Efficacy of relacin combined with sodium hypochlorite against Enterococcus faecalis biofilms

Abstract

Objective Relacin is a synthetic molecule that targets RelA, an essential protein in a conserved bacterial stress response system. It was shown to inhibit bacterial growth. The aims of this study were to evaluate the antimicrobial effect of relacin combined with sodium hypochlorite (NaOCl) on Enterococcus faecalis biofilms and to evaluate the cytotoxicity of relacin.Material and Methods 48-h E. faecalis OG1RF biofilms were treated by various concentrations of relacin in order to determine its inhibitory concentration. Then, the 48-h biofilms were treated either with 1-min NaOCl (0.01%, 0.05%) alone, or in combination of relacin. As a means of comparison, the biofilms of ΔrelA were also treated by 1-min NaOCl (0.01%, 0.05%, 0.25%). The treatment efficacy was determined by agar plate count assays. The cytotoxicity of relacin was examined on human gingival epithelial cells Ca9-22 and murine fibroblasts NIH-3T3 by a methyl thiazolyltetrazolium (MTT) assay and a lactate dehydrogenase assay. Statistical analysis was performed by one-way or two-way analysis of variance (ANOVA) with Bonferroni’s post-hoc test and an independent Student’s t-test. A significance level of p<0.05 was used.Results Relacin inhibited the growth of OG1RF biofilms partially at 8 mM and fully at 14 mM. The relacin (14 mM) and NaOCl combined treatment resulted in significantly higher treatment efficacy than NaOCl treatment alone. At 0.05% NaOCl, the combined treatment resulted in 5.65 (±0.19) log reduction in biofilm viability. The ΔrelA biofilms were more susceptible to NaOCl treatment than the wild type biofilms at 0.25% NaOCl. Relacin at 14 mM was not toxic to host epithelial cells and fibroblasts.Conclusions The combination of relacin with a low concentration of NaOCl was effective and not cytotoxic.

Composite-derived monomers affect cell viability and cytokine expression in human leukocytes stimulated with Porphyromonas gingivalis

“…This research provides experimental evidence that UDMA induces apoptosis in lymphocytes, as described by other authors. 19 It has been suggested this resin monomer induces apoptosis through DNA lesion or mitochondrial dysfunction. 19 Heat-inactivated P. gingivalis did not induce apoptosis in lymphocytes after 5 hours of culture.…”

“… 19 It has been suggested this resin monomer induces apoptosis through DNA lesion or mitochondrial dysfunction. 19 Heat-inactivated P. gingivalis did not induce apoptosis in lymphocytes after 5 hours of culture. This finding is similar to a previous study that tested PBMC stimulated with the same bacteria.…”

Role of extracellular DNA in Enterococcus faecalis biofilm formation and its susceptibility to sodium hypochlorite

“…14 Therefore, there have been several alternative approaches proposed to improve the effectiveness of lower-concentration NaOCl solutions to avoid extensive tissue damage; however, these options have many limitations, including the requirement of inconvenient equipment. [15][16][17][18][19] Since eDNA is an essential component of E. faecalis biofilm, it can be speculated that its inhibition using a simple agent can be another strategy for effective biofilm removal. However, to our knowledge, there has been little information regarding the effect of eDNA on E. faecalis biofilm in endodontic study models.…”

The Development of a Pipeline for the Identification and Validation of Small-Molecule RelA Inhibitors for Use as Anti-Biofilm Drugs

“…The first of these inhibitors were analogs to ppGpp itself, such as Relacin and its derivatives [ 25 ]. These compounds, while mildly effective, suffer from off-target effects and low binding affinities [ 25 , 26 , 27 , 28 , 29 ].…”