Potential induction of bone regeneration by nacre: an in vitro study

The Use of Shells of Marine Molluscs in Spanish Ethnomedicine: A Historical Approach and Present and Future Perspectives

Since ancient times, the shells of marine molluscs have been used as a therapeutic and/or prophylactic resource. In Spain, they were part of practical guides for doctors or pharmacists until the 19th century. In general, seashells were prepared by dissolving in vinegar and were part of plasters or powders used as toothpaste, or to treat dyspepsia, heartburn and leprosy. Thus, the nacre or mother-of-pearl of various molluscs was regularly used in the Royal Colleges of Surgery and in hospitals during the times of the Cortes of Cadiz, as a medicine in galenic preparations based on powders. In contemporary Spanish ethnomedicine, seashells, with a high symbolic value, have been used as an amulet to prevent cracks in the breasts and promote their development during lactation, to avoid teething pain in young children, to eliminate stains on the face or to cure erysipelas. But, as in other countries, products derived from seashells have also been empirically applied. The two resources used traditionally have been the cuttlebone, the internal shell of cuttlefish and the nacre obtained from the external shells of some species. Cuttlebone, dried and pulverised, has been applied externally to cure corneal leukoma and in dental hygiene. In the case of nacre, a distinction must be made between chemical and physical remedies. Certain seashells, macerated in lemon juice, were used in coastal areas to remove spots on the face during postpartum. However, the most common practice in Spain mainland was to dissolve mother-of-pearl buttons in lemon juice (or vinegar). The substance thus obtained has been used to treat different dermatological conditions of the face (chloasma, acne), as well as to eliminate freckles. For the extraction of foreign bodies in the eyes, a very widespread traditional remedy has been to introduce small mother-of-pearl buttons under the lid. These popular remedies and practices are compared with those collected in classic works of medicine throughout history, and data on the pharmacological activity and pharmaceutical applications of the products used are provided. The use of cuttlebone powders is supported by different works on anti-inflammatory, immune-modulatory and/or wound healing properties. Nacre powder has been used in traditional medicines to treat palpitations, convulsions or epilepsy. As sedation and a tranquilisation agent, nacre is an interesting source for further drug development. Likewise, nacre is a biomaterial for orthopaedic and other tissue bioengineering applications. This article is a historical, cultural and anthropological view that can open new epistemological paths in marine-derived product research.

Nacre Extract from Pearl Oyster Shell Prevents D-Galactose-Induced Brain and Skin Aging

Pearl oyster shells comprise two layers, a prismatic and nacreous layer, of calcium carbonate. The nacreous layer has been used in Chinese medicine since ancient times. In this study, we investigated the effects of the extract from the nacreous layer of pearl oysters (nacre extract) on D-galactose-induced brain and skin aging. Treatment with nacre extract led to the recovery of D-galactose-induced memory impairment, as examined using the Barnes maze, novel object recognition, and Y-maze tests. A histological study showed that nacre extract suppressed D-galactose-induced neuronal cell death and the expression of B cell lymphoma 2 (Bcl-2)-associated X protein (Bax), which causes apoptosis in the hippocampus. In addition, the expression levels of brain-derived neurotrophic factor, which counteracts age-related brain dysfunction, and nicotinamide adenine dinucleotide-dependent deacetylase (sirtuin 1), which delays aging and extends lifespan, increased after nacre extract treatment. Moreover, the nacre extract showed anti-aging effects against D-galactose-induced skin aging; it suppressed D-galactose-induced wrinkle formation, decreased skin moisture, decreased epidermal thickness, and destroyed collagen arrangement associated with aging. Furthermore, the nacre extract suppressed oxidative stress associated with aging in the brain and skin by upregulating the expression of catalase and superoxide dismutase. The expression level of the cellular senescence marker p16, which is induced by oxidative stress, was elevated in the hippocampus and skin epidermal layer of D-galactose-treated mice, and it was suppressed by the administration of nacre extract. These results show that the nacre extract can suppress D-galactose-induced aging by enhancing anti-oxidant activity and suppressing p16 expression. Thus, the nacre extract may be an effective anti-aging agent.

