Amelogenin-inspired peptide, calcium phosphate solution, fluoride and their synergistic effect on enamel biomimetic remineralization: an in vitro pH-cycling model

BACKGROUND

Several methods were introduced for enamel biomimetic remineralization that utilize a biomimetic analogue to interact and absorb bioavailable calcium and phosphate ions and induce crystal nucleation on demineralized enamel. Amelogenin is the most predominant enamel matrix protein that is involved in enamel biomineralization. It plays a major role in developing the enamel's hierarchical microstructure. Therefore, this study was conducted to evaluate the ability of an amelogenin-inspired peptide to promote the remineralization potential of fluoride and a supersaturated calcium phosphate solution in treating artificially induced enamel carious lesions under pH-cycling regimen.

METHODS

Fifty enamel slices were prepared with a window (4*4 mm2 ) on the surface. Five samples were set as control healthy enamel and 45 samples were subjected to demineralization for 3 days. Another 5 samples were set as control demineralized enamel and 40 enamel samples were assigned into 8 experimental groups (n=5) (P/I, P/II, P/III, P/AS, NP/I, NP/II, NP/III and NP/AS) according to peptide treatment (peptide P or non-peptide NP) and remineralizing solution used (I; calcium phosphate solution, II; calcium phosphate fluoride solution, III; fluoride solution and AS; artificial saliva). Samples were then subjected to demineralization/remineralization cycles for 9 days. Samples in all experimental groups were evaluated using Raman spectroscopy for mineral content recovery percentage, microhardness and nanoindentation as healthy, demineralized enamel and after pH-cycling. Data were statistically analysed using two-way repeated measures Anova followed by Bonferroni-corrected post hoc test for pairwise multiple comparisons between groups. Statistical significance was set at p= 0.05. Additionally, XRD, FESEM and EDXS were used for crystal orientation, surface morphology and elemental analysis after pH-cycling.

RESULTS

Nanocrystals clumped in a directional manner were detected in peptide-treated groups. P/II showed the highest significant mean values in mineral content recovery (63.31%), microhardness (268.81±6.52 VHN), elastic modulus (88.74±2.71 GPa), nanohardness (3.08±0.59 GPa) and the best crystal orientation with I002/I300 (1.87±0.08).

CONCLUSION

Despite pH changes, the tested peptide was capable of remineralizing enamel with ordered crystals. Moreover, the supplementary use of calcium phosphate fluoride solution with peptide granted an enhancement in enamel mechanical properties after remineralization.

Unveiling the mechanism of an amelogenin-derived peptide in promoting enamel biomimetic remineralization

Amelogenin and its derived peptides have exhibited excellent efficacy in promoting enamel biomimetic remineralization. However, little is known about their specific action mechanisms. Herein, by combining experiments and computer simulation, the mechanism of an amelogenin-derived peptide QP5 in regulating enamel biomimetic remineralization is unveiled for the first time. In experiments, peptide QP5 was separated into (QPX)5 and C-tail domains, the interactions of peptide-minerals in nucleation solution and the regulation of peptide on enamel biomimetic remineralization were explored. QP5 exhibited an unordered conformation when mineral ions existed, and it could adsorb on minerals through its two domains, thereby inhibiting spontaneous nucleation. The remineralized enamel regulated by C-tail showed better mechanical properties and formed more biomimetic crystals than that of (QPX)5, indicating the C-tail domain of QP5 played an important role in forming enamel-like crystals. The simulation results showed that the conformation of QP5 changed greatly, mainly exhibiting β-bend, β-turn, and coil structures, and it eventually adsorbed on enamel through negatively charged residues of the C-tail domain, then captured Ca2+ from solution to promote enamel remineralization. This study improved the evaluation methods of the mechanism of biomimetic peptides, and laid a theoretical basis for the amelioration and clinical transformation of peptide QP5.

