The potential use of enamel matrix derivative for in situ anterior cruciate ligament tissue engineering: a translational in vitro investigation

A tyrosine-rich amelogenin peptide promotes neovasculogenesis in vitro and ex vivo

The formation of new blood vessels has been shown to be fundamental in the repair of many damaged tissues, and we have recently shown that the adult human periodontal ligament contains multipotent stem/progenitor cells that are capable of undergoing vasculogenic and angiogenic differentiation in vitro and ex vivo. Enamel matrix protein (EMP) is a heterogeneous mixture of mainly amelogenin-derived proteins produced during tooth development and has been reported to be sometimes effective in stimulating these processes, including in clinical regeneration of the periodontal ligament. However, the identity of the specific bioactive component of EMP remains unclear. In the present study we show that, while the high-molecular-weight Fraction A of enamel matrix derivative (a heat-treated form of EMP) is unable to stimulate the vasculogenic differentiation of human periodontal ligament cells (HPC) in vitro, the low-molecular-weight Fraction C significantly up-regulates the expression of the endothelial markers VEGFR2, Tie-1, Tie-2, VE-cadherin and vWF and markedly increases the internalization of low-density lipoprotein. Furthermore, we also demonstrate, for the first time, that the synthetic homolog of the 45-amino acid tyrosine-rich amelogenin peptide (TRAP) present in Fraction C is likely to be responsible for its vasculogenesis-inducing activity. Moreover, the chemically synthesized TRAP peptide is also shown here to be capable of up-regulating the angiogenic differentiation of the HPC, based on its marked stimulation of in vitro cell migration and tubule formation and of blood vessel formation assay in a chick embryo chorioallantoic membrane model ex vivo. This novel peptide, and modified derivatives, might thereby represent a new class of regenerative drug that has the ability to elicit new blood vessel formation and promote wound healing in vivo.

A preliminary study on amelogenin-loaded electrospun scaffolds

Amelogenin is a major enamel matrix protein onto which developing enamel forms. In the realm of tissue engineering, amelogenin has been studied and applied to periodontal and wound healing applications. This study introduces the first attempts of incorporating amelogenin within an electrospun scaffold. Amelogenin was extracted from porcine unerupted tooth buds and electrospun with poly(glycolic acid) and poly(ϵ-caprolactone). Protein release kinetics, mechanical properties, fiber diameter, mineralization potential, and cell adhesion properties of the amelogenin-blended scaffolds were studied and compared to the electrospun poly(glycolic acid) and poly(ϵ-caprolactone) controls. Electrospun scaffolds loaded with amelogenin were incubated in phosphate buffer saline. Protein quantification and morphological and mechanical analyses were conducted on the degraded scaffolds, and the incubated phosphate buffer saline was also tested for protein content. Fresh scaffolds were incubated overnight in conventional simulated body fluid to evaluate mineralization potential of the incorporated electrospun amelogenin. Human dermal fibroblasts were seeded onto scaffolds, incubated overnight, cryosectioned, and stained with 4′,6-diamidino-2-phenylindole to determine cellular adhesive properties. The incorporation of 5 mg/mL amelogenin into electrospun scaffolds improved mechanical properties (in poly(ϵ-caprolactone) scaffolds), increased fiber mineralization (in poly(glycolic acid) scaffolds), and improved human dermal fibroblast adhesion (in poly(ϵ-caprolactone) scaffolds). The presented results suggest that amelogenin can be used for multiple tissue engineering applications in the form of an additive to an electrospun scaffold.

Effects of enamel matrix proteins on multi-lineage differentiation of periodontal ligament cells in vitro

The adult periodontal ligament (PDL) is considered to contain progenitor cells that are involved in the healing of periodontal wounds. Treatment with enamel matrix derivative (EMD), a heat-treated preparation derived from enamel matrix proteins (EMPs), has been shown to be of some clinical benefit in eliciting periodontal regeneration in vivo. Although there is extensive information available about the effects of EMD on periodontal regeneration, the precise influence of this material on alveolar bone and the formation of blood vessels and proprioceptive sensory nerves, prominent features of functionally active periodontal tissue, remain unclear. The aim of the present study was therefore to examine the effects of EMD on the ability of human periodontal ligament cells (HPCs) to undergo multi-lineage differentiation in vitro. Our results showed that HPCs treated with EMD under non-selective growth conditions did not show any evidence of osteogenic, adipogenic, chondrogenic, neovasculogenic, neurogenic and gliogenic "terminal" differentiation. In contrast, under selective lineage-specific culture conditions, EMD up-regulated osteogenic, chondrogenic and neovasculogenic genes and "terminal" differentiation, but suppressed adipogenesis, neurogenesis and gliogenesis. These findings thus demonstrate for the first time that EMD can differentially modulate the multi-lineage differentiation of HPCs in vitro.

