Effects of Non-Surgical Periodontal Therapy on Gingival Crevicular Fluid Apelin Isoforms and Oxidative Stress Markers in Periodontitis

Background/Objectives: Periodontitis is a chronic inflammatory disease in which host response and oxidative stress contribute to periodontal tissue destruction. Apelin isoforms may be involved in inflammatory regulation, tissue remodeling, and oxidative balance. This study evaluated changes in gingival crevicular fluid (GCF) apelin-13, apelin-36, total antioxidant status (TAS), total oxidant status (TOS), and oxidative stress index (OSI) following non-surgical periodontal therapy (NSPT) in systemically healthy individuals with stage I–II or stage III–IV periodontitis. Methods: A total of 61 systemically healthy individuals with periodontitis were included and divided into two groups: stage I–II periodontitis (n = 31) and stage III–IV periodontitis (n = 30). Clinical periodontal parameters and GCF samples were obtained at baseline and at 1, 3, and 6 months after NSPT. Apelin-13 and apelin-36 levels were measured by enzyme-linked immunosorbent assay, while TAS and TOS levels were determined using commercial assay kits. OSI was calculated as the percentage ratio of TOS to TAS. The study was retrospectively registered at ClinicalTrials.gov (NCT06850987). Results: Baseline apelin-13 levels were significantly higher in stage III–IV periodontitis and decreased in both groups after NSPT, whereas apelin-36 increased over time and was higher in stage I–II periodontitis at baseline. Apelin-13 was positively associated with clinical periodontal parameters, while apelin-36 showed negative associations. TAS remained higher in stage I–II periodontitis, whereas OSI was consistently higher in stage III–IV periodontitis. Conclusions: These findings suggest that the combined assessment of GCF apelin isoforms and oxidative stress markers may provide useful biomarker information for distinguishing periodontitis severity and monitoring biochemical responses to NSPT.