Triple Function of Amelogenin Peptide-Chitosan Hydrogel for Dentin Repair

Biomimetic strategies like peptide-guided collagen mineralization promise to enhance the effectiveness of dentin remineralization. We recently reported that rationally designed amelogenin-derived peptides P26 and P32 promoted apatite nucleation, mineralized collagen, and showed potential in enamel regrowth and dentin remineralization. To facilitate the clinical application of amelogenin-derived peptides and to uncover their effectiveness in repairing dentin, we have now implemented a chitosan (CS) hydrogel for peptide delivery and have investigated the effects of P26-CS and P32-CS hydrogels on dentin remineralization using 2 in situ experimental models that exhibited different levels of demineralization. The efficacy of the peptide-CS hydrogels in dentin repair was evaluated by characterizing the microstructure, mineral density, mineral phase, and nanomechanical properties of the remineralized samples. The new strategy of atomic force microscopy PeakForce quantitative nanomechanical mapping was used for direct visualization and nanomechanical analysis of repaired dentin lesions across the lesion depth. Results from the 2 models indicated the potential triple functions of peptide-CS hydrogels for dentin repair: building a highly organized protective mineralized layer on dentin, occluding dentinal tubules by peptide-guided in situ mineralization, and promoting biomimetic dentinal collagen remineralization. Importantly, peptides released from the CS hydrogel could diffuse into the dentinal matrix and penetrate the dentinal tubules, leading to both surface and subsurface remineralization and tubule occlusion. Given our previous findings on peptide-CS hydrogels' potential for remineralizing enamel, we see further promise for hydrogels to treat tooth defects involving multiple hard tissues, as in the case of noncarious cervical lesions.

Evaluation of the biological effects of amelogenin on human oral keratinocytes

OBJECTIVES

Amelogenins are clinically used in periodontal regeneration as main components of root surface modifying agents, even without specifically preventing the premature colonization of the healing tissue defect by means of a physical barrier membrane. The objective of this study was to investigate the effects of human amelogenin on the proliferation, migration, and morphology of Immortalized Human Oral Keratinocytes (iHOKs).

METHODS

Immortalized Human Oral Keratinocytes were expanded in Keratinocyte Growth Medium-2 (KGM-2). Full-length recombinant amelogenin protein was diluted in KGM-2 in five concentrations (10 ng/ml, 100 ng/ml, 1.000 ng/ml, 5.000 ng/ml and 10.000 ng/ml). iHOKs were cultured in medium supplemented with the amelogenin dilutions. Samples without amelogenin served as control. Cell metabolism and cell proliferation together with cell migration were evaluated at day 7, 14, 21.

RESULTS

At day 7, iHOKs treated with 10,000 ng/ml showed a significant decrease in keratinocytes´ proliferation. The metabolic activity at this timepoint was significantly lower for concentrations ≥ 1000 ng/ml. At days 14 and 21, both the addition of 5000 ng/ml and even more 10,000 ng/ml amelogenin reduced significantly the proliferation of keratinocytes. The effects on the metabolic activity for these timepoints were visible already with 100 ng/ml. Treatment of iHOKs with amelogenin of ≥ 1000 ng/ml led to inhibitory effects on cell migration already after 24 h.

CONCLUSIONS

The full-length recombinant amelogenin has a significant biological impact on iHOKs. The increasing dose dependent inhibitory effects of amelogenin shown on iHOKs might explain the disruption of the apical migration of the junctional epithelium during regenerative healing.

CLINICAL SIGNIFICANCE

Amelogenin, presents time- and dose-dependent inhibitory effects on the growth of keratinocytes, which might explain the biological rationale behind its application in periodontal regeneration.

Healing of intrabony defects using a novel human recombinant amelogenin: a preclinical study

OBJECTIVE

To histologically evaluate the effects of a novel human recombinant amelogenin (rAmelX) on periodontal wound healing/regeneration in intrabony defects.

