(P27-044-24) Impact of the Host Metabolite Nitrate on Oral Health and Disease

Objectives: Diet and metabolic status, such as diabetes-induced hyperglycemia, shape the ecological balance between commensals and pathogens in the oral microbiome. In turn, an imbalanced oral microbiome can contribute to gum inflammation (periodontitis) and systemic comorbidities, including diabetes. One of the most abundant small molecules in the oral cavity is the host metabolite nitrate, a microbe-specific nutrient that allows some microbes to respire anaerobically. Nitrate can derive from a healthy diet (e.g., leafy greens) or inflammation, particularly inducible nitric oxide synthase (iNOS) expression. However, whether the source of nitrate differentially impacts oral microbiome-host symbiosis remains obscure. We hypothesize that dietary nitrate promotes oral health, while inflammatory nitrate promotes oral disease.

Methods: We developed a reductionist community comprising the nitrate-respiring oral commensal Neisseria mucosa (Nm) and the periodontal pathogen Fusobacterium nucleatum (Fn). To model dietary nitrate, we cultured Nm and/or Fn as biofilms on media ± nitrate (10 mM). To model inflammatory nitrate, we inoculated mice with Nm and/or Fn to form subcutaneous abscesses. To model type 1 diabetes, we intraperitoneally injected mice with streptozotocin (70 mg/kg per dose).

Results: In the biofilm model, nitrate addition to mono-cultures promoted Nm, while not affecting Fn. In contrast, nitrate addition to co-cultures drove Nm to inhibit Fn. To determine the mechanism, we used Neisseria mutants in the nitrate respiration pathway, revealing that a major byproduct - nitrite - is directly responsible for Fn inhibition. In contrast, Fn was not recoverable from abscess mono-infections, but highly abundant in co-infections with Nm. Co-infection also increased the abundance of iNOS-expressing neutrophils, suggesting a role for neutrophil-derived nitrate in Fn expansion. Lastly, blood glucose levels positively correlated with the abundance of iNOS-expressing neutrophils in Nm-infected abscesses.

Conclusions: Depending on the source of nitrate, nitrate-respiring commensals may promote oral health or disease, including within the context of diabetes.

Funding Sources: NIDCR, NHLBI