Resumen de Evaluation of the Host Response in Various Models of Induced Periodontal Disease in Mice
Background: The aim of this study is to characterize and evaluate the host response caused by three different models of experimental periodontitis in mice.
Methods: C57BL/6 wild-type female mice were distributed into six experimental groups and sacrificed at 7, 15, and 30 days after the induction of periodontal disease: 1) group C: no treatment control group; 2) group L: periodontal disease induced by ligature; 3) group G-Pg: oral gavage with Porphyromonas gingivalis (Pg); 4) group G-PgFn: oral gavage with Fusobacterium nucleatum + Pg; 5) group I-Pg: heat-killed Pg injected into the palatal mucosa between the molars; and 6) group I-V: phosphate-buffered saline injected into the palatal mucosa. The samples were used to analyze the immune-inflammatory process in the gingival tissue via descriptive histologic and real-time polymerase chain reaction analyses. The alveolar bone loss was evaluated using microcomputed tomography. The data were analyzed using the Kruskal-Wallis test, followed by a post hoc Dunn test and analysis of variance, followed by a Tukey test using a 5% significance level.
Results: Only the ligature model displayed significant alveolar bone loss in the initial period (7 days), which was maintained with time. The group injected with heat-killed Pg displayed significant alveolar bone loss starting from day 15, which continued to progress with time (P <0.05). A significant increase (P <0.05) in the gene expression of proinflammatory cytokines (interleukin-6 and -1ß) and proteins involved in osteoclastogenesis (receptor activator of nuclear factor-?B ligand and osteoprotegerin) was observed in the ligature group on day 7.
Conclusion: The ligature and injection of heat-killed Pg models were the most representative of periodontal disease in humans, whereas the oral gavage models were not effective at inducing the disease under the experimental conditions.
Periodontitis is an infectious disease characterized by a chronic inflammation of the periodontium and is mediated and modulated by the host immune system.1 The disease involves the apical migration of epithelium and alveolar bone loss. It is considered the most prevalent form of bone pathology in humans.2 Several microorganisms play a pivotal role in periodontitis pathogenesis. Considerable attention has been given to Porphyromonas gingivalis (Pg), a Gram-negative black-pigmented bacterium known to be associated with chronic periodontitis3-5 and its damage to periodontal tissues.6,7 Previous studies4,8 demonstrated that Fusobacterium nucleatum (Fn) is also commonly observed in deep periodontal pockets and is positively correlated with the progression of periodontal disease. This bacterium participates in both adhesion and coaggregation with many other oral bacteria, such as Pg, acting as a bridge between early and late colonizers8 that elicit bone breakdown.9 Various animal models have been used to investigate the host�bacteria interaction and to evaluate the pathogenesis of periodontitis.1,10-13 Animal models of periodontal disease have contributed new knowledge to the biologic sciences. An important feature of the experimental models used to study human infectious diseases is the ability to simulate an infectious process similar to that observed in humans while mimicking the pathogenesis of the natural disease.14 Animal models allow the study of defined aspects of periodontitis, such as the etiology, the role of specific virulence factors, the effect of cells and mediators on tissue responses, the colonization mechanisms, and the role of other infections.14 Mice models of periodontal disease play an important role compared to rat models, especially given the ability to manipulate their genetic characteristics and increase the potential for study interpretations and allowing the study of specific cells or molecules in the development and progression of periodontal disease.1 Longitudinal studies of periodontitis in humans present some limitations related to the mechanisms of disease because of many variables that are difficult to control among patients, such as activity level, progression, susceptibility, and duration of the disease.15 Thus, human studies are limited by the difficulty of elucidating the pathogenesis of periodontal disease.
To initiate experimental periodontal disease in rodents, ligature is one of the most widely used models in periodontal research. In rats, alveolar bone loss occurs predictably after 7 days.16,17 This model is dependent on the presence of bacteria because it has been demonstrated that in germ-free rats, ligatures do not induce significant alveolar bone breakdown.18 A limitation of this model is the mechanical injury caused during the placement of a ligature that could aggravate periodontal tissue breakdown and physiologic bone remodeling.19,20 Another model used involves the localized injection of bacteria or a pathogen component (e.g., lipopolysaccharide [LPS]) into the palatal gingival tissue. This method promotes significant periodontal inflammation that is characterized by an increased expression of inflammatory cytokines, such as interleukin-1ß (IL-1ß), IL-6, and tumor necrosis factor-a, apical migration of the junctional epithelium, and osteoclastogenesis activation, resulting in tissue breakdown.21-23 Oral gavage models have been used in an attempt to reproduce the chronic bone loss observed in periodontal diseases. An experimental model of periodontitis was developed that involves introducing Pg into rats to induce the breakdown of alveolar bone.24-27 This model has also been used with other bacterial strains22 and with mixtures of several bacteria species to evaluate polymicrobial periodontal disease.12,13 In this model, significant bone loss typically takes longer than 4 weeks after the last inoculation.
The variability of the models found in the literature often prevents a direct comparison between the results and conclusions of the studies. Therefore, studies that comparatively assess the disease progression as well as the cellular and molecular characteristics of different periodontitis models can be useful in selecting the appropriate model to be used and in the interpretation of the results obtained in previous studies. Thus, the aim of this study is to characterize and evaluate the host response caused by three different models of experimental periodontitis in mice. To the best of the authors� knowledge, no previous studies have compared these three methods together at a molecular and morphometric levels in periodontal tissues.
