| Background:Periodontal diseases are chronic inflammatory diseases that lead eventually to loss of the supporting structures of the teeth,including resorption of the alveolar bone of the jaw. Periodontal diseases are the most prevalent of the diseases of the bone resorption in humans. The cytokines are considered most frequently as active promoters of resorption process. Thus cytokines is not only generally thought of as an immune factor, but it can be taken as the initial process of bone resorption. The gingival cytokines such as tumor necrosis factor-α(TNF-α), interleukin-8(IL-8) and Prostaglandin E2 (PGE2) profile in periodontal disease includes the presence of resorptive cytokines and is key stimulator of bone resorption. However the influence of hypoxia and high altitude environment on the expression of cytokines in periodontium as well as bone resorption in humans is not clear. So it is helpful for us to modulating inflammation and minimizing soft tissue destruction and bone resorption by investigating the pathophysiological process of periodontitis in patients in high altitude area especially in China's Tibet region.Objective:To investigate the expression and concentrations of inflammatory cytokines(TNF-α,PGE2 and IL- 8)in gingival crevicular fluid(GCF) in a rat model of periodontitis exposed to hypoxia at high altitude, and the relationship between cytokines and clinical index for periodontitis was evaluated too.Materials and methods:AnimalsEighty SD rats (200–250 g) were randomly assigned to four of the following groups: the hypoxia group (n=20), the hypoxia control group (n=20), the normoxia group (n=20) and the normoxia control group (n=20). After that the hypoxia group and the hypoxia control group were raised under general hypoxia(simulating the altitude 5000 meters, 23h per day) for 8 weeks ,while the normoxia group and the normoxia control group were raised under normoxia environment separately. And then the rats were sacrificed and analyzed. All experiments were conducted in accordance with the National of Health guidelines for the welfare of experimental animals.Pathological assay, HE staining and immunohistochemical stainingHistological assessment was carried out routine hematoxylin and eosin staining. Pathological assay and HE staining were used to detect the general conditions and pathological changes of rat periodontal tissues. and immunohistochemical staining was conducted to determine the expressions of TNF-α,PGE2 and IL- 8 in different groups.Cytokine quantification by enzyme linked immunosorbent assay (ELISA)GCF sampling was isolated with cotton wool rolls to decrease the risk of salivary contamination. And ELISA assays weas used for detectiong the concentrations of PGE2, TNF-αand IL- 8 in GCF volume.ResultHistologic change and clinical index differencesThe specimens taken from the anoxia group were infiltrated with a significant inflammatory cell and fibroblasts, and showed a significant loss of connective tissue attachment and resorption of alveolar bone compared with the other groups. The index of periodontitis and bone resorption such as attachment lost (AL), plaque index (PLI) and bleeding index (BI) were recorded in each groups. There were significant difference in index between each groups (P<0.05).Histologic and immunohistochemical stain observationImmunohistochemical stain observation showed that the expression of TNF-α, PGE2 and IL–8 were located in cytoplasm in four rats groups. While the expression of TNF-α,PGE2 and IL–8 in the anoxia group were significantly higher than the hypoxia control group(P<0.05) and the normoxia group (P<0.05).Cytokine quantificationCytokine quantification was measured in the volume of collected GCF sample and there was significant difference among the four groups. Anoxia group revealed much higher TNF-αand PGE2 levels than normoxia group (P < 0.01). While the level of IL–8 in anoxia group was lower than normoxia group (P< 0.01). GCF total amount of TNF-αand PGE2 exhibited significant positive correlations with clinical periodontal measurements such as AL,PLI,BI (P < 0.05). Conversely, the amount of IL–8 exhibited significant negative correlations with clinical periodontal measurements such as AL,PLI (P< 0.01), and exhibited no correlations with BI (P>0.05) .Conclusion:1. In our experiments, the successful rat's periodontitis model under simulated high altitude hypoxia environment was established. In our model, the influence of hypoxia and high altitude environment can accelerate and aggravate the pathophysiological process of periodontitis.2. At a simulated altitude of 5,000 meters hypoxia environment in our model, the levels of TNF-αand PGE2 increased, while the level of IL–8 decreased, indicating the high altitude and hypoxia environment may influence the expression and secretion of TNF-α, PGE2 and IL–8 in the periodontal tissues.3. In our simulated high altitude hypoxia environment, TNF-α, PGE2 and IL–8 exhibited significant correlations with clinical periodontal measurements, indicating that the difference of expression and secretion of cytokines, such as TNF-α, PGE2 and IL–8 may modify the micro-environment of periodontal tissues. Ultimately they may induce osteoclast formation and activation, accelerating and aggravating the pathophysiological process of periodontitis and bone resorption in patients in high altitude area.
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