METHOD AND MATERIALS

Intrabony defects were surgically created in the mandible of three minipigs. Twelve defects were randomly treated with either rAmelX and carrier (test group) or with the carrier only (control group). At 3 months following reconstructive surgery, the animals were euthanized, and the tissues histologically processed. Thereafter, descriptive histology, histometry, and statistical analyses were performed.

RESULTS

Postoperative clinical healing was uneventful. At the defect level, no adverse reactions (eg, suppuration, abscess formation, unusual inflammatory reaction) were observed with a good biocompatibility of the tested products. The test group yielded higher values for new cementum formation (4.81 ± 1.17 mm) compared to the control group (4.39 ± 1.71 mm) without reaching statistical significance (P = .937). Moreover, regrowth of new bone was greater in the test compared to the control group (3.51 mm and 2.97 mm, respectively, P = .309).

CONCLUSIONS

The present results provided for the first-time histologic evidence for periodontal regeneration following the use of rAmelX in intrabony defects, thus pointing to the potential of this novel recombinant amelogenin as a possible alternative to regenerative materials from animal origins.

Histological evaluation following treatment of recession-type defects with coronally advanced flap and a novel human recombinant amelogenin

OBJECTIVES

To histologically evaluate the effects of a novel human recombinant amelogenin (rAmelX) on periodontal wound healing / regeneration in recession-type defects.

MATERIALS AND METHODS

A total of 17 gingival recession-type defects were surgically created in the maxilla of three minipigs. The defects were randomly treated with a coronally advanced flap (CAF) and either rAmelX (test), or a CAF and placebo (control). At three months following reconstructive surgery, the animals were euthanized, and the healing outcomes histologically evaluated.

RESULTS

The test group yielded statistically significantly (p = 0.047) greater formation of cementum with inserting collagen fibers compared with the control group (i.e., 4.38 mm ± 0.36 mm vs. 3.48 mm ± 1.13 mm). Bone formation measured 2.15 mm ± 0.8 mm in the test group and 2.24 mm ± 1.23 mm in the control group, respectively, without a statistically significant difference (p = 0.94).

CONCLUSIONS

The present data have provided for the first-time evidence for the potential of rAmelX to promote regeneration of periodontal ligament and root cementum in recession-type defects, thus warranting further preclinical and clinical testing.

CLINICAL RELEVANCE

The present results set the basis for the potential clinical application of rAmelX in reconstructive periodontal surgery.

Biomimetic mineralisation systems for in situ enamel restoration inspired by amelogenesis

Caries and dental erosion are common oral diseases. Traditional treatments involve the mechanical removal of decay and filling but these methods are not suitable for cases involving large-scale enamel erosion, such as hypoplasia. To develop a noninvasive treatment, promoting remineralisation in the early stage of caries is of considerable clinical significance. Therefore, biomimetic mineralisation is an ideal approach for restoring enamel. Biomimetic mineralisation forms a new mineral layer that is tightly attached to the surface of the enamel. This review details the state-of-art achievements on the application of amelogenin and non-amelogenin, amorphous calcium phosphate, ions flow and other techniques in the biomimetic mineralisation of enamel. The ultimate goal of this review was to shed light on the requirements for enamel biomineralisation. Hence, herein, we summarise two strategies of biological minimisation systems for in situ enamel restoration inspired by amelogenesis that have been developed in recent years and compare their advantages and disadvantages.

Recombinant Amelogenin Protein Induces Apical Closure and Pulp Regeneration in Open-apex, Nonvital Permanent Canine Teeth

INTRODUCTION

Recombinant DNA-produced amelogenin protein was compared with calcium hydroxide in a study of immature apex closure conducted in 24 young mongrel dogs.

METHODS

Root canals of maxillary and mandibular right premolars (n = 240) were instrumented and left open for 14 days. Canals were cleansed, irrigated, and split equally for treatment with recombinant mouse amelogenin (n = 120) or calcium hydroxide (n = 120).

