Abstract: Objective · To investigate whether methylene blue-mediated photodynamic therapy (MB-PDT) can induce the apoptosis of macrophages in periodontitis, and simultaneously reduce the bone absorption. Methods · For in vitro treatments, cells were divided into three experimental groups: control group, no treatment; MB group, methylene blue treatment; MB-PDT group, MB and laser irradiation treatment. Then apoptosis and apoptosis related genes were detected in each group. For in vivo treatments, periodontal disease in SD rats was orthodontic ligature and periodontal pathogen induced at the first maxillary molar. After 6 weeks, the ligature was removed and all animals received scaling and root planning(SRP) and were divided according to the following treatments: SRP group, saline solution; MB group, phenothiazinium dye; and MB-PDT group, MB and laser irradiation, once a week. All animals in each treatment were killed after 3 weeks. Immunofluorescence and Micro CT analyses were used to detect the apoptotic macrophages and alveolar bone resorption in periodontal tissues of rats in each group. Results · In vitro experiments showed that the combination of 10 μmol/L MB and 40 J/cm2 light dose could kill more than 50% macrophages, and the apoptosis of macrophages inducedMB-PDT in this mode was most obvious. Meanwhile, MB-PDT increased the ratio of proapoptotic gene Bax /antiapoptotic gene Bcl-2 in macrophages. In vivo experiments showed that the macrophages infiltrated in tissues with periodontitis were apoptotic after MB-PDT treatment, while no obvious apoptosis of macrophages infiltrated in the periodontal tissues of SRP and MB rats was found. Micro CT analysis showed that the alveolar bone resorption in MB-PDT rats was less than that in SRP and MB rats (P<0.05), and there was no significant difference between SRP rats and MB rats. Conclusion · MB-PDT can induce the apoptosis of hyperproliferating macrophages in periodontitis and reduce the bone absorption. Compared with SRP, MB-PDT is an effective adjunctive treatment of periodontitis.

Key words: periodontitis, apoptosis, methylene blue, photodynamic therapy, macrophages