The potential anti-caries activity of theaflavins (TFs): investigation of their inhibitory effect on matrix metalloproteinase-9 (MMP-9) and the underlying mechanism

This study utilized scanning electron microscopy (SEM), enzymatic kinetics, multispectral analysis, and molecular simulations to explore the effects of theaflavins (TFs) on Streptococcus mutans (S. mutans) biofilms and matrix metalloproteinase-9 (MMP-9) and the TF–MMP-9 interaction mechanism. The results demonstrated that TFs can disrupt the biofilms of S. mutans and reversibly and competitively inhibit MMP-9. TFs can spontaneously bind to MMP-9, with hydrogen bonds being the primary driving forces. Furthermore, fluorescence spectroscopy revealed that the fluorescence quenching mechanism of TFs on MMP-9 is static quenching, and this interaction alters the microenvironmental characteristics of tyrosine and tryptophan residues within MMP-9. Importantly, TFs induce a transformation of the secondary structure of MMP-9 into a more ordered and compact conformation. Interestingly, the inhibitory activity followed the order: theaflavin (TF1) < theaflavin-3-gallate (TF2A) ≈ theaflavin-3′-gallate (TF2B) < theaflavin-3,3′-digallate (TF3), suggesting that the number of galloyl groups positively correlates with the inhibitory effect. These findings indicate that TFs have great potential for application in preventing and slowing down the progression of dental caries.