Abstract: BACKGROUND: Previous studies showed that immunomodulatory peptide DP7 has good antibacterial activity and immunomodulatory activity in vitro.  
OBJECTIVE: To investigate the therapeutic effect of a new type of immunoregulatory peptide DP7 temperature-sensitive gel on periodontitis in rats.
METHODS:  The periodontitis model of right maxillary first molar was established in 8-week-old SD rats, and the 48 successfully modeled rats were divided into 6 groups. Except for the natural healing group without treatment, minocycline hydrochloride was injected into periodontal pocket of positive control group. The periodontal pocket of the rest of the four groups were injected with regulatory peptide DP7 concentration 0% (blank gel), 0.1%, 0.3%, 1% temperature-sensitive gel, once a week for 4 weeks. Four weeks later, the periodontal probing depth and the distance between cementum enamel boundary and alveolar crest were examined; and histological and immunohistochemical staining of the right maxilla was performed.  
RESULTS AND CONCLUSION: (1) The probing depth and the distance between cementum enamel boundary and alveolar crest in 1% and 0.3% DP7 gel treatment groups were lower than those in positive control group (P < 0.05). (2) Hematoxylin-eosin staining showed that the gingival tissue of 0.1%, 0.3%, 1% DP7 gel groups and positive control group was more complete, and the epithelial pedicle process returned to normal, with the orderly array of fibroblasts and new capillaries, and no obvious osteoclasts were observed. The blank gel treatment group and the natural healing group showed the pathological manifestations of periodontitis. (3) Masson staining showed that a large number of new fibroblasts were orderly arranged in the 0.1%, 0.3%, and 1% DP7 gel groups and the positive control group, and bulging collagen hyperplasia and new capillaries were visible. Osteoid or new bone formation was even observed in the 1% and 0.3% DP7 gel groups. However, the blank gel group and the natural healing group had no obvious collagen fiber proliferation and osteoid formation. (4) Immunohistochemical staining showed that the expression levels of tumor necrosis factor-α and interleukin-1β in 0.3% and 1% DP7 gel groups were not significantly different from those in the positive control group (P > 0.05). The expression levels of interleukin-10, bone morphogenetic protein-2 and osteoblast specific transcription factor 2 in 0.3% and 1% DP7 gel groups were higher than those in the positive control group (P=0.000). The expression levels of interleukin-10, bone morphogenetic protein-2 and osteoblast specific transcription factor 2 in 0.3% DP7 gel group were higher than those in the 1% DP7 gel group (P < 0.05). (5) The results showed that 0.3% and 1% immunoregulatory peptide DP7 gel had favorable therapeutic effect on periodontitis, and 0.3% immunoregulatory peptide DP7 gel had the best therapeutic effect.

Key words: material, immunomodulatory peptide, temperature sensitive gel, delayed release gel, periodontitis