Acceleration of tendon–bone healing in anterior cruciate ligament reconstruction using an enamel matrix derivative in a rat model

We examined whether enamel matrix derivative (EMD) could improve healing of the tendon–bone interface following reconstruction of the anterior cruciate ligament (ACL) using a hamstring tendon in a rat model. ACL reconstruction was performed in both knees of 30 Sprague-Dawley rats using the flexor digitorum tendon. The effect of commercially available EMD (EMDOGAIN), a preparation of matrix proteins from developing porcine teeth, was evaluated. In the left knee joint the space around the tendon–bone interface was filled with 40 µl of EMD mixed with propylene glycol alginate (PGA). In the right knee joint PGA alone was used. The ligament reconstructions were evaluated histologically and biomechanically at four, eight and 12 weeks (n = 5 at each time point). At eight weeks, EMD had induced a significant increase in collagen fibres connecting to bone at the tendon–bone interface (p = 0.047), whereas the control group had few fibres and the tendon–bone interface was composed of cellular and vascular fibrous tissues. At both eight and 12 weeks, the mean load to failure in the treated specimens was higher than in the controls (p = 0.009). EMD improved histological tendon–bone healing at eight weeks and biomechanical healing at both eight and 12 weeks. EMD might therefore have a human application to enhance tendon–bone repair in ACL reconstruction.

Future dentistry: cell therapy meets tooth and periodontal repair and regeneration

Cell-based tissue repair of the tooth and – tooth-supporting – periodontal ligament (PDL) is a new attractive approach that complements traditional restorative or surgical techniques for replacement of injured or pathologically damaged tissues. In such therapeutic approaches, stem cells and/or progenitor cells are manipulated in vitro and administered to patients as living and dynamic biological agents. In this review, we discuss the clonogenic potential of human dental and periodontal tissues such as the dental pulp and the PDL and their potential for tooth and periodontal repair and/or regeneration. We propose novel therapeutic approaches using stem cells or progenitor cells, which are targeted to regenerate the lost dental or periodontal tissue.

A review on endogenous regenerative technology in periodontal regenerative medicine

Periodontitis is a globally prevalent inflammatory disease that causes the destruction of the tooth-supporting apparatus and potentially leads to tooth loss. Currently, the methods to reconstitute lost periodontal structures (i.e. alveolar bone, periodontal ligament, and root cementum) have relied on conventional mechanical, anti-infective modalities followed by a range of regenerative procedures such as guided tissue regeneration, the use of bone replacement grafts and exogenous growth factors (GFs), and recently developed tissue engineering technologies. However, all current or emerging paradigms have either been shown to have limited and variable outcomes or have yet to be developed for clinical use. To accelerate clinical translation, there is an ongoing need to develop therapeutics based on endogenous regenerative technology (ERT), which can stimulate latent self-repair mechanisms in patients and harness the host's innate capacity for regeneration. ERT in periodontics applies the patient's own regenerative 'tools', i.e. patient-derived GFs and fibrin scaffolds, sometimes in association with commercialized products (e.g. Emdogain and Bio-Oss), to create a material niche in an injured site where the progenitor/stem cells from neighboring tissues can be recruited for in situ periodontal regeneration. The choice of materials and the design of implantable devices influence therapeutic potential and the number and invasiveness of the associated clinical procedures. The interplay and optimization of each niche component involved in ERT are particularly important to comprehend how to make the desired cell response safe and effective for therapeutics. In this review, the emerging opportunities and challenges of ERT that avoid the ex vivo culture of autologous cells are addressed in the context of new approaches for engineering or regeneration of functional periodontal tissues by exploiting the use of platelet-rich products and its associated formulations as key endogenous resources for future clinical management of periodontal tissue defects.

Enamel matrix proteins; old molecules for new applications

Emdogain (enamel matrix derivative, EMD) is well recognized in periodontology, where it is used as a local adjunct to periodontal surgery to stimulate regeneration of periodontal tissues lost to periodontal disease. The biological effect of EMD is through stimulation of local growth factor secretion and cytokine expression in the treated tissues, inducing a regenerative process that mimics odontogenesis. The major (>95%) component of EMD is Amelogenins (Amel). No other active components have so far been isolated from EMD, and several studies have shown that purified amelogenins can induce the same effect as the complete EMD. Amelogenins comprise a family of highly conserved extracellular matrix proteins derived from one gene. Amelogenin structure and function is evolutionary well conserved, suggesting a profound role in biomineralization and hard tissue formation. A special feature of amelogenins is that under physiological conditions the proteins self-assembles into nanospheres that constitute an extracellular matrix. In the body, this matrix is slowly digested by specific extracellular proteolytic enzymes (matrix metalloproteinase) in a controlled process, releasing bioactive peptides to the surrounding tissues for weeks after application. Based on clinical and experimental observations in periodontology indicating that amelogenins can have a significant positive influence on wound healing, bone formation and root resorption, several new applications for amelogenins have been suggested. New experiments now confirm that amelogenins have potential for being used also in the fields of endodontics, bone regeneration, implantology, traumatology, and wound care.