Human Dental Pulp Stem Cells: Do They Hold Potential for Orthopaedics?

Angelo Vasileios Vasiliadis, MD, MSc, PhD, GREECE Vasiliki Boka, MD, GREECE Theodorakys Marín Fermín, MD, VENEZUELA

ISAKOS Newsletter   Current Perspective 2024   Not yet rated

Introduction

Stem cells are unspecialized cells that retain the ability to renew themselves through cell division and can further differentiate into various types of specialized cells, such as osteocytes, chondrocytes, adipocytes, muscle cells, and hepatocytes. These stem cells can be found in many adult tissues, including skin, adipose tissue, peripheral blood, bone marrow, salivary gland, and dental pulp.

Recently, stem cell therapies have become a promising and advanced scientific research field because of their usefulness in regenerative medicine, improving patients’ quality of life and prolonging survival rates. Clinical studies have tested using mesenchymal stem cells (MSCs) of dental origin as candidates for cellular therapy of stomatognathic disorders, maxillofacial reconstruction, bone-related diseases, and orthopaedic procedures.

Dental Pulp Stem Cells: Characteristics

Although many studies have shown that bone marrow- and adipose-derived MSCs are the mainstay of regenerative cell therapies in orthopaedics, human dental stem cells have recently gained more popularity due to their potential. Human dental pulp stem cells (hDPSCs) show mesenchymal stem cell features, differentiating into dentin in vitro and dentin-pulp-like complex in vivo and presenting osteogenic and chondrogenic potential capacity.

To date, bone marrow-derived stem cells have shown the highest osteogenic differentiation potential by expressing high levels of CD90, making them more suitable for bone repair and regeneration. At the same time, adipose-derived MSCs are more prone to differentiate into adipocytes with relatively limited chondrogenic potential, like those of the umbilical cord. However, hDPSCs have demonstrated higher clonogenic and proliferative potential than bone marrow MSCs (higher population doubling and lower population doubling time) and show immunomodulation and antiinflammatory properties in the local environment.

Moreover, compared with other sources, such as bone marrow and umbilical cord-derived MSCs, hDPSCs can be easily and safely isolated from teeth with low morbidity and no ethical concerns. Moreover, further types of dental MSC populations can be harvested from human exfoliated deciduous teeth (SHED, which stands for stem cells from human exfoliated deciduous teeth), from apical papilla (SCAP), and periodontal ligaments (PDLSCs).

Ideally, teeth for hDPSCs harvesting should still be vital, healthy, and have enough dental pulp. Deciduous teeth with at least two-thirds of their roots, third molars, fractured teeth, supernumerary teeth, and permanent teeth extracted for orthodontic indications are all candidates for stem cell recovery (Fig. 1).

01 A: The structure and the composition of a human tooth. The odontoblast borders the dental pulp beneath the dentin, with odontoblast processes projecting toward the enamel. B: Diverse cell populations are found in dental pulp, such as DPSCs, which can give rise to odontoblasts.

For this purpose, following informed consent, the dental surgeon examines the tooth, ruling out infections in the area. Under sterile conditions, prophylactic antibiotic therapy, and antiseptic mouthwash, the tooth is carefully extracted, avoiding breaking the crown and immediately transferring into the container. The collection of hDPSCs for long-term storage or banking for future therapeutic use is performed by specialized dentists and stem cell storage companies providing a comprehensive service to cryopreserve the stem cells for future clinical applications (Fig. 2).

02 Schematic representation of critical steps from tooth selection to DPSC cryopreservation and final application for therapeutic use (tissue engineering and regenerative medicine) and/or basic research (in vitro and in vivo studies).

hDPSCs can be differentiated into multiple cell types, such as osteoblasts and chondrocytes. Extracted third molar teeth (wisdom teeth) can serve as an ideal source of MSCs for tissue engineering. Consequently, harvested hDPSCs can later be used for potentially treating bone and cartilage injuries.

Studies have shown the potential of DPSCs implantation for chondral tissue surgical repair. Fernandes et al1 described a novel treatment for cartilage defects using scaffolds loaded with DPSCs in a large-animal (Brazilian miniature pig) model. The animals tolerated the procedure well, without any clinical or histological rejection of the DPSCs.

Also, cartilage healing was observed on macroscopic evaluation six weeks after treatment. Similarly, microscopic findings have confirmed a thicker deep layer with increased fibroblastic tissue on the superficial layer of the cartilage defect. In a preliminary study involving a rabbit model of cartilage damage, Mata et al2 analyzed the histological appearance of collagen fibers in animals that had been treated with the implantation of alginate only as compared with that in animals that had been treated with the implantation of alginate and chondrocytes or hDPSCs. The investigators observed poor regeneration with loss of cartilage tissue in the animals that had received alginate only than those that had also received autologous chondrocytes or hDPSCs. They also observed a smoother articular surface when hDPSCs were used instead of primary chondrocytes.

Recent reports have shown that hDPSCs suppress osteoarthritic macrophages mainly by secreting soluble factors, such as hepatocyte growth factor and transforming growth factor beta-1. The literature has shown that a single dose of locally administered hDPSCs significantly improves tissue regeneration. Li et al3 found that the intraarticular injection of hDPSCs had a suppressive effect on osteoarthritic macrophages in vitro and in vivo, alleviating cartilaginous damage in a rabbit knee osteoarthritis model. Similarly, in an experimental study involving an induced knee osteoarthritis model in rats, the injection of hDPSCs demonstrated positive effects in terms of restoring structural and morphological features, such as cellular hypertrophy and increased thickness of the joint cartilage, without an observed decrease in the number of chondrocytes. Moreover, local and systemic injections of hDPSCs in rats with progressive temporomandibular joint arthritis demonstrated therapeutic effects by inhibiting the expression of matrix metalloproteinases participating in bone and cartilage remodeling.

