Temporal and spatial effects on C‐reactive protein's regulation of inducible nitric oxide synthase production in periodontal disease

Abstract Background Inducible nitric oxide synthase (iNOS) is associated with inflammation and osteoclastic differentiation in periodontal disease. This study was conducted to compare the time‐dependent variation in iNOS production between the gingiva and other periodontal tissues and to explore the potential association with C‐reactive protein (CRP) in early periodontal disease. Methods Ligature‐induced periodontal disease models (0–14 days) were established in wild‐type and CRP knockout rats. Changes in CRP, iNOS, and autophagy levels were examined in the gingiva and other periodontal tissues. Macrophages were treated with lipopolysaccharide and chloroquine to explore the role of autophagy in iNOS production. iNOS, CRP, and autophagy‐related proteins were analyzed using Western blotting, immunostaining, and enzyme‐linked immunosorbent assays. mRNA expression was detected by quantitative real‐time polymerase chain reaction. Hematoxylin and eosin staining was used for histological analysis. Cathepsin K immunostaining and microcomputed tomography of the maxillae were performed to compare alveolar bone resorption. Results iNOS and CRP levels increased rapidly in periodontal tissues, as observed on Day 2 of ligature, then decreased more rapidly in the gingiva than in other periodontal tissues. CRP deficiency did not prevent iNOS generation, but effectively accelerated iNOS reduction and delayed alveolar bone loss. The CRP effect on iNOS was accompanied by a change in autophagy, which was reduced by CRP knockout. Conclusions The regulation of iNOS by CRP shows temporospatial variation in early periodontal disease and is potentially associated with autophagy. These findings may contribute to the early detection and targeted treatment of periodontal disease.