Influence of Nonenzymatic Glycation in Dentinal Collagen on Dental Caries

Glycation promotes pulp calcification in Type 2 diabetes rat model

OBJECTIVES

Intrapulpal calcifications can occur in the dental pulp of patients with diabetes. We focused on the association between ectopic calcifications in the dental pulp and advanced glycation end products (AGEs) in Spontaneously Diabetic Torii (SDT)-fatty rats, an obese type 2 diabetic rat model, to determine the mechanism of calcification with pulp stone in the dental pulp.

MATERIALS AND METHODS

Pathologic calcification in the dental pulp of SDT-fatty rats was observed using electron microscopy and immunohistochemical analysis. Moreover, mechanical analysis of periapical region of molar tooth against occlusal force was performed.

RESULTS

In SDT-fatty rats, pathogenic pulpal calcifications occurred during blood glucose elevation after 6 weeks, and granular calcification was observed in the dental pulp after 11 weeks. Pentosidine, a major AGE, and the receptor for AGEs were strongly expressed in the dental pulp of SDT-fatty rats. S100A8, TNF-α, and IL-6 also showed positive response in the dental pulp of the SDT-fatty rat, which indicated pulpal inflammation. Blood flow disorder and hypoxic dental pulp cells were also observed. In silico simulation, strain from occlusal force concentrates on the root apex.

CONCLUSIONS

Glycation makes blood vessels fragile, and occlusal forces damage the vessels mechanically. These are factors for intrapulpal calcification of diabetes.

Comparison of collagen features of distinct types of caries-affected dentin

OBJECTIVES

To compare the biodegradability, mechanical behavior, and physicochemical features of the collagen-rich extracellular matrix (ECM) of artificial caries-affected dentin (ACAD), natural caries-affected dentin (NCAD) and sound dentin (SD).

METHODS

Dentin specimens from human molars were prepared and assigned into groups according to the type of dentin: ACAD, NCAD, or SD. ACAD was produced by incubation of demineralized SD with Streptococcus mutans in a chemically defined medium (CDM) with 1% sucrose for 7 days at 37 °C under anaerobic conditions. Specimens were assessed to determine collagen birefringence, biodegradability, mechanical behavior, and chemical composition. Data were individually processed and analyzed by ANOVA and post-hoc tests (α = 0.05).

RESULTS

CDM-based biofilm challenge reduced loss, storage, and complex moduli in ACAD (p < 0.001), while the damping capacity remained unaffected (p = 0.066). Higher red and lower green birefringence were found in ACAD and NCAD when compared with SD (p < 0.001). Differently to ACAD, SD and NCAD presented higher biodegradability to exogenous proteases (p = 0.02). Chemical analysis of the integrated areas of characteristic bands that assess mineral quality (carbonate/phosphate and crystallinity index), mineral to matrix (phosphate/amide I) and post-translational modifications (amide III/CH₂, pentosidine/CH₂, and pentosidine/amide III) (p<0.05) showed that NCAD was significantly different from SD while ACAD exhibited intermediate values.

CONCLUSIONS

CDM-based biofilm challenge produced a dentin ECM with decreased mechanical properties and increased collagen maturity. The compositional and structural conformation of the ACAD suggested that CDM-based biofilm challenge showed potential to produce artificial lesions by revealing a transitional condition towards mimicking critical features of NCAD.

CLINICAL SIGNIFICANCE

This study highlights the importance of developing a tissue that mimics the features of natural caries-affected dentin ECM for in vitro studies. Our findings suggested the potential of a modified biofilm challenge protocol to produce and simulate a relevant substrate, such as caries-affected dentin.

