Chitosan hydrogel containing amelogenin-derived peptide: Inhibition of cariogenic bacteria and promotion of remineralization of initial caries lesions

Objective: Nowadays, caries prevention focuses on controlling pathogenic bacteria, inhibiting demineralization and promoting re-mineralization. The aim of this study is to design a more clinically powerful anti-caries treatment by combining amelogenin-derived peptide QP5 with antibacterial chitosan in a hydrogel (CS-QP5 hydrogel), and characterize its effects on inhibition of cariogenic bacteria and promotion of remineralization of initial caries lesions. Design: CS-QP5 interactions at different pH and chitosan concentrations were studied using UV-vis spectroscopy, fluorescence spectroscopy and circular dichroism. Antibacterial activity was measured using broth microdilution and biofilm assays. Remineralizing activity was measured using tests of surface micro-hardness (SMH), polarized light microscopy(PLM) and transverse microradiography(TMR) in a pH cycling model that simulates intra-oral pH conditions. Results: The results of UV vis spectroscopy, fluorescence spectroscopy and circular dichroism analyses suggest that the micro-environment of QP5 changes upon addition of chitosan and the interaction between QP5 and chitosan is reversible and dependent on pH. CS-QP5 hydrogel showed good antibacterial potency towards Streptococcus mutans with MIC/MBC of 5 mg/mL, reducing adhesion and biofilm formation up to 95.43% and nearly 100% respectively. According to the results of remineralizing studies, CS-QP5 hydrogel demonstrated 50.06% surface micro-hardness recovery, shallower lesion depth, significantly less mineral loss and more mineral content at different depth in the lesion body after pH cycling. Conclusions: The hydrogel showed promise as a dual-action caries control agent in vitro, whether it could present good effects in vivo still needs to be determined, which requires further study. Nonetheless, the new design of bioactive hydrogel with antibacterial and remineralizing properties has the potential to substantially benefit oral health.