Background: Subantibiotic doses of doxycycline (lowdose doxycycline [LDD]) have been widely used in periodontal treatment for enzymatic inhibition and related anti-inflammatory properties. The aim of the present study is to verify the possible effects of LDD on oxidative stress in relation to periodontal attachment loss associated with ligature-induced experimental periodontal disease in rats. 

Methods: Thirty female Wistar albino rats were divided into three study groups as follows: 1) control (C) rats; 2) rats with experimental periodontitis (PED); and 3) rats with PED that were treated with doxycycline (PED + LDD). PED was induced by placing ligatures around the cervix of the maxillary second molars for 21 days. The PED + LDD group was treated orally with doxycycline (6 mg/kg) for 21 days after the ligature was placed. After 21 days, the rats were euthanized, and samples of the right maxilla were defleshed and used for histologic and morphometric analyses. The gingival tissue of the left maxilla was used for the analysis of lipid peroxidation (malondialdehyde [MDA]) and antioxidant enzymes (catalase, glutathione peroxidase, and superoxide dismutase). Levels of serum total antioxidant status (TAS)/total oxidant status (TOS) and oxidative stress index (OSI) were also analyzed. 

Results: Alveolar bone loss was significantly higher in the PED group compared with the PED + LDD and C groups (P < 0.05). Doxycycline exhibited the most prominent inhibition on gingival tissue levels of MDA and antioxidant enzymes (P < 0.05). Doxycycline also significantly reduced TOS and OSI levels (P < 0.05) but increased the TAS level. 

Conclusion: Doxycycline helps to prevent periodontal tissue breakdown by inhibiting local and systemic oxidative stress.