Resveratrol-loaded human dental pulp stem cell-derived exosomes enhance the efficacy of blue LED-mediated antimicrobial photodynamic therapy against mature cariogenic biofilms

Antimicrobial photodynamic therapy (aPDT) is a promising adjunctive approach for biofilm-associated oral diseases, though the poor stability and bioavailability of natural photosensitizers remain limiting factors. This study evaluated the anti-biofilm efficacy of resveratrol-loaded human dental pulp stem cell-derived exosomes (Res@hDPSC-Exos) activated by blue LED irradiation against mature cariogenic biofilms. hDPSC-Exos were isolated, characterized, and loaded with resveratrol; physicochemical properties, encapsulation efficiency, and exosomal integrity were assessed by TEM, DLS, and CD63 expression. Mature Streptococcus mutans and Lactobacillus acidophilus biofilms were established on human enamel specimens. The minimum biofilm reduction concentration (MBRC) of Res@hDPSC-Exos and minimum biofilm reduction dose (MBRD) of blue LED were determined, and biofilms were treated according to six groups: untreated control, free resveratrol, empty hDPSC-Exos, blue LED alone, and Res@hDPSC-Exos-mediated aPDT at 1/2× and 1/4×MBRC. Biofilm biomass, metabolic activity, and gtfB/slpA virulence gene expression were assessed by crystal violet staining, XTT assay, and qRT-PCR, respectively. Resveratrol was successfully encapsulated into hDPSC-Exos (encapsulation efficiency ≈ 63%) without compromising vesicle morphology or membrane integrity. The MBRC of Res@hDPSC-Exos was 250 µg/mL for S. mutans and 125 µg/mL for L. acidophilus, and the MBRD of blue LED was 300 s for both species. Free resveratrol, empty hDPSC-Exos, and blue LED alone produced only modest, non-significant effects (≈ 5-15%, P > 0.05). In contrast, Res@hDPSC-Exos-mediated aPDT at 1/2×MBRC with sub-MBRD irradiation (240 s) significantly reduced biofilm biomass (84.7% and 75.2%) and metabolic activity (88.9% and 85.0%) in S. mutans and L. acidophilus, respectively (P < 0.001), and downregulated gtfB and slpA expression to 0.15-fold and 0.19-fold of controls (P < 0.001). Res@hDPSC-Exos-mediated aPDT effectively suppressed biofilm growth, metabolic activity, and virulence gene expression in mature cariogenic biofilms under conservative irradiation conditions. Given the minimal activity of the individual components relative to the combined treatment, exosome-assisted delivery may contribute to enhancing the photodynamic performance of resveratrol; however, as this study did not directly compare free resveratrol- and exosome-mediated aPDT under identical conditions, this interpretation should be regarded as preliminary. Further in vivo, clinical, and comparative studies are warranted to confirm its translational potential.