Anti-virulence effect of photoactivated nano-quercetin by diode laser on Aggregatibacter actinomycetemcomitans

Photodynamic therapy (PDT) is an innovative, non-invasive, and selective treatment approach that has gained attention as an adjunctive treatment in periodontitis. Aggregatibacter actinomycetemcomitans is an opportunistic periodontopathogen known for its ability to form biofilms. The objective of this in vitro study was to determine the anti-virulence effect of nano-quercetin (N-QT)-mediated PDT on the expression of a gene associated with biofilm formation of A. actinomycetemcomitans. After synthesis and characterization of N-QT by transmission electron microscopes (TEM), dynamic light scattering (DLS), zeta potential analysis, and fourier transform infrared spectroscopy (FTIR) analysis, the effects of different concentrations of N-QT and energy densities of diode laser alone on cell viability of A. actinomycetemcomitans were evaluated. A. actinomycetemcomitans was then treated by sub-lethal doses of diode laser emitting light in the presence of sub-lethal doses of N-QT. Ultimately, the sub-lethal dose of PDT was used to investigate the metabolic activity of A. actinomycetemcomitans, the generation of reactive oxygen species (ROS), and changes in rcpA, qseB, and qseC genes expression using the quantitative real-time polymerase chain reaction (qRT-PCR) method. According to the results, TEM, DLS, zeta potential, and FTIR confirmed the synthesis of N-QT. PDT with concentrations of 16 to 512 µg/mL of N-QT alone and irradiation for 6 min with an energy density of 154.8 J/cm² alone caused a significant decrease in bacterial count (P < 0.05). PDT with 8 µg/mL N-QT and 5-min irradiation achieved the highest metabolic activity reduction (42.9%), while 2 µg/mL N-QT and 4-min irradiation yielded the lowest reduction (12.3%). Using 8 µg/mL of N-QT with light exposure for 4 and 5 min at energy densities of 103.9 and 129 J/cm² led to ROS levels that were 2.67- and 2.83-fold higher than those in the control cells, respectively (P < 0.05). Additionally, the sub-lethal dose of PDT with 5 min of irradiation in the presence of 2 µg/mL of N-QT resulted in a 2.62-, 2.85-, and 3.21-fold decrease in the expression levels of the rcpA, qseB, and qseC genes, respectively (P < 0.05). PDT utilizing N-QT and diode laser shows promise in suppressing cellular survival and emerges as a viable strategy for targeting A. actinomycetemcomitans virulence.