Dental pulp stem cells: Novel cell-based and cell-free therapy for peripheral nerve repair

Application of dental pulp stem cells for bone regeneration

Bone defects resulting from severe trauma, tumors, inflammation, and other factors are increasingly prevalent. Stem cell-based therapies have emerged as a promising alternative. Dental pulp stem cells (DPSCs), sourced from dental pulp, have garnered significant attention owing to their ready accessibility and minimal collection-associated risks. Ongoing investigations into DPSCs have revealed their potential to undergo osteogenic differentiation and their capacity to secrete a diverse array of ontogenetic components, such as extracellular vesicles and cell lysates. This comprehensive review article aims to provide an in-depth analysis of DPSCs and their secretory components, emphasizing extraction techniques and utilization while elucidating the intricate mechanisms governing bone regeneration. Furthermore, we explore the merits and demerits of cell and cell-free therapeutic modalities, as well as discuss the potential prospects, opportunities, and inherent challenges associated with DPSC therapy and cell-free therapies in the context of bone regeneration.

The Combined Effects on Human Dental Pulp Stem Cells of Fast-Set or Premixed Hydraulic Calcium Silicate Cements and Secretome Regarding Biocompatibility and Osteogenic Differentiation

An important part of regenerative endodontic procedures involving immature permanent teeth is the regeneration of the pulp-dentin complex with continuous root development. Hydraulic calcium silicate cements (HCSCs) are introduced for the pulpal treatment of immature permanent teeth. The stem-cell-derived secretome recently has been applied for the treatment of various damaged tissues. Here, we evaluated the biocompatibility and osteogenic differentiation of HCSCs combined with secretome on human dental pulp stem cells. In the Cell Counting Kit-8 test and wound healing assays, significantly higher cell viability was observed with secretome application. In alkaline phosphatase analysis, the activity was significantly higher with secretome application in all groups, except for RetroMTA on day 2 and Endocem MTA Premixed on day 4. In an Alizarin Red S staining analysis, all groups with secretome application had significantly higher staining values. Quantitative real-time polymerase chain reaction results showed that the day 7 expression of OSX significantly increased with secretome application in all groups. SMAD1 and DSPP expression also increased significantly with secretome addition in all groups except for Biodentine. In conclusion, HCSCs showed favorable biocompatibility and osteogenic ability and are predicted to demonstrate greater synergy with the addition of secretome during regenerative endodontic procedures involving immature permanent teeth.

The Effect of Calcium hydroxide, Glass Ionomer and light cured resin modified calcium silicate on viability, proliferation and differentiation of stem cells from human exfoliated deciduous teeth

BACKGROUND

Vital pulp therapy, based on the use of stem cells, has promising research and therapeutic applications in dentistry. It is essential to understand the direct effect of capping materials on the dental pulp stem cells of primary teeth, which contribute to the healing powers of the tooth. The aim of this study is to evaluate the effect of different capping materials (Calcium Hydroxide (DyCal®) - Glass Ionomer (Fuji IX®) and light-cured resin modified calcium silicate (TheraCal LC®)) on the viability, proliferation, and differentiation of stem cells from human exfoliated deciduous teeth (SHEDs).

METHODS

SHEDs were isolated from extracted primary teeth, then divided into four groups and each of the capping materials were applied to the stem cells as follows: group I the controls, group II with Ca(OH)2, group III with the GIC, and group IV with the Theracal LC. For all groups assessment of viability and proliferation rate was done using the MTT cell proliferation assay. Also, Differentiation was evaluated by measuring the gene expression of Alkaline phosphatase enzyme activity (ALP) and Dentin matrix protein-1 (DMP1) through quantitative real-time PCR. Morphological assessment was conducted using Alizarin Red S staining. All evaluations were performed after 7 and 14 days of culture.

RESULTS

TheraCal LC showed the highest values of proliferation, which was significant only compared to the control group after 2 weeks (p = 0.012). After one week, TheraCal LC showed the highest significant values of ALP and DMP1 compared to all other groups (p < 0.001).

CONCLUSION

The three materials under study are biocompatible, maintain viability, and stimulate the proliferation and differentiation of SHEDs. However, TheraCal LC allows better proliferation of SHEDs than Dycal Ca(OH)2 and Fuji IX GIC.

