Abstract: PURPOSE: To investigate the effect of chitosan oligosaccharide on alveolar bone resorption, Th17/Treg balance and OPG/RANKL/RANK pathway in rats with periodontitis. METHODS: Rat model of periodontitis was established, and the periodontitis rats were randomly divided into model group, low-dose chitosan oligosaccharide group, middle-dose chitosan oligosaccharide group, high-dose chitosan oligosaccharide group and metronidazole group, with 12 rats in each group, another 12 rats were set as control group. After treatment, gingival index and alveolar bone absorption were evaluated. H-E staining was used to observe the pathological changes of periodontal tissues. The ratio of Th17/Treg cells in peripheral blood was detected by flow cytometry, the levels of serum IL-17, TGF-β, RANKL and OPG were detected by ELISA, and the expressions of OPG and RANKL mRNA in periodontal tissues of rats in each group were detected by real-time fluorescent quantitative PCR(qRT-PCR). SPSS 24.0 software package was used to analyze the data. RESULTS: Compared with the control group, the periodontal tissue of the model group showed periodontal membrane fiber bundle rupture, disordered arrangement, capillary expansion, proliferation, inflammatory cell infiltration and other pathological damage. Gingival index, alveolar bone resorption value, Th17/Treg ratio, serum RANKL and IL-17 levels, and periodontal RANKL mRNA level were significantly increased(P<0.05), while the levels of serum OPG, TGF-β and OPG mRNA in periodontal tissues were significantly decreased (P<0.05). Compared with the model group, the pathological damage of periodontal tissue in the low-middle-and high-dose chitosan oligosaccharide groups and metronidazole group was reduced; gingival index, alveolar bone resorption value, Th17/Treg ratio, serum RANKL and IL-17 levels, and periodontal RANKL mRNA level were significantly decreased(P<0.05), while the levels of serum OPG, TGF-β and OPG mRNA in periodontal tissues were significantly increased(P<0.05); there was a dose-dependent relationship between the chitosan oligosaccharide groups, and there was no significant difference between the high-dose chitosan oligosaccharide group and metronidazole group(P>0.05). CONCLUSIONS: Chitosan oligosaccharide can promote Th17/Treg balance to return to normal, up-regulate OPG expression, down-regulate RANKL expression, inhibit alveolar bone resorption in periodontitis rats and improve their clinical symptoms.

Key words: Chitosan oligosaccharide, Th17/Treg balance, OPG/RANKL/RANK pathway, Periodontitis, Alveolar bone resorption