Effects of hydroxytyrosol on alveolar bone resorption and oxidative stress parameters in experimental periodontitis of rats

Hydroxytyrosol (HT) is a polyphenol compound which has mainly antioxidant activity and also possesses other cytoprotective properties with beneficial health effects. These include anti-inflammatory, anticancer, endothelial and vascular function improvement. In addition it has been reported that HT can decrease alveolar bone loss. Therefore, HT has crucial effects on molecular and cellular alterations associated with chronic diseases and becomes a potential therapeutic agent for the prevention and/or treatment. The aim of this study was to determine the effects of systemically administered HT on experimental periodontitis (EP) in rats. Thirty two rats were divided randomly into four groups; 1) periodontally healthy + serum physiologic (PH-SP), 2) periodontally healthy + hydroxytyrosol (PH-HT), 3) experimental periodontitis + serum physiologic (EP-SP) and 4) experimental periodontitis + hydroxytyrosol (EP-HT). Ligatures were placed around maxillary second molars in EP groups. After induction of EP, HT (test) and SP (control) was administered and continued for 14 days. The animals were euthanized on 15th day and the jaws were removed for histopathologic, histomorphometric and immunohistochemical analyses. Enzyme-linked immunosorbent assay (ELISA) was used to analyse serum and tissue malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) levels. The receptor activator of NF-kB ligand (RANKL), osteoprotegerin (OPG) levels and RANKL/OPG ratio were analysed via immunolabeling. Analysis of variance (ANOVA)-Tukey and Kruskal Wallis- Mann Whitney U tests were used to analyse the data. Experimental periodontitis groups had significantly more alveolar bone loss compared to the PH groups (p<0.05). On the other hand, the difference between the EP-HT and the EP-SF groups did not reach significance (p>0.05). Serum and tissue MDA, SOD and GSH-Px levels did not differ between EP-HT and EP-SF groups (p>0.05). Beside, tissue SOD levels of PH-HT group were significantly higher than PH-SF group (p<0.05). Immunohistochemical evaluation showed that higher RANKL levels and RANKL/OPG ratio, and lower OPG levels in EP than PH groups (p<0.05). It was found that RANKL levels and RANKL/OPG ratio in HT applied PH-HT and EP-HT groups were significantly lower than SF applied PH-SF and EP-SF groups (p<0.05). Within the limits of this study, it was determined that systemically HT application did not effect serum and tissue MDA, SOD and GSH-Px levels. Decreased RANKL levels and RANKL/OPG ratio in HT groups showed that systemically HT administration might prevent alveolar bone loss, on the other hand, this result was not supported by histomorphometric measurements.