Characterization of genipin-modified dentin collagen

Abstract

Application of biomodification techniques to dentin can improve its biochemical and biomechanical properties. Several collagen cross-linking agents have been reported to strengthen the mechanical properties of dentin. However, the characteristics of collagen that has undergone agent-induced biomodification are not well understood. The objective of this study was to analyze the effects of a natural cross-linking agent, genipin (GE), on dentin discoloration, collagen stability, and changes in amino acid composition and lysyl oxidase mediated natural collagen cross-links. Dentin collagen obtained from extracted bovine teeth was treated with three different concentrations of GE (0.01%, 0.1%, and 0.5%) for several treatment times (0-24 h). Changes in biochemical properties of NaB(3)H4-reduced collagen were characterized by amino acid and cross-link analyses. The treatment of dentin collagen with GE resulted in a concentration- and time-dependent pigmentation and stability against bacterial collagenase. The lysyl oxidase-mediated trivalent mature cross-link, pyridinoline, showed no difference among all groups while the major divalent immature cross-link, dehydro-dihydroxylysinonorleucine/its ketoamine in collagen treated with 0.5% GE for 24 h, significantly decreased compared to control (P < 0.05). The newly formed GE-induced cross-links most likely involve lysine and hydroxylysine residues of collagen in a concentration-dependent manner. Some of these cross-links appear to be reducible and stabilized with NaB(3)H4.

Figure 1

Discoloration of GE-modified dentin collagen. Photographs of the representative discoloration of dentin collagen treated with PBS (control) and three different concentrations (0.01%, 0.1%, and 0.5%) of genipin (GE) for six treatment durations (30 min, 1 h, 4 h, 8 h, 12 h, and 24 h).

Figure 2

Collagen stability of GE-modified dentin collagen. 2 mg aliquots of demineralized dentin treated with PBS (control) and three concentrations of genipin (GE) (0.01%, 0.1%, and 0.5%) for six treatment durations (30 min, 1 h, 4 h, 8 h, 12 h, and 24 h) were subjected to collagenase digestion and hydroxyproline (Hyp) analysis. The mean amounts of undigested collagen with bacterial collagenase are shown as Hyp content (nM) in the insoluble residues. (n = 3). *P < 0.001, **P < 0.0001 which are different from the value of control. ^ƚ P < 0.0001 which is different from the value of 0.1% GE. ^a P < 0.001, ^b P < 0.0001 which are different from the value of 0.5% GE.

Figure 3

Representative chromatographs of (a) reducible and (b) nonreducible collagen cross-links in 24 h treatment duration of PBS (control) and three concentrations of genipin (GE) (0.01%, 0.1%, and 0.5%) groups.