Periodontal Disease Progress in Lewis Rats

Objectives: Cell-mediated immunity plays a critical role in the pathogenesis of severe periodontitis (PD). OBJECTIVE: Characterize the progress of PD and alveolar bone loss in Lewis rats, a readily-available laboratory strain used to study Th1-mediated autoimmune diseases.
Methods: One group of rats was euthanized at age six wks (BASE, N=8). Two groups were fed standard (STD, N=12) or high sucrose/casein (HSC, N=20) diets beginning at age six wks and euthanized at age 29 wks. Mandibles/maxillae taken at necropsy were processed to assess degree of PDScore [0-4] and alveolar crest height (ACH, mm), at molar (M) interdental regions M1M2 and M2M3, by qualitative histology and MicroCT or histometry, respectively. The expression of genes associated with inflammation (IL-6, IL-1β, RANKL, MMP-9, and TNF-α) and bacterial infection (TLR-2 and TLR-4) was evaluated in separate gingival and alveolar mucosa samples, using quantitative-real-time-PCR. Data were tested for significance by ANOVA and applicable post-hoc test.
Results: PDScore for BASE, STD, and HSC groups were 0.25±0.46, 0.36±0.51, and 1.53±0.87, respectively (Mean±SD). Mandibular M1M2 ACH was 0.55±0.05, 0.56±0.07, and 0.66±0.09; and maxillary M1M2 ACH was 0.27±0.06, 0.31±0.07, and 0.38±0.07 for BASE, STD, and HSC, respectively. Similar, but less marked, ACH trends occurred at M2M3. There were no significant differences between BASE and STD groups. Significantly worse PDScore (P<.0001), mandibular ACH (P<.006) and maxillary ACH (P<.02), and IL-6 expression (P<.05) were observed in HSC than in BASE or STD groups. No other significant differences among groups were found for any other genes or sites.
Conclusions: These findings indicate that by age 29 weeks in Lewis rats: 1) no significant age-related PD develops; 2) modest periodontal inflammation and alveolar bone loss develops during HSC diet consumption. These data, compared to historical data, suggest that HSC diet-related severe PD develops more slowly in Lewis rats than in rice rats (Oryzomys palustris).