Nanomechanical and Nonlinear Optical Properties of Glycated Dental Collagen

Nonenzymatic glycation is a multistep, slow reaction between reducing sugars and free amino groups of long-lived proteins, which affects the structural and mechanical properties of collagen-rich tissues via accumulation of advanced glycation end products (AGEs). Dental collagen is exposed to glycation as part of the natural aging process. However, in case of chronically high blood glucose, the process can be accelerated, resulting in premature stiffening of dentin, leading to tooth fragility. The molecular mechanisms whereby collagen glycation evokes the loss of mechanical stability in teeth are currently unknown. In this study, we used 2-photon and atomic force microscopies to correlate structural and mechanical changes in dental collagen induced by in vitro glycation. Young tooth samples were demineralized and cut longitudinally into 30-µm sections, then artificially glycated in 0.5 M ribose solution for 10 wk. Two-photon microscopy analysis showed that both the autofluorescence and second harmonic-generated (SHG) signal intensities of glycated samples were significantly greater than those of the controls. Regarding the structural alteration of individual collagen fibers, a remarkable increase could be measured in fiber length of ribose-treated sections. Furthermore, nanoindentation of intertubular dentin regions revealed significantly higher stiffness in the ribose-treated samples, which points at a significant accumulation of AGEs. Thus, collagen glycation occurring during sustained exposure to reducing sugars leads to profound structural and mechanical changes in dentin. Besides the numerous oral complications associated with type 2 diabetes, the premature structural and mechanical deterioration of dentin may also play an important role in dental pathology.

Effects of advanced glycation end products on dental pulp calcification

OBJECTIVE

The main aim of this study was to elucidate the effects of advanced glycation end products (AGEs) on the calcification of cultured rat dental pulp cells (RDPCs) and to investigate the crystallisation ability of glycated collagen.

MATERIALS AND METHODS

AGEs were prepared via non-enzymatic glycation of a dish coated with type I collagen using dl-glyceraldehyde. To investigate the effects of AGEs on RDPCs, we performed WST-1 and lactate dehydrogenase assays; alkaline phosphatase, Alizarin Red S and immunohistochemical staining; and real-time quantitative reverse transcription PCR. In addition, we performed crystallisation experiments on glycated collagen. All microstructures were analysed using scanning electron microscopy/energy-dispersive X-ray spectroscopy and transmission electron microscopy/diffraction pattern analysis.

RESULTS

AGEs did not affect the proliferation or differentiation of RDPCs, but enhanced the calcification rate and cytotoxicity. No major calcification-related genes or proteins were involved in these calcifications, and glycated collagen was found to exhibit a negative polarity and form calcium phosphate crystals. Cytotoxicity due to drastic changes in the concentration of pericellular ions led to dystrophic calcification, assumed to represent an aspect of diabetic pulp calcifications.

CONCLUSION

Glycated collagen-containing AGEs provide a nurturing environment for crystallisation and have a significant effect on the early calcification of RDPCs.

A macroscopic and histological analysis of radiographically well-defined deep and extremely deep carious lesions: carious lesion characteristics as indicators of the level of bacterial penetration and pulp response

AIM

To investigate the relationship between radiographically and macroscopically well-defined carious lesions and the dentine-pulp complex with regard to: (i) level of bacterial penetration; (ii) inflammatory status including the presence of hyperplastic pulp stroma; and (iii) formation of hard and/or ectopic connective tissue.

METHODOLOGY

The material comprised 68 untreated cavitated permanent teeth divided into well-defined radiographic categories based on the lesion penetration depth: (i) deep lesions ( ≥3/4 of the dentine thickness with a radio-dense zone separating the lesion from the pulp) and (ii) extremely deep lesions (the carious lesion penetrated the entire thickness of the dentine, without a radio-dense zone). After extraction, the teeth were processed for histology. The material was scored with regard to coronal breakdown, macroscopic variables describing caries activity and histological variables describing the dentine-pulp complex (bacteria, inflammatory infiltrate, partial pulp necrosis, hyperplastic changes and hard tissue/ectopic presence of connective tissue). Interrater agreement was assessed using Cohen's kappa. Associations between variables were assessed using Pearson's chi-squared or Fisher's exact test. The effect size was reported by odds ratio (OR) and associated 95% confidence interval (CI). Level of significance was set to 5%.

RESULTS

There were significant associations between a closed environment (1-2 surfaces involved) and the presence of biofilm, retrograde demineralization and light-coloured demineralized dentine. Whereas radiographically defined deep lesions tended to have bacteria only in the primary dentine (P < 0.001, OR = 20.55, 95% CI [4.44, 107.89]), extremely deep carious lesions tended to have bacteria in contact with the pulpal tissue (P = 0.007, OR = 6.84, 95% CI [2.00, 62.83]), presence of an inflammatory infiltrate (Fisher's exact; P < 0.001) and partial pulp necrosis. Hyperplastic pulps were seen only in extremely deep lesions.