Comparative proteomics analysis of transforming growth factor-beta1-overexpressed human dental pulp stem cell-derived secretome on CD44-mediated fibroblast activation via canonical smad signal pathway

PURPOSE

The aim of this study investigates whether the secretome collected from human dental pulp stem cells (hDPSCs) transfected with transforming growth factor-beta1 (TGF-β1) is related to CD44 expression of fibroblasts and canonical smad signaling pathway via proteomic analyzes.

MATERIALS AND METHODS

In order to obtain secretome, hDPSCs were conditioned with serum-free alpha-MEM in an incubator containing 37°C, 5% CO₂, and humidity for 18-24 h. Proteins in control and TGF-β1 secretome were analyzed by tandem mass spectrometry-based shotgun proteomic method. Bioinformatic evaluations were completed via Ingenuity Pathway Analysis (IPA, QIAGEN) software. CD44 expressions in fibroblasts were evaluated by real time-PCR, western blot, and immunofluorescent staining. The relationship of canonical smad pathway and CD44 was analyzed by western blot and LC-MS/MS. Cell cycle, proliferation and wound healing tests were performed in the secretome groups.

RESULTS

Venn diagram was showed 174 common proteins were identified from each group. In the control secretome 140 unique proteins were identified and 66 entries were exclusive for TGF-β1 secretome. CD44 gene and protein expressions were increased in fibroblasts treated with TGF-β1 secretome. Relationship between targeted protein data showed that activation of the canonical TGF-β1/Smad pathway was up-regulated CD44 expression in fibroblasts. The canonical smad pathway-mediated upregulation of CD44 may increase the mitotic activity, proliferation, and wound healing potential in fibroblasts.

CONCLUSION

While TGF-β1-transfected hDPSC secretome may be a potential therapeutic candidate in regenerative connective tissue therapies as it induces fibroblast activation, anti-TGF-β1-based therapies would be considered in histopathological conditions such as pulmonary fibrosis or hepatic fibrosis.

Application of Biocompatible Scaffolds in Stem-Cell-Based Dental Tissue Engineering

Tissue engineering as an important field in regenerative medicine is a promising therapeutic approach to replace or regenerate injured tissues. It consists of three vital steps including the selection of suitable cells, formation of 3d scaffolds, and adding growth factors. Mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs) are mentioned as two main sources for this approach that have been used for the treatment of various types of disorders. However, the main focus of literature in the field of dental tissue engineering is on utilizing MSCs. On the other hand, biocompatible scaffolds play a notable role in this regenerative process which is mentioned to be harmless with acceptable osteoinductivity. Their ability in inhibiting inflammatory responses also makes them powerful tools. Indeed, stem cell functions should be supported by biomaterials acting as scaffolds incorporated with biological signals. Naturally derived polymeric scaffolds and synthetically engineered polymeric/ceramic scaffolds are two main types of scaffolds regarding their materials that are defined further in this review. Various strategies of tissue bioengineering can affect the regeneration of dentin-pulp complex, periodontium regeneration, and whole teeth bioengineering. In this regard, in vivo/ex vivo experimental models have been developed recently in order to perform preclinical studies of dental tissue engineering which make it more transferable to be used for clinic uses. This review summarizes dental tissue engineering through its different components. Also, strategies of tissue bioengineering and experimental models are introduced in order to provide a perspective of the potential roles of dental tissue engineering to be used for clinical aims.

Effects of non-steroidal anti-inflammatory drug (ibuprofen) in low and high dose on stemness and biological characteristics of human dental pulp-derived mesenchymal stem cells

PURPOSE

The effect of ibuprofen, an NSAID, on biological characteristics such as proliferation, viability, DNA damage and cell cycle in dental pulp derived stem cells (DPSCs) can be important for regenerative medicine. Our aim is to investigate how low and high doses of ibuprofen affect stem cell characteristics in DPSCs.

MATERIALS AND METHODS

DPSCs were isolated from human teeth and characterized by flow cytometry and differentiation tests. Low dose (0.1 mmol/L) and high dose (3 mmol/L) ibuprofen were administered to DPSCs. Surface markers between groups were analyzed by immunofluorescence staining. Membrane depolarization, DNA damage, viability and cell cycle analysis were performed between groups using biological activity test kits. Cellular proliferation was measured by the MTT and cell count kit. Statistical analyzes were performed using GraphPad Prism software.

