Paradoxical effects of galloyl motifs in the interactions of proanthocyanidins with collagen-rich dentin

Plant-derived proanthocyanidins (PACs) mediate physicochemical modifications to the dentin extracellular matrix (ECM). The structure-activity relationships of PACs remain largely unknown, mostly due to the varied complex composition of crude extracts, as well as the challenges of purification and mechanistic assessment. To assess the role of galloylated PACs as significant contributors to high yet unstable biomodification activity to the dentin ECM, we removed the galloyl moieties (de-galloylation) via enzymatic hydrolysis from three galloyl-rich PAC-containing extracts (Camellia sinensis, Vitis vinifera, and Hamamelis virginiana). The biomechanical and biological properties of dentin were assessed upon treatment with these extracts vs. their de-galloylated counterparts. An increase in the complex modulus of the dentin matrix was found with all extracts, however, the crude extract was significantly higher when compared to the de-galloylated version. Exhibiting the highest content of galloylated PACs among the investigated plants, Camellia sinensis crude extract also exhibited the biggest relapse in mechanical properties after one-month incubation. De-galloylation did not modify the damping capacity of dentin ECM. Moreover, PAC-mediated protection against proteolytic degradation was unaffected by de-galloylation. The de-galloylation experiments confirmed that gallic acid in galloylated rich-PAC extracts drive stronger yet significantly less sustained mechanical effects in dentin ECM.