The use of rodent models to investigate host-bacteria interactions related to periodontal diseases

Abstract

Even though animal models have limitations, they are often superior to in vitro or clinical studies in addressing mechanistic questions and serve as an essential link between hypotheses and human patients. Periodontal disease can be viewed as a process that involves four major stages: bacterial colonization, invasion, induction of a destructive host response in connective tissue and a repair process that reduces the extent of tissue breakdown. Animal studies should be evaluated in terms of their capacity to test specific hypotheses rather than their fidelity to all aspects of periodontal disease initiation and progression. Thus, each of the models described below can be adapted to test discrete components of these four major steps, but not all of them. This review describes five different animal models that are appropriate for examining components of host-bacteria interactions that can lead to breakdown of hard and soft connective tissue or conditions that limit its repair as follows: the mouse calvarial model, murine oral gavage models with or without adoptive transfer of human lymphocytes, rat ligature model and rat Aggregatibacter actinomycetemcomitans feeding model.

Fig 1

Use of the calvarial model to demonstrate that P. gingivalis-induced osteoclastogenesis in vivo is largely modulated through TNF. P. gingivalis or vehicle alone was inoculated into the scalp of TNFRp55^-/-/p75 ^-/- or control mice. Osteoclasts were identified as TRAP positive multinucleated cells lining bone and quantified from sections taken five days after P. gingivalis inoculation. * indicates p<0.05 for P.g. vs. vehicle alone, ** indicates p<0.05 for TNFR^-/- vs. WT. This figure was previously published in (Graves, et al., 2001).

Fig 2

Control of alveolar bone loss by A. actinomycetemcomitans ( A.a)-reactive CD4⁺T-cells. Groups of mice as indicated were either left untreated or inoculated with A.a. CD4⁺T, CD8⁺T, or B cells were depleted from mice using antibody and complement as described (Teng et al. 2000). Data shown are the mean (± SD) of alveolar bone loss by time up to 8 weeks, expressed as % of bone loss detected in positive control, A.a-infected BALB/c mice (as 100%). Group I, sham-infected, nondepleted NOD/SCID mice (n = 10); group II, A.a-infected, nondepleted HuPBL-NOD/SCID mice (n = 32); group III, A.a-infected, CD4⁺T cell-depleted NOD/SCID mice (n = 20); group IV, sham-infected, CD4⁺T cell-depleted NOD/SCID mice (n = 9); group V, A.a-infected, CD8⁺T cell-depleted NOD/SCID mice (n = 12); group VI, A.a-infected, B cell-depleted NOD/SCID mice (n = 16); group VII, A.a-infected NOD/SCID mice bearing adoptively transferred A.a-reactive CD4⁺T cells (AT-CD4T) plus autologous MO/MQ as APCs (n = 10); group VIII, A.a-infected NOD/SCID mice bearing adoptively transferred autologous MO/MQ as APCs (irr-APC; n = 6). Statistical differences for bone loss between group III and groups II, IV, V, and VI were significant (p<0.005).

Fig 3

Periodontal bone loss in the oral gavage model. Assessment of bone levels is made by measuring the distance from the cementoenamel junction (CEJ) to the alveolar bone crest (ABC) at the seven indicated buccal sites on the three molars on the left side and the symmetrical seven sites on the right side of the maxilla. To determine bone loss, the 14-site total CEJ-ABC distance for each infected mouse is subtracted from the mean CEJ-ABC distance from the group of sham-infected mice. (A) Sham-infected BALB/cByJ mouse (B) P. gingivalis-infected BALB/cByJ mouse demonstrating increased CEJ-ABC distances at the molar sites, compared to sham infection. (C) Sham-infected C57BL/6J mouse (D) P. gingivalis-infected C57BL/6J mouse demonstrating negligible bone loss compared to sham infection, due to genetically-determined resistance to bone loss. Originally published by Baker PJ, Dixon M, Roopenian DC, 2000.

Fig. 4

Time line for studying A. actinomycetemcomitans colonization and bone loss in the rat.

Fig 5

Diabetes inhibits reparative alveolar bone formation following resorption. To induce periodontal bone loss ligatures were placed around the second molar teeth of type 2 diabetic (ZDF) and normoglycemic matched littermates. After 7 days ligatures were removed which allowed coupling to proceed involving the formation of new bone. The amount of bone formed following resorption was significantly less in the diabetic group suggesting that net bone loss may be greater in the diabetic group due to the failure to form new alveolar bone following an episode or resorption. * indicates significant difference between diabetic and normoglycemic control rats (P<0.05). This figure was previously published (Liu, et al., 2006b).