Interests of Exosomes in Bone and Periodontal Regeneration: A Systematic Review

Microbial- and host immune cell-derived extracellular vesicles in the pathogenesis and therapy of periodontitis: A narrative review

Periodontitis is a chronic inflammatory disease caused by dysbiotic biofilms and destructive host immune responses. Extracellular vesicles (EVs) are circulating nanoparticles released by microbes and host cells involved in cell-to-cell communication, found in body biofluids, such as saliva and gingival crevicular fluid (GCF). EVs are mainly involved in cell-to-cell communication, and may hold promise for diagnostic and therapeutic purposes. Periodontal research has examined the potential involvement of bacterial- and host-cell-derived EVs in disease pathogenesis, diagnosis, and therapy, but data remains scarce on immune cell- or microbial-derived EVs. In this narrative review, we first provide an overview of the role of microbial and host-derived EVs on disease pathogenesis. Recent studies reveal that Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans-derived outer membrane vesicles (OMVs) can activate inflammatory cytokine release in host cells, while M1 macrophage EVs may contribute to bone loss. Additionally, we summarised current in vitro and pre-clinical research on the utilisation of immune cell and microbial-derived EVs as potential therapeutic tools in the context of periodontal treatment. Studies indicate that EVs from M2 macrophages and dendritic cells promote bone regeneration in animal models. While bacterial EVs remain underexplored for periodontal therapy, preliminary research suggests that P. gingivalis OMVs hold promise as vaccine candidates. Finally, we acknowledge the current limitations present in the field of translating immune cell derived EVs and microbial derived EVs in periodontology. It is concluded that microbial and host immune cell-derived EVs have a role in periodontitis pathogenesis and hence may be useful for studying disease pathophysiology, and as diagnostic and treatment monitoring biomarkers.

Exosomal circ_0000722 derived from periodontal ligament stem cells undergoing osteogenic differentiation promotes osteoclastogenesis

Periodontal ligament stem cells (PDLSCs), which are considered promising stem cells for regeneration of periodontal bony tissue, can also manipulate alveolar bone remodeling by exosomes. In this study, we investigated interactions between PDLSCs under osteogenic differentiation and osteoclast precursors. The results showed that conditioned medium from PDLSCs under 5d osteogenic induction promoted osteoclastogenesis of RAW264.7 cells. The exosomes extracted from those conditioned media showed similar effects on osteoclastogenesis. Furthermore, exosomes from PDLSCs under 5d of osteogenic induction showed significantly high expression of circ_0000722, compared with exosomes from PDLSCs before osteogenic induction. Downregulation of circ_0000722 significantly attenuated the effect of PDLSC-derived exosomes on the osteoclastogenesis of RAW264.7 cells. Our findings suggested that exosomal circ_0000722 derived from periodontal ligament stem cells undergoing osteogenic differentiation might promote osteoclastogenesis by upregulating TRAF6 expression and activating downstream NF-κB and AKT signaling pathways.

Effects of periodontal cells-derived extracellular vesicles on mesenchymal stromal cell function

OBJECTIVE

To enrich and compare three extracellular vesicles-EV subtypes (apoptotic bodies, microvesicles and small EV) from three periodontal cells (periodontal ligament cells-PDLCs, alveolar bone-derived osteoblasts-OBs and gingival fibroblasts-GFs), and assess uptake and cell function changes in buccal fat pad-derived mesenchymal stromal cells (BFP-MSCs).

BACKGROUND

Periodontal cells such as PDLCs, OBs and GFs have the potential to enhance bone and periodontal regeneration, but face significant challenges, such as the regulatory and cost implications of in vitro cell culture and storage. To address these challenges, it is important to explore alternative 'cell-free' strategies, such as extracellular vesicles which have emerged as promising tools in regenerative medicine, to facilitate osteogenic differentiation and bone regeneration.

METHODS AND MATERIALS

Serial centrifuges at 2600 and 16 000 g were used to isolate apoptotic bodies and microvesicles respectively. Small EV-sEV was enriched by our in-house size exclusion chromatography (SEC). The cellular uptake, proliferation, migration and osteogenic/adipogenic differentiation genes were analysed after EVs uptake in BFP-MSCs.