RESULTS

After 1, 3, and 6 months, the animals were sacrificed and the treated teeth recovered for histologic assessment and immunodetection of protein markers associated with odontogenic cells. After 1 month, amelogenin-treated canals revealed calcified tissue formed at the apical foramen and a pulp chamber containing soft connective tissue and hard tissue; amelogenin-treated canals assessed after 3- and 6-month intervals further included apical tissue functionally attached to bone by a periodontal ligament. In contrast, calcified apical tissue was poorly formed in the calcium hydroxide group, and soft connective tissue within the pulp chamber was not observed.

CONCLUSIONS

The findings from this experimental strategy suggest recombinant amelogenin protein can signal cells to enhance apex formation in nonvital immature teeth and promote soft connective tissue regeneration.

Potential of an amelogenin based peptide in promoting reminerlization of initial enamel caries

OBJECTIVE

In this study we give a preliminary study of a rationally designed small peptide, which is based on the enamel matrix protein amelogenin, to investigate its effect on remineralization of initial enamel caries lesions.

DESIGN

A novel peptide was designed and synthesized to investigate its effects on the remineralization of initial enamel carious lesions during pH cycling that simulates intra-oral conditions. Initial lesions were created in bovine enamel blocks, which were then pH-cycled for 12 days in the presence of 25μM peptide, 1g/L NaF (positive control), 50mM HEPES buffer(negative control). Before and after pH cycling, enamel blocks were analyzed by surface microhardness testing, polarized light microscopy and transverse microradiography.

RESULTS

Percentage of surface microhardness recovery (SMHR%) after pH cycling was significantly higher in peptide group than HEPES group. Lower lesion depth and less mineral mineral loss were found in peptide or NaF treatment groups after the cycling, and were significantly different to HEPES group. No significant differences were observed between the blocks treated with peptide and those treated with NaF.

CONCLUSSION

This study provides in vitro evidence that this amelogenin based peptide promotes enamel caries remineralization, offering a promising remineralizing biomaterial in initial enamel carious treatment.

Amelogenin-assisted ex vivo remineralization of human enamel: Effects of supersaturation degree and fluoride concentration

The formation of organized nanocrystals that resemble enamel is crucial for successful enamel remineralization. Calcium, phosphate and fluoride ions, and amelogenin are important ingredients for the formation of organized hydroxyapatite (HAP) crystals in vitro. However, the effects of these remineralization agents on the enamel crystal morphology have not been thoroughly studied. The objective of this study was to investigate the effects of fluoride ions, supersaturation degree and amelogenin on the crystal morphology and organization of ex vivo remineralized human enamel. Extracted third molars were sliced thin and acid-etched to provide the enamel surface for immersion in different remineralization solutions. The crystal morphology and mineral phase of the remineralized enamel surface were analyzed by field emission-scanning electron microscopy, attenuated total reflection-Fourier transformed infrared and X-ray diffraction. The concentration of fluoride and the supersaturation degree of hydroxyapatite had significant effects on the crystal morphology and crystal organization, which varied from plate-like loose crystals to rod-like densely packed nanocrystal arrays. Densely packed arrays of fluoridated hydroxyapatite nanorods were observed under the following conditions: σ(HAP)=10.2±2.0 with 1.5±0.5 mg l(-1) fluoride and 40±10 μg ml(-1) amelogenin, pH 6.8±0.4. A phase diagram summarizes the conditions that form dense or loose hydroxyapatite nanocrystal structures. This study provides the basis for the development of novel dental materials for caries management.