The Application of Pearls in Traditional Medicine of China and Their Chemical Constituents, Pharmacology, Toxicology, and Clinical Research

Although pearls are well known by most people, their medicinal value has not been popularized. This article collates the medicinal history of pearls over 2,000 years in China, including the application of pearls in the traditional medicine of China and their various preparations, as well as the progress of their chemical constituents, pharmacology, toxicology, and clinical research. Pearls from three different sources are used as medical materiel by 9 nationalities and 251 prescription preparations in China. In addition, pearls contain various inorganic constituents, such as calcium carbonate, trace elements, and water, and organic constituents, such as amino acids. In terms of pharmacology, pearls have many effects such as calming, improving cognitive ability, being anti-epileptic, promoting bone growth and regeneration, promoting the proliferation and migration of human microvascular endothelial cells, protecting the heart, anti-hemolysis, and anti-oxidation. In terms of toxicology, pearls are safe to take for a long time without exerting obvious adverse reactions. In terms of clinical application, pearls have been used to treat many diseases and conditions, such as convulsions, epilepsy, palpitations, eye diseases, ulcer diseases, skin diseases, or skin lesions. This article provides a reference for the application and research of pearls in the future.

Induction of Osseointegration by Nacre in Pigs

Nacre is a biomaterial that has shown osteoinductive and osteoconductive properties in vitro and in vivo. These properties make nacre a material of interest for inducing bone regeneration. However, information is very limited regarding the introduction of nacre to dental implant surgery for promoting osteogenesis. This study investigated the potential of nacre powder for peri-implant bone regeneration in a porcine model. Ninety-six dental implants were placed into the tibia of twelve male domestic pigs. The dental implants were coated with nacre powder from the giant oyster before implantation. Implantations without nacre powder were used as control groups. Euthanization took place at 2, 4 and 6 weeks after implantation, after which we measured bone-to-implant contact (BIC) and bone volume density (BVD) of the implanted bone samples using micro-computed tomography (micro-CT), and examined the histology of the surrounding bone using histological sections stained with Stevenel’s blue and Alizarin red S. The micro-CT analyses showed that the BIC of dental implantations with nacre powder were significantly higher than those without nacre powder, by 7.60%. BVD of implantations with nacre powder were significantly higher than those without nacre powder, by 12.48% to 13.66% in cortical bone, and by 3.37% to 6.11% in spongy bone. Histological study revealed more peri-implant bone regeneration toward the surface of the dental implants after implantation with nacre powder. This was consistent with the micro-CT results. This study demonstrates the feasibility of using nacre to promote peri-implant bone regeneration in dental implantation.

Pearl Powder-An Emerging Material for Biomedical Applications: A Review

Pearl powder is a well-known traditional Chinese medicine for a variety of indications from beauty care to healthcare. While used for over a thousand years, there has yet to be an in-depth understanding and review in this area. The use of pearl powder is particularly growing in the biomedical area with various benefits reported due to the active ingredients within the pearl matrix itself. In this review, we focus on the emerging biomedical applications of pearl powder, touching on applications of pearl powder in wound healing, bone repairing, treatment of skin conditions, and other health indications.

Extraction, Purification, Bioactivities and Application of Matrix Proteins From Pearl Powder and Nacre Powder: A Review

Natural pearls are formed when sand or parasites (irritants) accidentally enter into the oyster body and form pearls under the cover of the nacre layer. Pearl powder is a powdery substance by grinding pearls into small grains, however, the nacre powder is the inner layer of outer corner layer and middle prism layer. Pearl medicine in China has a history of more than 2,000 years, pearl has the effects of calming the mind, clearing the eyes, detoxifying the muscle and so on. In this paper, the researches on the extraction of pearl powder and nacre powder, the isolation and purification of matrix protein and the various biological activities (osteogenic activity, antioxidant, anti-inflammatory, anti-apoptotic, promoting the migration of fibroblasts, and so on) are reviewed in detail. To provide readers with a faster understanding, the method of extraction and purification and the application of nacre powder and pearl powder are clearly presented in the form of figures and tables. In line with the concept of waste or by-product, there are more reports of nacre extract than pearl extract, due to the expensive and limited in origin of pearls. Mainly on the direct use of nacre powder and pearl powder or on the use of extracts (mainly water soluble proteins) through experiments in vivo or in vitro, and shows whether it is effective through the results of various indexes. There is no further study on substances other than extracts, and the structural analysis of extracts needs further exploration.

