Year : 2012 | Volume
: 3 | Issue : 4 | Page : 129--132
Bio-modification approach for novel dentine caries management by Galla chinesis extract and microbial transglutaminase
Meng Deng, Xin Xu, Jiyao Li, Xuedong Zhou
Department of Endodontic and Operative Dentistry, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, PR China
No. 14, 3rd Section, Ren Min South Road, Chengdu, Sichuan Province
Introduction: Dental caries still remains one of the most prevalent diseases worldwide. Unlike enamel caries which can be restored mainly by modulating mineral balance, the dentine caries are characterized with irreversible proteolytic disintegration of organic matrices, highlighting an urgent need to seek novel management strategies. Bio-modification of dentine matrix has been proposed as a novel and alternative approach to enhancing its biochemical and biomechanical properties. The resultant chemical stability and mechanic durability are specifically desirable for prevention and restoration of dentine caries. However, conventional cross linking agents, e.g. glutaraldehyde, formaldehyde,are unsuitable for clinical use due to marked cytotoxicity or instability over time. The Hypothesis: Previous studies revealed that Galla chinesis extract (GCE) could inhibit cariogenic microbes and positively modulate enamel de/remineralization balance, and the mechanism was directed to the polyphenols-organic matrix interaction involving hydrogen, covalent, ionic bonding and hydrophobic processes. Microbial transglutaminase (mTGase) could induce crosslinks between peptide chains and improve functional properties of food proteins by catalyzing an acyl transfer reaction through ε - (γ-glutamyl) lysine (GL bonds). Given the high organic content in dentine and universal reaction nature of GCE and mTGase, we put forward a hypothesis that these two natural products may serve as novel biocompatible bio-modifiers to improve biochemical and biomechanical properties of dentine matrices. Evaluation of the Hypothesis: The validation of our hypothesis will provide profound insights updating current therapeutic strategies against dentine caries, and pioneer novel approaches for biocompatible bio-modification of dentine matrices. Specifically, GCE and mTGase can be integrated into the root canal irrigating and dentine boding procedures, where they may generate beneficial effects on preservation of integrity of dentine as well as dentine-sealer interface.
|How to cite this article:|
Deng M, Xu X, Li J, Zhou X. Bio-modification approach for novel dentine caries management by Galla chinesis extract and microbial transglutaminase.Dent Hypotheses 2012;3:129-132
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Deng M, Xu X, Li J, Zhou X. Bio-modification approach for novel dentine caries management by Galla chinesis extract and microbial transglutaminase. Dent Hypotheses [serial online] 2012 [cited 2020 Aug 15 ];3:129-132
Available from: http://www.dentalhypotheses.com/text.asp?2012/3/4/129/106835
Nowadays, dental caries still remains one of the most prevalent disease burdens worldwide, and individuals are susceptible to this disease throughout their lifetime. Dental caries is a multifactorial and chronic microbial disease resulting in the localized destruction of susceptible dental hard tissue.  Fermentation of carbohydrates drives the ecological shift of oral microbiome to be cariogenic, leading to prolonged plaque acidification. Enamel is the most highly mineralized and hardest biological tissue. The enamel caries is considered as a result of accumulative alternating episodes of de/remineralization, rather than a unidirectional demineralization process.  By modulating the mineral balance favorably to remineralization, the caries lesion can be rested or repaired through restoration of partially dissolved crystals, growth of surviving crystals and formation of new crystals.  Embodied with such capacity, fluoride has been recognized as a classical anti-caries agent.
Beneath the enamel lies the dentin, accounting for the greatest part of the dental hard tissue. The response of dentine to caries is quite distinct from that of enamel. Unlike the acellular and avascular enamel, dentine is a complex hydrated biological composite containing approximately (in weight) 70% mineral, 20% organic matrices and 10% fluids. Due to the smaller magnitude of dentinal crystallites and presence of tubules adding the permeability, the dentin shows a critical pH more than one pH-unit higher than that for enamel (critical pH≈6.7), thus more susceptible to demineralization and less apt to remineralization. , Moreover, after the mineral dissolution, the exposed dentine organic matricesare further disintegrated by proteolytic enzymes, such as bacterial-derived collagenases and host-derived matrix metalloproteinases, leading dentin deterioration to an irreversible state. , As a result, once enamel caries lesions reach the dentin-enamel junction, it can easily penetrate to deeper dentin and cause pulp irritation. To control this process of deterioration, using fluoride alone seems insufficient. Therefore, the management of dentine caries is much more challenging, highlighting an urgent need to seek novel and alternative strategies.
Bio-Modification of Dentine Matrices
The major component of dentine organic matrices is fibrillar type I collagen (90%). Type I collagen is a heterotrimeric molecule composed of two α1 chains and one α2 chain that is comprised of 3 domains: the NH2-terminal non-triple helical (N-telopeptide), the central triple helical, and the COOH terminal non-triple helical (C-telopeptide) domains.  It serves as oriented three-dimensional scaffold on which mineral crystals are orderly deposited andnon-collagenous matrices are attached. , The endogenous covalent intra- and intermolecular crosslinks, formed by post-translational modifications, can significantly stabilize type I collagen fibrils, and are the basis for mechanical properties of collagen, such as stability, fracture toughness, tensile strength, and viscoelasticity. 
