Rutin-gallium complex mediated antimicrobial photodynamic therapy: An in vitro studies against Streptococcus mutans biofilms

Background: Discoloration of teeth following antimicrobial photodynamic therapy (aPDT) is a serious concern. Common photosensitizers are colored, and access to a photosensitizer that does not leave color on the teeth or is the same color as the enamel and dentin is highly demanded. The physicochemical characterization, anti -virulence, and antimicrobial effects of a novel rutin-gallium (III) (Rt-Ga) complex as novel photosensitizer are presented herein.Materials and Methods: Photophysical properties and cytotoxicity of the Rt-Ga complex were evaluated in com-parison with the parental rutin. Intracellular reactive oxygen species (ROS) generation following Rt-Ga complex -mediated aPDT was measured using the fluorescent 2 ',7 '-dichlorofluorescein diacetate (H2DCF-DA) method. The anti-biofilm effects of Rt-Ga complex-mediated aPDT on Streptococcus mutans were assessed using a colorimetric assay. The virulence-associated gtfB gene expression was assessed following Rt-Ga complex-mediated aPDT by quantitative real-time PCR.Results: The photophysical properties of the Rt-Ga complex revealed a significant blue-shift in absorption (60 nm shift) and increased extinction coefficient (4100 M-1 cm-1; at lambda max = 450 nm). Average (+/- SEM) DCF fluorescence intensities in an arbitrary unit (A.U.) were 7.1 +/- 0.9, 4.1 +/- 0.5, and 1.7 +/- 0.3 for 10.0 mu M of Rt-Ga complex-mediated aPDT, 7.5 mu M of Rt-Ga complex-mediated aPDT, and 10.0 mu M of Rt-Ga complex alone, respectively. The corresponding DCF fluorescence intensities were 710% (P = 0.001), 410% (P = 0.001), and 170% (P = 0.02) of the untreated S. mutans as the control group (1.0 +/- 0.1 A.U.), respectively. The novel Rt-Ga complex-mediated aPDT exhibited no toxicity against primary human gingival fibroblast cells, a dose dependent decrease in S. mutans biofilm cell survival and virulence were observed (91.4% and 11.7-fold, respectively).Conclusion: The Rt-Ga complex-mediated anti-virulence and antimicrobial photodynamic effects were superior to the one caused by rutin alone making the Rt-Ga complex a more promising photosensitizer than the parent material.