Controlled remineralization of enamel in the presence of amelogenin and fluoride

Reconstructing enamel-like structures on teeth have been an important topic of study in the material sciences and dentistry. The important role of amelogenin in modulating the mineralization of organized calcium phosphate crystals has been previously reported. We used amelogenin and utilized a modified biomimetic deposition method to remineralize the surface of etched enamel to form mineral layers containing organized needle-like fluoridated hydroxyapatite crystals. The effect of a recombinant amelogenins (rP172) on the microstructure of the mineral in the coating was analyzed by SEM, XRD and FT-IR. At rP172 concentrations below 33 microg/mL, no significant effect was observed. In the presence of 1 mg/L F and at a concentration of 33 microg/mL rP172, formation of fused crystals growing from the enamel surface was initiated. Amelogenin promoted the oriented bundle formation of needle-like fluoridated hydroxyapatite in a dose dependent manner. Biomimetic synthesis of the amelogenin fluoridated hydroxyapatite nano-composite is one of the primary steps towards the development and design of novel biomaterial for future application in reparative and restorative dentistry.

Amelogenin binds to both heparan sulfate and bone morphogenetic protein 2 and pharmacologically suppresses the effect of noggin

Enamel matrix derivative (EMD) is widely considered useful to promote tissue regeneration during periodontal treatment. It has been reported that the main constituent of EMD is amelogenin and that the BMP-like and TGF-beta-like activity of EMD promotes osteogenesis. However, it remains unclear whether those activities are dependent on amelogenin or another growth factor contained in EMD. We performed two-dimensional SDS-PAGE analysis of EMD, as well as Western blot analyses using anti-amelogenin, anti-BMP2/4, and anti-TGF-beta1 antibodies, and amino acid sequencing. Our results revealed that a large number of splicing forms of amelogenin, BMP2/4, and other unknown molecules were involved in EMD, though TGF-beta1 was not. In addition, we have evaluated intracellular signaling of ERK1/2 and Smad1/5/8, binding potential and alkaline phosphatase activity and have explored the potential regulatory relationship between amelogenin and BMP. Amelogenin bound to BMP2 as well as heparin/heparan sulfate. Thus, it was suggested that BMP2/4 carried over in EMD during processing promote binding activity and phosphorylate Smad1/5/8 in osteoblasts. On the other hand, amelogenin did not phosphorylate Smad1/5/8, but rather ERK1/2. Further, high-density amelogenin reduced the inhibition of alkaline phosphatase activity by noggin, though amelogenin did not have antagonistic properties against BMP. Together with the above findings, our findings suggest that the BMP2/4 contaminated during the purification process of EMD because of the avidity of amelogenin plays an important role in signaling pathway of calcification.

The enamel matrix derivative (Emdogain) enhances human tongue carcinoma cells gelatinase production, migration and metastasis formation

Enamel matrix derivative Emdogain (EMD) is widely used in periodontal treatment to regenerate lost connective tissue and to improve the attachment of the teeth. Gelatinases (MMP-2 and -9) have an essential role in the promotion and progression of oral cancer growth and metastasis formation. We studied the effects of EMD on human tongue squamous cell carcinoma (HSC-3) cells in vitro and in vivo. In vitro, EMD (100 microg/ml and 200 microg/ml) remarkably induced the MMP-2 and -9 production from HSC-3 cells analysed by zymography and enzyme-linked immunosorbent assay. EMD also slightly induced the MMP-2 and -9 production from benign human mucosal keratinocytes (HMK). Furthermore, EMD clearly induced the transmigration of HSC-3 cells but had no effect on the HMK migration in transwell assays. The in vitro wound closure of HSC-3 cells was notably accelerated by EMD, whereas it had only minor effect on the wound closure of HMKs. The migration of both cell lines was inhibited by a selective cyclic anti-gelatinolytic peptide CTT-2. EMD had no effect on HSC-3 cell proliferation or apoptosis and only a limited effect on cell attachment to various extracellular matrix components. The in vivo mice experiment revealed that EMD substantially induced HSC-3 xenograft metastasis formation. Our results suggest that the use of EMD for patients with oral mucosal carcinomas or premalignant lesions should be carefully considered, possibly avoided.