Antibacterial efficacy of exogenous nitric oxide on periodontal pathogens

Abstract

Current treatments for periodontitis (e.g., scaling/root planing and chlorhexidine) have limited efficacy since they fail to suppress microbial biofilms satisfactorily over time, and the use of adjunctive antimicrobials can promote the emergence of antibiotic-resistant organisms. Herein, we report the novel application of nitric oxide (NO)-releasing scaffolds (i.e., dendrimers and silica particles) as anti-periodontopathogenic agents. The effectiveness of macromolecular NO release was demonstrated by a 3-log reduction in periodontopathogenic Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis viability. In contrast, Streptococcus mutans and Streptococcus sanguinis, caries-associated organisms, were substantially less sensitive to NO treatment. Both dendrimer- and silica-based NO release exhibited substantially less toxicity to human gingival fibroblasts at concentrations necessary to eradicate periodontopathogens than did clinical concentrations of chlorhexidine. These results suggest the potential utility of macromolecular NO-release scaffolds as a novel platform for the development of periodontal disease therapeutics.

Keywords: Aggregatibacter actinomycetemcomitans; Porphyromonas gingivalis; dendrimers; periodontal diseases; periodontitis; silica.

Figure 1.

Bactericidal efficacy of (A) 70 mol% MAP3 particles, (B) G1-PAMAM-PO dendrimers, and (C) proline against A. actinomycetemcomitans in Tris-PBS after 2 hr. Bactericidal efficacy of (D) 70 mol% MAP3 particles, (E) G1-PAMAM-PO dendrimers, and (F) proline against P. gingivalis in Tris-PBS after 2 hr. NO-releasing material denoted by rectangles (-■-) and non-NO-releasing controls denoted by circles (-•-). Error bars signify standard deviation of the mean viability (CFU/mL). For all measurements, n = 3 or more pooled experiments.

Figure 2.

Bactericidal efficacy of (A) 70 mol% MAP3 particles, (B) G1-PAMAM-PO dendrimers, and (C) proline against S. mutans in Tris-PBS after 2 hr. Bactericidal efficacy of (D) 70 mol% MAP3 particles, (E) G1-PAMAM-PO dendrimers, and (F) proline against S. sanguinis in Tris-PBS after 2 hr. NO-releasing material denoted by rectangles (-■-) and non-NO-releasing controls denoted by circles (-•-). Error bars signify standard deviation of the mean viability (CFU/mL). For all measurements, n = 3 or more pooled experiments.

Figure 3.

Cytotoxicity of NO-releasing materials and non-NO-releasing controls at minimum bactericidal concentration (MBC) two-hour concentrations (or maximum concentration tested). Viability measured as metabolically active fibroblasts with MTS and presented as normalized percentage relative to untreated cells. Chlorhexidine toxicity shown for clinical doses [0.12 and 0.20% (w/w)]. Of note, the numbers after the materials (e.g., 2, 4, 48, and 64) correspond to the MBC data (in mg/mL). Error bars represent standard deviation of the mean. For all values, n = 4 or more replicate measurements.