High Salivary 3-Nitrotyrosine Levels in Periodontitis

Background: Tyrosine, a non-essential amino acid involved in protein biosynthesis, can undergo oxidative modification upon exposure to reactive species like the peroxynitrite radical (ONOO^-), resulting in the formation of 3-nitrotyrosine (3-NT). High concentrations of 3-NT have been found in the periodontal tissues of rats with periodontitis and in one study involving twelve patients with periodontitis; further, a correlation between 3-NT concentrations in periodontal tissues and clinical indices of periodontitis was found in 24 patients with periodontitis. The objectives of our study were to compare salivary 3-NT concentrations in subjects with and without periodontitis, to determine whether an association exists between salivary 3-NT concentrations and periodontitis, and to evaluate the potential of salivary 3-NT concentrations for the diagnosis of periodontitis. Material and Methods: This prospective study involved the measurement of salivary 3-NT concentrations in individuals diagnosed with periodontitis-defined by the presence of periodontal tissue loss-and in individuals without periodontitis, characterized by either periodontal health or localized gingivitis affecting fewer than 30% of sites. A total of 66 participants without periodontitis and 60 with periodontitis were included. To identify variables independently linked to periodontitis, multivariate logistic regression was applied. Additionally, a receiver operating characteristic (ROC) analysis was carried out to assess the ability of salivary 3-NT levels to discriminate between the two groups. Results: Multivariate logistic regression analysis showed that the variables independently associated with periodontitis were salivary 3-NT concentrations > 4.25 ng/mL (OR = 3.22; 95% CI = 1.180-8.789; p value = 0.02), age (years) (OR = 1.12; 95% CI = 1.064-1.168; p value < 0.001), and being a never smoker (OR = 0.36; 95% CI = 0.129-0.989; p value = 0.048). The area under the curve (AUC) of salivary 3-NT concentrations for the diagnosis of periodontitis was 62% (95% CI = 53-70%; p value = 0.02). Conclusions: Our findings showed that salivary 3-NT concentrations were higher in subjects with periodontitis than in those without, that there is an association between high salivary 3-NT concentrations and periodontitis, and that salivary 3-NT concentrations may be useful for diagnosing periodontitis.