OR29 - Role of Oxidative Stress in Chronic Periapical Lesions

Abstract: Apical periodontitis is an immune-inflammatory reaction to endodontic infection associated with disturbed redox signaling. This study aimed to characterize the oxidative parameters of periapical granulation tissue associated with persistent apical periodontitis at two different stages of the disease activity (chronic lesions exhibiting acute exacerbation versus chronically inflamed lesions). A retrospective analysis of human periapical tissue samples (n=20, 10: acute exacerbation of chronic lesions, 10: chronic lesions) obtained during apical surgery of single-rooted endodontically treated teeth with persistent apical periodontitis was conducted. Diagnoses were confirmed by two oral pathologists (MM, AA) based on histopathological findings. Tissue samples were processed for immunohistochemical staining to evaluate the expression of NADPH oxidase (NOX2, a pro-oxidant enzyme), catalase (an antioxidant enzyme), and CD45, a pan-leukocyte marker that regulates the immune response during inflammation, using anti-gp91-phox, anti-catalase, and anti-CD45 conjugated antibodies, respectively. Significantly higher levels of NOX2 and catalase were detected in chronic lesions with acute exacerbation compared to chronically inflamed lesions (p <.01). Comparable ratios of NOX2 and catalase to CD45-positive cells were detected in both conditions (p>.05). The ratio of expression of catalase to NOX enzymes was higher in chronic lesions (1.43) compared to acute exacerbation lesions (1.32), with a 29.3% increased expression of CD45 in the latter (p>.05).Acute exacerbation of chronic apical granulation tissue lesions is characterized by higher levels of pro- and antioxidant enzymes (NOX2 and catalase) compared to chronic lesions, highlighting the role of the host immune response to localize the infection and prevent further apical tissue breakdown.