Epithelial Inflammatory iNOS–Nitrate Axis Enhances P. gingivalis Pathogenicity via V. parvula in Diabetes-Associated Periodontitis

The mechanisms by which host inflammatory responses reshape the pathogenic potential of oral microbiota in mucosal inflammatory diseases remain poorly defined. Metagenomic sequencing of subgingival plaque and single-cell RNA sequencing of gingival tissues were performed in patients with diabetes-associated periodontitis (DP) and non-diabetic periodontitis (P). A diabetic mouse model was used to evaluate inflammation and bone resorption following oral inoculation with Porphyromonas gingivalis (P. gingivalis), Veillonella parvula (V. parvula), or both. Human gingival epithelial cells (HGECs) were cultured under high glucose conditions with or without an iNOS inhibitor 1400 W to assess iNOS and nitrate levels. A P. gingivalis–V. parvula co-culture system with nitrate supplements was used to evaluate P. gingivalis growth and virulence. Higher abundance of P. gingivalis and V. parvula was found in DP subgingival plaque. In diabetic mice, these bacteria worsened bone resorption and increased iNOS+ epithelial cells. Single-cell sequencing showed higher iNOS expression in DP patients, linked to V. parvula. In vitro, high glucose increased iNOS and nitrate in HGECs, and these effects were reversed by 1400 W. With V. parvula, nitrate over 200 μM enhanced P. gingivalis growth and virulence. Diabetic epithelial iNOS-derived nitrate boosts P. gingivalis pathogenicity through V. parvula, worsening periodontal inflammatory bone damage.