RESULTS

Three EV subtypes were enriched and characterised by morphology, particle size and EV-associated protein expression-CD9. Cellular uptake of the three EVs subtypes was observed in BFP-MSCs for up to 7 days. sEV from the three periodontal cells promoted proliferation, migration and osteogenic gene expression. hOBs-sEV showed superior levels of osteogenesis markers compared to that hPDLCs-sEV and hGFs-sEV, while hOBs-16k EV promoted adipogenic gene expression compared to that from hPDLCs and hGFs.

CONCLUSIONS

Our proof-of-concept data demonstrate that hOBs-sEV might be an alternative cell-free therapeutic for bone tissue engineering.

Research Progress of Polydopamine Hydrogel in the Prevention and Treatment of Oral Diseases

Oral diseases represent one of the most prevalent diseases globally and are associated with serious health and economic burdens, greatly altering the quality of life of affected individuals. Various biomaterials play important roles in the treatment of oral diseases. To some extent, the development of biomaterials has promoted progress in clinically available oral medicines. Hydrogels have unique tunable advantages that make them useful in the next generation of regenerative strategies and have been widely applied in both oral soft and hard tissues repair. However, most hydrogels lack self-adhesive properties, which may result in low repair efficacy. Polydopamine (PDA), the primary adhesive component, has attracted increasing attention in recent years. PDA-modified hydrogels exhibit reliable and suitable adherence to tissues and easily integrate into tissues to promote repair efficiency. This paper reviews the latest research progress on PDA hydrogels and elaborates on the mechanism of the reaction between PDA functional groups and hydrogels, and summarizes the biological properties and the applications of PDA hydrogels in the prevention and treatment of the field of oral diseases. It is also proposed that in future research we should simulate the complex microenvironment of the oral cavity as much as possible, coordinate and plan various biological events rationally, and realize the translation from scientific research to clinical practice.

Roles of exosomes in regenerative periodontology: a narrative review

Periodontitis is the primary cause of irreversible destruction of the periodontium surrounding teeth. Proinflammatory cytokines are secreted by pathogens in the biofilm and destroy the periodontium. Exosomes released into all biological fluids from saliva have enabled many innovations in the early diagnosis and treatment of periodontal diseases. This narrative review describes the role of exosomes in various diseases, and their involvement in periodontal diseases and periodontal regeneration primarily. Since guided tissue regeneration offers unpredictable results that vary according to the case, new developments in periodontal treatment are needed. Exosomes are suitable drug carriers for periodontal regeneration due to their isolation from every biological fluid, biocompatibility, low toxicity and high concentration of drugs reaching the target tissue. Exosomes obtained from mesenchymal stem cells can be used for periodontal regeneration in periodontal flaps, scaffolds, or periodontal defect areas through biomaterials such as drugs and hydrogels. Exosomes are significant in the early diagnosis and development of treatment of many diseases such as cardiovascular, neurodegenerative, diabetes and prognostic markers in cancer. Future studies are needed to elucidate the effects and possible mechanisms of exosomes in periodontitis and periodontal diseases and other systemic diseases, as they have many promises in diagnosis, treatment, and prognosis.

Novel approaches for periodontal tissue engineering

The periodontal complex involves the hard and soft tissues which support dentition, comprised of cementum, bone, and the periodontal ligament (PDL). Periodontitis, a prevalent infectious disease of the periodontium, threatens the integrity of these tissues and causes irreversible damage. Periodontal therapy aims to repair and ultimately regenerate these tissues toward preserving native dentition and improving the physiologic integration of dental implants. The PDL contains multipotent stem cells, which have a robust capacity to differentiate into various types of cells to form the PDL, cementum, and alveolar bone. Selection of appropriate growth factors and biomaterial matrices to facilitate periodontal regeneration are critical to recapitulate the physiologic organization and function of the periodontal complex. Herein, we discuss the current state of clinical periodontal regeneration including a review of FDA-approved growth factors. We will highlight advances in preclinical research toward identifying additional growth factors capable of robust repair and biomaterial matrices to augment regeneration similarly and synergistically, ultimately improving periodontal regeneration's predictability and long-term efficacy. This review should improve the readers' understanding of the molecular and cellular processes involving periodontal regeneration essential for designing comprehensive therapeutic approaches.