Effects of the Sintering Process on Nacre-Derived Hydroxyapatite Scaffolds for Bone Engineering

A hydroxyapatite scaffold is a suitable biomaterial for bone tissue engineering due to its chemical component which mimics native bone. Electronic states which present on the surface of hydroxyapatite have the potential to be used to promote the adsorption or transduction of biomolecules such as protein or DNA. This study aimed to compare the morphology and bioactivity of sinter and nonsinter marine-based hydroxyapatite scaffolds. Field emission scanning electron microscopy (FESEM) and micro-computed tomography (microCT) were used to characterize the morphology of both scaffolds. Scaffolds were co-cultured with 5 × 104/cm2 of MC3T3-E1 preosteoblast cells for 7, 14, and 21 days. FESEM was used to observe the cell morphology, and MTT and alkaline phosphatase (ALP) assays were conducted to determine the cell viability and differentiation capacity of cells on both scaffolds. Real-time polymerase chain reaction (rtPCR) was used to identify the expression of osteoblast markers. The sinter scaffold had a porous microstructure with the presence of interconnected pores as compared with the nonsinter scaffold. This sinter scaffold also significantly supported viability and differentiation of the MC3T3-E1 preosteoblast cells (p < 0.05). The marked expression of Col1α1 and osteocalcin (OCN) osteoblast markers were also observed after 14 days of incubation (p < 0.05). The sinter scaffold supported attachment, viability, and differentiation of preosteoblast cells. Hence, sinter hydroxyapatite scaffold from nacreous layer is a promising biomaterial for bone tissue engineering.

Three dimensionally printed pearl powder/poly-caprolactone composite scaffolds for bone regeneration

Pearl has great potential as a natural biomaterial for bone tissue engineering, but it suffers from low porosity, difficulty in molding, and poor anti-buckling property. In this study, we used the 3-D printing technique to fabricate original pearl powder and PCL composite scaffolds with different concentrations of pearl powder. The four groups of scaffolds were termed PCL, 30% Pearl/PCL, 50% Pearl/PCL and 80% Pearl/PCL scaffolds according to the proportion of pearl powder. The samples were systematically investigated by scanning electron microscopy (SEM), wide-angle XRD, liquid substitution, Zwick static materials testing, and energy dispersive X-ray analysis. Biological characterization included SEM, fluorescent staining using calcein-AM, cell counting kit-8 assay, alkaline phosphatase and qRT-PCR analysis. The results show that the pore size and the pore morphology of the scaffolds are closely controlled via 3-D printing. This is very beneficial for tissue growth and nutrition transmission. The regular and uniform square macropore structure ensured that the pearl powder/PCL scaffolds had favorable mechanical strength. As the concentration of pearl powder in the scaffolds increase, the compressive strength and apatite formation increase as well as cell adhesion, proliferation, and osteogenic differentiation. These results show that pearl powder/PCL scaffolds fit the requirements of bone tissue engineering. The structures as well as physicochemical and biological properties of pearl powder/PCL composite scaffolds are positively associated with pearl powder concentrations.

Water‑soluble nano‑pearl powder promotes MC3T3‑E1 cell differentiation by enhancing autophagy via the MEK/ERK signaling pathway

Nacre (mother of pearl) is a bioactive material capable of facilitating osteoblast proliferation and differentiation; however, further investigation into the mechanism underlying the effects of nacre on the stimulation of bone differentiation is required. The present study aimed to elucidate the effects of water‑soluble nano‑pearl powder (WSNNP) on osteoblast differentiation and to examine the underlying mechanisms. A MTT assay revealed that WSNNP (10, 25 and 50 µg/ml) may stimulate the viability of preosteoblastic MC3T3‑E1 cells and 50 µg/ml WSNNP exhibited the maximum stimulatory effect. Furthermore, WSNNP significantly enhanced the protein expression levels of differentiation markers, including collagen I, runt‑related transcription factor 2 (RUNX2), secreted phosphoprotein1 (SPP1) and alkaline phosphatase (ALP) in a dose‑dependent manner, which indicated that WSNNP may promote osteoblast differentiation. Subsequently, whether autophagy serves a role in WSNNP‑mediated differentiation of osteoblasts was investigated via western blotting and immunofluorescence. The results of the present study demonstrated that WSNNP treatment significantly evoked the expression of autophagy markers, including microtubule‑associated light chain 3 (LC3)II/I, Beclin1 and autophagy‑related 7 (ATG7), whereas the autophagy inhibitor 3‑methyladenine significantly inhibited WSNNP‑induced osteoblast differentiation. Furthermore, the role of WSNNP on the potential signaling pathways that activate autophagy was investigated. The present study reported that WSNNP may significantly upregulate the mitogen‑activated protein kinase kinase (MEK)/extracellular signal‑regulated kinase (ERK) signaling pathway. Treatment with the MEK inhibitor U0126 significantly inhibited the protein expression levels of WSNNP‑induced differentiation markers, including collagen I, RUNX2, SPP1 and ALP, and autophagy markers, including LC3II/I, Beclin1 and ATG7. Therefore, the findings of the present study suggested that WSNNP may contribute to osteoblast differentiation by enhancing autophagy via the MEK/ERK signaling pathway, thus suggesting a novel direction for optimizing the biological materials in bone implants.