RESULTS

High dose ibuprofen significantly increased CD44 and CD73 expression in DPSCs. High-dose ibuprofen significantly reduced mitochondrial membrane depolarization in DPSCs. It was determined that DNA damage in DPSCs decreased significantly with high dose ibuprofen. Parallel to this, cell viability increased significantly in the ibuprofen applied groups. High-dose ibuprofen was found to increase mitotic activity in DPSCs. Proliferation in DPSCs increased in parallel with the increase in mitosis stage because of high-dose ibuprofen administration compared to the control and low-dose ibuprofen groups. Our proliferation findings appeared to support cell cycle analyses.

CONCLUSION

High dose ibuprofen improved the immunophenotypes and biological activities of DPSCs. The combination of ibuprofen in the use of DPSCs in regenerative medicine can make stem cell therapy more effective.

Transforming growth factor β1-enriched secretome up-regulate osteogenic differentiation of dental pulp stem cells, and a potential therapeutic for gingival wound healing: A comparative proteomics study

OBJECTIVES

Current study aimed at comparing the human dental pulp-derived stem cell (hDPSC) secretome (Control secretome) and transforming growth factor beta1 (TGF-β1)-transfected hDPSC secretome (TGF-β1 Secretome), which have the potential to be therapeutic in terms of regenerative dentistry, in terms of osteogenesis, adipogenesis and gingival wound healing with proteomic analyses.

MATERIALS AND METHODS

pCMV-TGF-β1 plasmid was transfected into hDPSCs by electroporation. hDPSC and TGF-β1 transfected hDPSC secretomes were collected for LC-MS/MS. Protein contents in control secretome and TGF-β1 secretome were analyzed by tandem mass spectrometry-based shotgun proteomic method. Bioinformatic evaluations for canonical pathways, upstream regulators and networks were completed via Ingenuity Pathway Analysis (IPA, QIAGEN) software. Surface marker expressions between groups, treated secretome were measured by flow cytometry. To support the proteomic data morphologically, we performed osteogenic-adipogenic differentiation in hDPSCs treated with control secretome and TGF-β1 secretome, and scratch wound healing assay in gingival fibroblasts. Statistical analyses were performed by GraphPad Prism 8.02.

RESULTS

Venn diagram classification showed us 174 common proteins were identified from each group. In the control secretome 140 unique proteins were identified and 66 entries were exclusive for TGF-β1 secretome. TGF-β1 secretome was found to have therapeutic effect on MSC-specific immunophenotypes. TGF-β1 secretome was determined to up-regulate osteogenesis-related molecules and pathways while down-regulating adipogenesis-related pathways. Analysis of canonical pathways showed that TGF-β1 secretome is associated with the wound healing pathway.

CONCLUSION

Our study provided the first evidence that proteins identified in TGF-β1-transfected hDPSC secretomes are potential regulators of osteogenic/adipogenic differentiation and fibroblast wound healing.

CLINICAL SIGNIFICANCE

Based on these results, TGF-β1 secretome may have a therapeutic effect in repairing osteoporosis-related bone injuries, wound healing of oral mucosa and gingival tissue. TGF-β1 secretome may be a potential cell-free therapeutic in orthopedics and regenerative dentistry.

Transplanted neural lineage cells derived from dental pulp stem cells promote peripheral nerve regeneration