Reconstruction of bone defects represents a significant challenge in orthopaedic surgery. Several studies (including both animal models and human clinical trials) have investigated the use of hDPSCs with or without different types of scaffolds to repair cranial, maxilla, and mandible bone defects. In particular, a rabbit experimental study conducted by Feng et al4 suggested that gene therapy using Runt-related transcription factor 2 (Runx2)-modified hDPSCs was more effective during new bone formation in rapid distraction osteogenesis of the tibia when 1 ml of DPSCs suspension was injected directly into the distraction gap. In that study, the histological appearance of the lengthened segment showed newly formed mature and trabecular bone with complete bony continuity in the distraction gap, confirmed with high-resolution 3D micro-computed tomography images.

Human Dental Pulp Stem Cells: Do They Hold Potential for Orthopaedics?

Osteonecrosis is a degenerative bone disease characterized by the death of bone marrow and trabecular bone due to an interruption of the subchondral blood supply. Advanced disease ultimately can lead to the destruction of the joint involved. Therefore, early diagnosis increases the chances of treatment success. Clinically, the most frequently proposed treatment modalities of aseptic osteonecrosis of the femoral head include core decompression with various variants, nonvascularized and vascularized bone grafts, intertrochanteric and rotational bone grafts, and intertrochanteric transtrochanteric osteotomies.

MSCs administration is a novel strategy for treating bone and joint-related diseases. Feitosa et al5, in an experimental study, evaluated bone tissue recovery following the transplantation of hDPSCs in ovines with osteonecrosis of the femoral head induced by ethanol intra-bone injections. The investigators found that bone regeneration was faster in animals treated with core decompression and hDPSCs injections than in animals treated with core decompression alone. Also, the histological results showed good bone tissue recovery in animals treated with core decompression and hDPSCs injections. Similar results have been reported in pig and rat models using bone marrow- and adipose tissue-derived stem cells, respectively. [references] However, no studies have been conducted to compare outcomes between these stem cell sources.

Last, the main disadvantage of hDPSCs resides in their limited number of primary cells available in the dental pulp tissue compared to bone marrow and fat, yet cultured with promising growth rates. Additionally, its use demands carefully planned isolation and preservation from childhood and early adulthood before disease onset.

Conclusion

Tissue engineering continues to attract increasing attention as a promising treatment for various disorders, including cartilage defects, osteoarthritis, bone defects, and hip osteonecrosis. The success of tissue engineering relies on three factors: (1) seed cells, (2) biomaterials (scaffolds), and (3) bioactive molecules. MSCs are an attractive donor cell type for tissue engineering because their properties (selfrenewal, multipotency, immunomodulatory properties, and limited or no adverse effects) make them a safe and effective therapeutic tool for regenerative medicine. hDPSCs are easily accessible and exhibit higher proliferative capacities than bone marrow-derived MSCs. These characteristics render hDPSCs suitable cell candidates for cell-based therapies and tissue engineering in orthopaedics

References

1. Fernandes TL, Shimomura K, Asperti A, Pinheiro CCG, Caetano HVA, Oliveira CRGCM, Nakamura N, Hernandez AJ, Bueno DF. Development of a Novel Large Animal Model to Evaluate Human Dental Pulp Stem Cells for Articular Cartilage Treatment. Stem Cell Rev Rep. 2018 Oct;14(5):734-743. doi: 10.1007/s12015-018-9820-2. PMID: 29728886; PMCID: PMC6132738.
2. Mata M, Milian L, Oliver M, Zurriaga J, Sancho-Tello M, de Llano JJM, Carda C. In Vivo Articular Cartilage Regeneration Using Human Dental Pulp Stem Cells Cultured in an Alginate Scaffold: A Preliminary Study. Stem Cells Int. 2017;2017:8309256. doi: 10.1155/2017/8309256. Epub 2017 Aug 16. PMID: 28951745; PMCID: PMC5603743.
3. Li PL, Wang YX, Zhao ZD, Li ZL, Liang JW, Wang Q, Yin BF, Hao RC, Han MY, Ding L, Wu CT, Zhu H. Clinical-grade human dental pulp stem cells suppressed the activation of osteoarthritic macrophages and attenuated cartilaginous damage in a rabbit osteoarthritis model. Stem Cell Res Ther. 2021 May 1;12(1):260. doi: 10.1186/s13287-021-02353-2. PMID: 33933140; PMCID: PMC8088312.
4. Feng G, Zhang J, Feng X, Wu S, Huang D, Hu J, Zhu S, Song D. Runx2 modified dental pulp stem cells (DPSCs) enhance new bone formation during rapid distraction osteogenesis (DO). Differentiation. 2016 Oct- Nov;92(4):195-203. doi: 10.1016/j.diff.2016.06.001. Epub 2016 Jun 14. PMID: 27313006.
5. Feitosa ML, Fadel L, Beltrão-Braga PC, Wenceslau CV, Kerkis I, Kerkis A, Birgel Júnior EH, Martins JF, Martins Ddos S, Miglino MA, Ambrósio CE. Successful transplant of mesenchymal stem cells in induced osteonecrosis of the ovine femoral head: preliminary results. Acta Cir Bras. 2010 Oct;25(5):416-22. doi: 10.1590/ s0102-86502010000500006. PMID: 20877951.