR mice (open arrows) (H&E; original magnification ×10). B) Higher magnification (×40) of the CEJ area shown in Fig. 3A reveals the major thickness of cementum layer (C). PMN and MN cells were present in the periodontal ligament (PDL) layer of SAMP mice. The alveolar bone crest (AB) was markedly reduced in SAMP mice but not in AKR mice at 30 weeks of age. Root dentin (D) appears normal. (H&E stain.) C) Hypercementosis in SAMP mice was accompanied by severe apical lesions (dotted circles) in the absence of apparent endodontic causes. Magnification of apical lesions is shown under the corresponding original image. Numerous inflammatory cells surround the apical region, and alveolar bone remodeling was visible between the roots (H&E; original magnification ×10). D) Ranked Kruskal-Wallis one-way ANOVA showed statistical differences in terms of alveolar bone crest area (ABC) (P = 0.02) and cementum area (P = 0.001) only at 30 weeks of age. NS = not significant.