CONCLUSIONS

Unlike deep lesions, extremely deep carious lesions were often associated with severe pulp inflammation and infection. A radiographic threshold between deep and extremely deep lesions is suggested as indicator of the bacterial penetration level and the severity of the pulpal response prior to intervention.

On the bulk biomechanical behavior of densely cross-linked dentin matrix: The role of induced-glycation, regional dentin sites and chemical inhibitor

Collagen glycation takes place under physiological conditions during chronological aging, leading to the formation of advanced glycation end-products (AGEs). AGEs accumulation induces non-enzymatic collagen cross-links increasing tissue stiffness and impairing function. Here, we focused on determining the cumulative effect of induced glycation on the mechanical behavior of highly collagen cross-linked dentin matrices and assess the topical inhibition potential of aminoguanidine. Bulk mechanical characterization suggests that early glycation cross-links significantly increase the tensile strength and stiffness of the dentin matrix and promote a brittle failure response. Histologically, glycation yielded a more mature type I collagen in a densely packed collagen matrix. The time-dependent effect of glycation indicates cumulative damage of dentin matrices that is partially inhibited by aminoguanidine. The regional dentin sites were differently affected by induced-glycation, revealing the crown dentin to be mechanically more affected by the glycation protocol. These findings in human dentin set the foundation for the proposed in vitro ribose-induced glycation model, which produces an early matrix stiffening mechanism by reducing tissue viscoelasticity and can be partially inhibited by topical aminoguanidine.

Preparation of low-molecular-weight, collagen hydrolysates (peptides): Current progress, challenges, and future perspectives

Collagen hydrolysates (peptides) derived from food processing byproducts have been used to produce commercially valuable food ingredients due to their potential to trigger certain desirable physiological responses in the body. Low-molecular-weight (LMW) collagen hydrolysates are generally thought to exert better bioactivities than their larger counterparts. However, the preparation of LMW collagen hydrolysates is often impeded by their special structure, cross-linking, and hydroxyproline. This review briefly introduces the motivation of the food industry to prepare LMW collagen hydrolysate from food processing byproducts. We further summarize recent progress on the preparation of LMW collagen hydrolysates and methods to determine the molecular weight. We then discuss the challenges and then provide perspectives on future directions in preparing LMW collagen hydrolysates.

UVA-activated riboflavin promotes collagen crosslinking to prevent root caries

Root caries is an increasingly problem in aging societies with severe implications for the general health and wellbeing of large numbers of people. Strengthening type-I collagen, a major organic component of human dentin, has proved effective in preventing root caries. This study sought to determine whether exposure to riboflavin followed by UVA irradiation (RF/UVA) could promote additional collagen crosslinking, and thus improve the acid and enzymatic resistance of human dentin under simulated oral environments. If so, it could offer potential for treatment of the intractable problem of root caries. The greatest flexural strengths were found in dentin exposed to a 0.1% riboflavin solution for 1 minute followed by 1,600 mW/cm² UVA irradiation for 10 minutes. Mineral loss and lesion depth were significantly lower in the RF/UVA group than in the control group. The microstructures of dentinal tubules and collagen networks after RF/UVA treatment retained their original forms after acidic and enzymatic degradation. In conclusion, RF/UVA treatment may be a new method for preventing root caries with promising prospects for clinical application.

Novel Biomedical Applications of Crosslinked Collagen

Collagen is one of the most useful biopolymers because of its low immunogenicity and biocompatibility. The biomedical potential of natural collagen is limited by its poor mechanical strength, thermal stability, and enzyme resistance, but exogenous chemical, physical, or biological crosslinks have been used to modify the molecular structure of collagen to minimize degradation and enhance mechanical stability. Although crosslinked collagen-based materials have been widely used in biomedicine, there is no standard crosslinking protocol that can achieve a perfect balance between stability and functional remodeling of collagen. Understanding the role of crosslinking agents in the modification of collagen performance and their potential biomedical applications are crucial for developing novel collagen-based biopolymers for therapeutic gain.