Design strategies and applications of nacre-based biomaterials

The field of tissue engineering and regenerative medicine relies heavily on materials capable of implantation without significant foreign body reactions and with the ability to promote tissue differentiation and regeneration. The field of bone tissue engineering in particular requires materials capable of providing enhanced mechanical properties and promoting osteogenic cell lineage commitment. While bone repair has long relied almost exclusively on inorganic, calcium phosphate ceramics such as hydroxyapatite and their composites or on non-degradable metals, the organically derived shell and pearl nacre generated by mollusks has emerged as a promising alternative. Nacre is a naturally occurring composite material composed of inorganic, calcium carbonate plates connected by a framework of organic molecules. Similar to mammalian bone, the highly organized microstructure of nacre endows the composite with superior mechanical properties while the organic phase contributes to significant bioactivity. Studies, both in vitro and in vivo, have demonstrated nacre's biocompatibility, biodegradability, and osteogenic potential, which are superior to pure inorganic minerals such as hydroxyapatite or non-degradable metals. Nacre can be used directly as a bulk implant or as part of a composite material when combined with polymers or other ceramics. While nacre has demonstrated its effectiveness in multiple cell culture and animal models, it remains a relatively underexplored biomaterial. This review introduces the formation, structure, and characteristics of nacre, and discusses the present and future uses of this biologically-derived material as a novel biomaterial for orthopedic and other tissue engineering applications.

STATEMENT OF SIGNIFICANCE

Mussel derived nacre, a biological composite composed of mineralized calcium carbonate platelets and interplatelet protein components, has recently gained interest as a potential alternative ceramic material in orthopedic biomaterials, combining the integration and mechanical capabilities of calcium phosphates with increased bioactivity derived from proteins and biomolecules; however, there is limited awareness of this material's potential. Herein, we present, to our knowledge, the first comprehensive review of nacre as a biomaterial. Nacre is a highly promising yet overlooked biomaterial for orthopedic tissue engineering with great potential in a wide variety of material systems. It is our hope that publication of this article will lead to increased community awareness of the potential of nacre as a versatile, bioactive ceramic capable of improving bone tissue regeneration and will elicit increased research effort and innovation utilizing nacre.

Shotgun proteomics analysis of proliferating STRO-1-positive human dental pulp cell after exposure to nacreous water-soluble matrix

INTRODUCTION

For dental treatment, dentin regeneration is required after a tooth injury with dental pulp exposure. The effects of the water-soluble matrix (WSM) extracted from the nacreous layer of the bivalve Pinctada maxima on human dental pulp cells in vitro were challenging and useful for clinical application.

MATERIAL AND METHODS

The biological activity of the STRO-1-positive human dental pulp cells in response to WSM compared to Dulbecco's modified Eagle medium (DMEM) as a normal control was monitored. The cell survival rate was analyzed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Proteomic profiles among inducers and noninducers with time dependency were compared by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis combined with liquid chromatography-tandem mass spectrometry (GeLC-MS/MS).

RESULTS

The human dental pulp cells cultured in nacreous WSM exhibited higher relative cell viability than those in DMEM with similar morphological appearance. Significant changes were found in the relative abundance of 44 proteins in cells after exposure to WSM for 2 weeks. They play a role in cell adhesion, cell proliferation, metabolic process, signal transduction, stress response, transcription, translation, and transport.

CONCLUSION

These results indicate that WSM of P. maxima has the ability to induce proliferation of human dental pulp cells.

CLINICAL RELEVANCE

This finding initiated the study to evaluate the suitability of nacre as biomaterial for dentistry.