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 NaB3H4-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 NaB3H4.
Highlights
Fibrillar type I collagen is the major organic component in dentin matrix and functions as a stable template to spatially regulate mineral deposition and growth [1,2,3]
The demineralized dentin collagen treated with GE exhibited distinct features
Dentin collagen in the control group presented a white color while a concentration- and time-dependent dark blue pigmentation was observed in the GE-treated groups (Figure 1)
Summary
Fibrillar type I collagen is the major organic component in dentin matrix and functions as a stable template to spatially regulate mineral deposition and growth [1,2,3]. Covalent intermolecular cross-linking is the final posttranslational modification and is crucial for the stability, tensile strength, and viscoelasticity of collagen matrix [4,5,6,7,8]. Lysyl oxidase (LOX-) mediated collagen cross-linking has been extensively studied [5, 9,10,11,12]. The chemical structure and the quantity of these cross-links are primarily determined by the extent of hydroxylation of specific lysine (Lys) residues in the collagen molecule and the extent of oxidative deamination of the Lys and hydroxylysine (Hyl) residues in the telopeptide domains of the molecule. The glycosylation pattern of specific helical Hyl residues that are involved in crosslinking may modulate the maturation of collagen cross-links [13]. The cross-linking pattern can be determined by the maturation/turnover rate of tissues [14,15,16,17,18], the details of molecular packing structure [18,19,20], and the physical force exerted on the tissue [21]
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