Bio-modification of collagen, mostly artificially inducedby exogenous collagen crosslinks, has been proposed to help maintain, restore and improve tissue biochemical and biomechanical properties.  Specifically, these properties are desirable for prevention and restoration of dentine caries. Improved stability renders collagen compositional and structural integrity against proteolytic degradation. The stabilized collagen can further inhibit demineralization and promote remineralization. Moreover, durable mechanical properties of collagen help maintain interfacial sealing between restoratives and dentine surface, forestalling the onset of secondary caries and prolonging the life of restoration. Although hereto various crosslinking reagents, such as glutaraldehyde, formaldehyde, carbodiimide and epoxy compounds, have been used to induce exogenous crosslinks, their application in vivo has been largely limited due to cytotoxicity or instability over time. 
Galla chinensis is a natural non-toxic traditional Chinese medicine. Ancient Chinese have gained the wisdom using this medicine to treat a variety of diseases. Chemical analysis revealed that the major component inwater/ethanol extract of Galla chinensis (GCE) were monomeric and polymeric polyphenols (e.g., gallotannins, gallic acid).  A series of in vitro / in vivo studies have documented the capability of GCE to inhibit cariogenic microbe and positively modulate enamel de/remineralization balance. ,,,, In essence, the main biological function of GCE is attributed to hydrolyzable polyphenols, or gallotannins. Multiple hydrogen bonds can be formed between hydroxyl, carboxyl group in tannins and sterically bulky acidic, basic amino acid side chains in the organic matrices.  Moreover, covalent, ionic bonding and hydrophobic processes were also suggested involved in this polyphenol-matrix interaction.  This explains the fact that GCE was not able to inhibit demineralization on enamel deposed of organic matrix.  In addition, GCE was also reported to inhibit the collagenase activity in a dose-dependent manner.  Therefore, apart from modulating mineral balance, GCE may improve the tissue function of dentine by forming the GCE-dentine matrices complex, thus making the dentine more mechanically durable and less prone to be biodegraded.
Transglutaminase (TGase) is widely distributed innature and can catalyze an acyl transfer reaction between γ-carboxamide group of a peptidebound glutaminyl residue (acyl donors) and a variety of primary amines (acyl acceptors) including the amino group of lysine. In family of TGase, the microbial transglutaminase (mTGase, i.e., from Streptoverticillium mobaraense) is relatively small (28 kDa), Ca 2+ independent, and possesses a higher specific activity over a wide range of temperature and pH.  MTGase can induce covalent cross-linking of peptide chains through ε - (γ-glutamyl) lysine (G-L) bonds, bringing dramatic changes in the size, conformation, stability, solubility, emulsifying activity, and hydration properties of numerous food proteins. Previous studies have shown that the bonds formed by mTGase exhibited a high resistance to proteolytic degradation,  and porcine skin collagen crosslinked by mTGase was non-cytotoxic.  Furthermore, bovine skin collagen crosslinked by mTGase could stimulate epithelialization and neoangiogenesis without inducing any inflammatory reaction.  These advantages indicate potential superiority of mTGase over conventional crosslinkers if it could be used for polymerization of dentine collagenby formation of inter/intra-molecular G-L bonds.
Evaluation of the Hypothesis
Hereto the bio-modification potential of GCE and mTGaseon dentine is still in blank, and given the high organic content anduniversal reaction nature of GCE and mTGase, we believe that these two natural products can functionas novel biocompatible bio-modifiers to improve biochemical and biomechanical properties of dentine matrices for caries preventive/restorative purposes. The methods to testify our hypothesis are technically feasible. The fully demineralized dentine matrices can be obtained by immersing the dentine in the phosphoric acid or EDTA solution, followed by bio-modified in optimal crosslinking conditions by different treatments, i.e. GCE, mTGase as experimental groups, with double deionized water as negative control, and glutaraldehyde as positive control. Subsequently, a series of assays can be conducted for biochemical, biomechanical, morphological and biocompatibility analysis as revealed from crosslinking degree, denaturation temperature, resistance against bacterial collagenase, ultimate tensile strength and cytotoxicity to dental pulp cells. The validation of our hypothesis will provide profound insights updating current therapeutic strategies against dentine caries, and pioneer novel approaches for biocompatible bio-modification of dentine matrices. Specifically, GCE and mTGase can be integrated into the root canal irrigating and dentine boding procedures, and they may generate beneficial effects on preservation of integrity of dentine as well as dentine-sealer interface.
This work was supported by the Scientific Research Foundation for Young Investigators, Sichuan University, China (2011scu11999-2), the National Basic Research Program of China ("973 Pilot Research Program", 2011 CB512108) and the Research Fund from Science and Technology Department of Sichuan Province (No. 2009FZ0065).
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