Cell therapy for peripheral nerve injury is a promising strategy as regenerative medicine that restores neurological function. However, challenges remain in producing suitable and sufficient amounts of autologous cells for promoting nerve regeneration. This study aimed to identify the characteristics of neural lineage cells (NLCs) differentiated from dental pulp stem cells (DPSCs) and reveal their effect on functional recovery and nerve regeneration after cell transplantation into an immunodeficient rat using a nerve guide conduit. Here we report a protocol of neural induction in monolayer culture and characterize NLCs in vitro. Furthermore, NLCs were transplanted into an immunodeficient rat model with a 10-mm sciatic nerve defect, and cell survival and differentiation were investigated in vivo. Outcomes of nerve regeneration were also assessed using the remyelinated axon numbers, myelin sheath thickness, electrophysiological activities, and gastrocnemius muscle mass. NLCs comprised neuronal, astrocyte, oligodendrocyte, and neural crest lineage cells. NLCs enhanced the activities of endothelial cells, Schwann cells, and neurons in a paracrine-dependent manner in vitro. At 2 weeks post-transplantation, numerous transplanted NLCs differentiated into platelet-derived growth factor receptor alpha (PDGFRα) + oligodendrocyte progenitor cells (OPCs) and a few PDGFRα + /p75 neurotrophin receptor + Schwann cell-like cells derived from OPCs were observed. At 12 weeks post-transplantation, human Schwann cell-like cells survived, and axon growth, remyelination, electrophysiological activities, and muscle atrophy were improved. This study demonstrates the broad application of our protocol of neural induction of DPSCs and portrays the efficacy of transplantation of NLCs derived from human DPSCs as a promising strategy for peripheral nerve regeneration.

Dental Pulp Stem Cell-Derived Secretome and Its Regenerative Potential

The therapeutic potential of the dental pulp stem (DSC) cell-derived secretome, consisting of various biomolecules, is undergoing intense research. Despite promising in vitro and in vivo studies, most DSC secretome-based therapies have not been implemented in human medicine because the paracrine effect of the bioactive factors secreted by human dental pulp stem cells (hDPSCs) and human exfoliated deciduous teeth (SHEDs) is not completely understood. In this review, we outline the current data on the hDPSC- and SHED-derived secretome as a potential candidate in the regeneration of bone, cartilage, and nerve tissue. Published reports demonstrate that the dental MSC-derived secretome/conditional medium may be effective in treating neurodegenerative diseases, neural injuries, cartilage defects, and repairing bone by regulating neuroprotective, anti-inflammatory, antiapoptotic, and angiogenic processes through secretome paracrine mechanisms. Dental MSC-secretomes, similarly to the bone marrow MSC-secretome activate molecular and cellular mechanisms, which determine the effectiveness of cell-free therapy. Many reports emphasize that dental MSC-derived secretomes have potential application in tissue-regenerating therapy due to their multidirectional paracrine effect observed in the therapy of many different injured tissues.

Electromagnetic field-assisted cell-laden 3D printed poloxamer-407 hydrogel for enhanced osteogenesis

3D bioprinted hydrogel has gained enormous attention, especially in tissue engineering, owing to its attractive structure and excellent biocompatibility. In this study, we demonstrated that 3D bioprinted cell-laden 'thermoresponsive' poloxamer-407 (P407) gels have the potential to stimulate osteogenic differentiation of apical papilla stem cells (SCAPs) under the influence of low voltage-frequency (5 V-1 Hz, 0.62 mT) electromagnetic fields (EMFs). SCAPs were initially used for cell-laden 3D printing to biomimic the apical papilla of human teeth. The developed hydrogel exhibited higher mechanical strength as well as good printability, showing high-quality micro-architecture. Moreover, the as-printed hydrogels (5 mm × 5 mm) were loaded with plasminogen activator inhibitor-1 (PAI-1) for testing the combined effect of PAI-1 and EMFs on SCAP differentiation. Interestingly, the 3D hydrogels showed improved viability and differentiation of SCAPs under EMFs' influence as examined by live/dead assay and alizarin Red-S staining, respectively. Therefore, our results confirmed that P407 hydrogels are non-toxic for encapsulation of SCAPs, yielding high cell viability and accelerate the cell migration potential. The 3D hydrogels with PAI-1 exhibited high mRNA expression levels for osteogenic/odontogenic gene markers (ALP, Col-1, DSPP, and DMP-1) vis-à-vis control after 14 days of in vitro culture. Our findings suggest that 3D bioprinted P407 hydrogels are biocompatible for SCAP encapsulation, and the applied low voltage-frequency EMFs could effectively improve dental tissue regeneration, particularly for oral applications.