SHED‐derived exosomes improve the repair capacity and osteogenesis potential of hPDLCs

OBJECTIVE

Exosomes secreted by stem cells are recognized as a critical component in tissue regeneration during stem cell-based therapy. Considering the limited sources and bone regeneration efficiency of human periodontal ligament cells (hPDLCs), we explored whether exosomes secreted by stem cells from human exfoliated deciduous teeth (SHED-exo) could improve the pluripotency and regenerative potential of hPDLCs.

METHODS AND MATERIALS

In hPDLCs, cell proliferation, migration, cell cycle, apoptosis, and osteogenic differentiation were detected after cells were exposed to SHED-exo (SHED-exo group), blank (control group), or control supernatant without exo (Csup group), via CCK-8, scratch analysis, flow cytometric, real-time PCR, and so on. Exosomes sequencing was performed to compare and analyze miRNAs contented in SHED-exo and hPDLC-exo.

RESULTS

As compared to control or Csup, SHED-exo significantly increased migration, apoptosis, and proliferation, promoted cell cycle transition from G1 to S phase in hPDLCs, and enhanced Runx2 expression and mineralization. In addition, it may be explained by the significant differences in miRNA contented in SHED-exo and hPDLC-exo.

CONCLUSION

Exosomes from SHED can improve cell proliferation, migration, cell cycle, apoptosis, and osteogenic differentiation of hPDLCs, which highlights the therapeutic value of this bioactive component in the regeneration of periodontal tissues using hPDLCs in clinical practice.

Periodontal and Dental Pulp Cell-Derived Small Extracellular Vesicles: A Review of the Current Status

Extracellular vesicles (EVs) are membrane-bound lipid particles that are secreted by all cell types and function as cell-to-cell communicators through their cargos of protein, nucleic acid, lipids, and metabolites, which are derived from their parent cells. There is limited information on the isolation and the emerging therapeutic role of periodontal and dental pulp cell-derived small EVs (sEVs, <200 nm, or exosome). In this review, we discuss the biogenesis of three EV subtypes (sEVs, microvesicles and apoptotic bodies) and the emerging role of sEVs from periodontal ligament (stem) cells, gingival fibroblasts (or gingival mesenchymal stem cells) and dental pulp cells, and their therapeutic potential in vitro and in vivo. A review of the relevant methodology found that precipitation-based kits and ultracentrifugation are the two most common methods to isolate periodontal (dental pulp) cell sEVs. Periodontal (and pulp) cell sEVs range in size, from 40 nm to 2 μm, due to a lack of standardized isolation protocols. Nevertheless, our review found that these EVs possess anti-inflammatory, osteo/odontogenic, angiogenic and immunomodulatory functions in vitro and in vivo, via reported EV cargos of EV–miRNAs, EV–circRNAs, EV–mRNAs and EV–lncRNAs. This review highlights the considerable therapeutic potential of periodontal and dental pulp cell-derived sEVs in various regenerative applications.

Modulation of immune-inflammatory responses through surface modifications of biomaterials to promote bone healing and regeneration

Control of inflammation is indispensable for optimal oral wound healing and tissue regeneration. Several biomaterials have been used to enhance the regenerative outcomes; however, the biomaterial implantation can ensure an immune-inflammatory response. The interface between the cells and the biomaterial surface plays a critical role in determining the success of soft and hard tissue regeneration. The initial inflammatory response upon biomaterial implantation helps in tissue repair and regeneration, however, persistant inflammation impairs the wound healing response. The cells interact with the biomaterials through extracellular matrix proteins leading to protein adsorption followed by recruitment, attachment, migration, and proliferation of several immune-inflammatory cells. Physical nanotopography of biomaterials, such as surface proteins, roughness, and porosity, is crucial for driving cellular attachment and migration. Similarly, modification of scaffold surface chemistry by adapting hydrophilicity, surface charge, surface coatings, can down-regulate the initiation of pro-inflammatory cascades. Besides, functionalization of scaffold surfaces with active biological molecules can down-regulate pro-inflammatory and pro-resorptive mediators' release as well as actively up-regulate anti-inflammatory markers. This review encompasses various strategies for the optimization of physical, chemical, and biological properties of biomaterial and the underlying mechanisms to modulate the immune-inflammatory response, thereby, promoting the tissue integration and subsequent soft and hard tissue regeneration potential of the administered biomaterial.