Nitrate Reduction by Salivary Bacteria and Periodontal Health

Objectives: Nitrate reduction by oral bacteria generates nitrite, which can either be converted to Nitric oxide (NO) via denitrification, or to ammonium via the dissimilatory nitrate reduction to ammonium pathway (DNRA). The choice of pathway can impact systemic NO levels, cardiometabolic health, and also periodontal health.
Objective: To evaluate the association between nitrate metabolism by salivary bacteria and periodontal health.
Methods: A convenience sub-sample of 144 participants from the San Juan Overweight Adult Longitudinal Study (SOALS) was used. Salivary bacteria were incubated with 50mM potassium nitrate under aerobic conditions (N=83) or under CO₂-enriched conditions (GasPak^TM, N=61). Nitrite was measured using the Sievers^TM Nitric Oxide Analyzer NOA 280i (Zysense, NC) and ammonium with the Nessler’s reagent. Nitrate reductase (NR) was defined as nmoles nitrite/min/mg and DNRA as nmoles ammonium/min/mg of protein. Periodontal variables and confounders were available from SOALS. Multivariate analysis was performed using gamma regression or fractional probit regression, depending on the outcome. Models were adjusted for age, sex, plaque index, diabetes, smoking, and type of electron donor used for nitrate reduction (NADP vs. sucrose).
Results: Mean age was 49.8±6.1 years, 63% were females. Mean% of sites with bleeding on probing (%BOP) was 20±22%, probing depth (PD) 1.68±0.47mm, and Clinical Attachment Loss (CAL) 1.60±1.04mm. Under aerobic conditions, DNRA was positively associated with CAL (b=0.03, p=0.024, 95%CI: 0.004, 0.06), and NR was positively associated with %BOP (b_{2nd vs.1st tertile}=0.57, p=0.009, 95%CI: 0.14, 0.99); under CO₂-enrichced conditions, NR was inversely associated with %BOP (b_{2nd vs.1st tertile}=-0.74, p=0.004 , 95% CI: -1.25, -0.24). No other associations between DRNA, NR, and periodontal outcomes were significant.
Conclusions: Nitrate reduction by salivary bacteria can impact periodontal health positively or negatively, depending on conditions that reflect the predominant nitrate-reducing bacteria and pathways. These pathways need to be better characterized to elucidate their role in periodontal and general health.