Identification of secreted factors in dental pulp cell-conditioned medium optimized for neuronal growth

With their potent regenerative and protective capacities, stem cell-derived conditioned media emerged as an effective alternative to cell therapy, and have a prospect to be manufactured as pharmaceutical products for tissue regeneration applications. Our study investigates the neuroregenerative potential of human dental pulp cells (DPCs) conditioned medium (CM) and defines an optimization strategy of DPC-CM for enhanced neuronal outgrowth. Primary sensory neurons from mouse dorsal root ganglia were cultured with or without DPC-CM, and the lengths of βIII-tubulin positive neurites were measured. The impacts of several manufacturing features as the duration of cell conditioning, CM storage, and preconditioning of DPCs with some factors on CM functional activity were assessed on neurite length. We observed that DPC-CM significantly enhanced neurites outgrowth of sensory neurons in a concentration-dependent manner. The frozen storage of DPC-CM had no impact on experimental outcomes and 48 h of DPC conditioning is optimal for an effective activity of CM. To further understand the regenerative feature of DPC-CM, we studied DPC secretome by human growth factor antibody array analysis and revealed the presence of several factors involved in either neurogenesis, neuroprotection, angiogenesis, and osteogenesis. The conditioning of DPCs with the B-27 supplement enhanced significantly the neuroregenerative effect of their secretome by changing its composition in growth factors. Here, we show that DPC-CM significantly stimulate neurite outgrowth in primary sensory neurons. Moreover, we identified secreted protein candidates that can potentially promote this promising regenerative feature of DPC-CM.

The effect of electromagnetic fields on survival and proliferation rate of dental pulp stem cells

Aims: Extremely low-frequency electromagnetic fields (ELF-EMF) can affect biological systems and alter some cell functions like proliferation rate. Dental pulp tissue is known as a source of multipotent stromal stem cells (MSCs), which can be obtained by a less invasive and more available process compared to bone marrow-derived stem cells (BMSCs). This study aimed to consider the effect of ELF-EMF on proliferation rates of human dental pulp stem cells (hDPSCs).Material and methods: ELF-EMF was generated by a system including autotransformer, multi-meter, solenoid coils, teslameter and its probe. The effect of ELF-EMF with the intensity of 0.5 and 1 mT and 50 Hz on the proliferation rate of hDPSCs was assessed in 20 and 40 min per day for 7 days. MTT assay and DAPI test were used to determine the growth and proliferation of DPSCs.Results: Based on MTT, ELF-EMF has maximum effect with the intensity of 1 mT for 20 min/day on the proliferation of hDPSCs. The survival and proliferation rate in all exposure groups were significantly higher than the control group. Based on the data obtained from MTT and DAPI assay, the number of viable cells in the group exposed to 1 mT for 20 min/day was higher than other groups (p < .05).Conclusions: Regarding to the results of this study, 0.5 and 1 mT ELF-EMF can enhance survival and proliferation rates of hDPSCs.

Dental mesenchymal stem cells and neuro-regeneration: a focus on spinal cord injury

Regenerative medicine is a branch of translational research that aims to reestablish irreparably damaged tissues and organs by stimulating the body's own repair mechanisms via the implantation of stem cells differentiated into specialized cell types. A rich source of adult stem cells is located inside the tooth and is represented by human dental pulp stem cells, or hDPSCs. These cells are characterized by a high proliferative rate, have self-renewal and multi-lineage differentiation properties and are often used for tissue engineering and regenerative medicine. The present review will provide an overview of hDPSCs and related features with a special focus on their potential applications in regenerative medicine of the nervous system, such as, for example, after spinal cord injury. Recent advances in the identification and characterization of dental stem cells and in dental tissue engineering strategies suggest that bioengineering approaches may successfully be used to regenerate districts of the central nervous system, previously considered irreparable.

The advances in nerve tissue engineering: From fabrication of nerve conduit to in vivo nerve regeneration assays

Peripheral nerve damage is a common clinical complication of traumatic injury occurring after accident, tumorous outgrowth, or surgical side effects. Although the new methods and biomaterials have been improved recently, regeneration of peripheral nerve gaps is still a challenge. These injuries affect the quality of life of the patients negatively. In the recent years, many efforts have been made to develop innovative nerve tissue engineering approaches aiming to improve peripheral nerve treatment following nerve injuries. Herein, we will not only outline what we know about the peripheral nerve regeneration but also offer our insight regarding the types of nerve conduits, their fabrication process, and factors associated with conduits as well as types of animal and nerve models for evaluating conduit function. Finally, nerve regeneration in a rat sciatic nerve injury model by nerve conduits has been considered, and the main aspects that may affect the preclinical outcome have been discussed.