Regenerative Characteristics of Apical Papilla-derived Cells from Immature Teeth with Pulpal and Periapical Pathosis

The potential use of ascorbic acid to recover the cellular senescence of lipopolysaccharide-induced human apical papilla cells: an in vitro study

OBJECTIVES

To examine the effect of lipopolysaccharide (LPS) on cellular senescence induction of human apical papilla cells (hAPCs) and evaluate the potential use of 50 μg/ml ascorbic acid to recover cellular senescence and regenerative functions.

MATERIALS AND METHODS

hAPCs were treated with LPS at 1 and 10 μg/ml either with or without 50 μg/ml ascorbic acid for 48 h. The cellular senescence biomarkers were analyzed by senescence-associated β-galactosidase (SA-β-gal) staining and senescence-related gene expression, p16 and p21. Cell migration, at 12 h and 24 h, was evaluated using a scratch wound assay. Mineralization potential was assessed at 21 days using Alizarin red S staining and dentine sialophosphoprotein (DSPP) and bone sialoprotein (BSP) gene expression.

RESULTS

1 μg/ml and 10 μg/ml LPS stimulation for 48 h induced cellular senescence, as shown by remarkable SA-β-gal staining and p16 and p21 gene expression. The percentage of wound closure and mineralized formation was reduced. The co-incubation with ascorbic acid significantly down-regulated the level of SA-β-gal staining. The reduction of senescence-associated gene expressions was observed. Ascorbic acid improved cell migration, mineralized nodule formation, and the expression of DSPP and BSP genes in LPS-treated hAPCs.

CONCLUSIONS

LPS significantly promoted cellular senescence on hAPCs and diminished the cell function capacity. Co-presence of ascorbic acid could impede cellular senescence and possibly improve the regenerative capacity of LPS-induced senescent hAPCs in vitro.

CLINICAL RELEVANCE

The data support the in vitro potential benefit of ascorbic acid on cellular senescence recovery of apical papilla cells.

3D Organoids for Regenerative Endodontics

Apical periodontitis is the inflammation and destruction of periradicular tissues, mediated by microbial factors originating from the infected pulp space. This bacteria-mediated inflammatory disease is known to interfere with root development in immature permanent teeth. Current research on interventions in immature teeth has been dedicated to facilitating the continuation of root development as well as regenerating the dentin-pulp complex, but the fundamental knowledge on the cellular interactions and the role of periapical mediators in apical periodontitis in immature roots that govern the disease process and post-treatment healing is limited. The limitations in 2D monolayer cell culture have a substantial role in the existing limitations of understanding cell-to-cell interactions in the pulpal and periapical tissues. Three-dimensional (3D) tissue constructs with two or more different cell populations are a better physiological representation of in vivo environment. These systems allow the high-throughput testing of multi-cell interactions and can be applied to study the interactions between stem cells and immune cells, including the role of mediators/cytokines in simulated environments. Well-designed 3D models are critical for understanding cellular functions and interactions in disease and healing processes for future therapeutic optimization in regenerative endodontics. This narrative review covers the fundamentals of (1) the disease process of apical periodontitis; (2) the influence and challenges of regeneration in immature roots; (3) the introduction of and crosstalk between mesenchymal stem cells and macrophages; (4) 3D cell culture techniques and their applications for studying cellular interactions in the pulpal and periapical tissues; (5) current investigations on cellular interactions in regenerative endodontics; and, lastly, (6) the dental-pulp organoid developed for regenerative endodontics.

Pediatric Overweight, Fatness and Risk for Dyslipidemia Are Related to Diet: A Cross-Sectional Study in 9-year-old Children

Pediatric overweight, dyslipidemia and insulin resistance can result from unhealthy lifestyle habits and increase morbidity and mortality in adulthood. Herein, we evaluated the relationship between diet and physical activity patterns with the metabolic health of 9-year-old school children. Measurements included anthropometry, adiposity, lipid, and glycemic profiles. Questionnaires evaluated diet and physical activity. Exploratory factor analysis (EFA) screened for diet patterns, and multilevel models evaluated diet and physical activity patterns against overweight, dyslipidemia, and insulin resistance markers across schools and children. EFA highlighted two diet patterns, Western and Traditional. Food rich in fat, salt, and sugar and fewer vegetables and fruits defined the Western pattern. The Traditional pattern, linked to healthier eating habits, had analogies to the Mediterranean diet. Overall, 39% of the children were overweight (including the obese), while 62% presented cardiovascular risk factors on their lipid profiles. Normal-weight children presented 60% high cholesterol incidence. Global insulin resistance incidence was 4.1%, but almost doubled among the overweight/obese. The Westernized diet consistently linked to worse cardiovascular risk markers, even independently of physical practice. Intensive or competitive physical activity was associated with decreased triglycerides (p = 0.003), regardless of diet. Future prospective studies are warranted to validate these results externally.

Protective Actions in Apical Periodontitis: The Regenerative Bioactivities Led by Mesenchymal Stem Cells

Resulting from bacterial infection, apical periodontitis (AP) is a common inflammatory disease of the periapical region of the tooth. The regeneration of the destroyed periapical alveolar bone and the surrounding periodontium tissues has long been a difficult task in clinical practice. These lesions are closely related to pathogen invasion and an overreactive immune response. It is worth noting that the protective healing process occurs simultaneously, in which mesenchymal stem cells (MSCs) have a crucial function in mediating the immune system and promoting regeneration. Here, we review the recent studies related to AP, with a focus on the regulatory network of MSCs. We also discuss the potential therapeutic approaches of MSCs in inflammatory diseases to provide a basis for promoting tissue regeneration and modulating inflammation in AP. A deeper understanding of the protective action of MSCs and the regulatory networks will help to delineate the underlying mechanisms of AP and pave the way for stem-cell-based regenerative medicine in the future.

Engineering a novel stem cells from apical papilla - macrophages organoid for regenerative endodontics

INTRODUCTION

Three-dimension (3D) tissue-construct with a heterogeneous cell population is critical to understand the interactions between immune cells and stem cells from apical papilla (SCAP) in the periapical region for developing treatment strategies in regenerative endodontics. This study aims to develop and characterize a 3D tissue-construct with binary cell system for studying the interactions between SCAP and macrophages in presence of lipopolysaccharide (LPS - pro-inflammatory) and interleukin-4 (IL-4 - anti-inflammatory) environments.

METHODS

SCAP and macrophages were seeded in the 3D printed dumbbell-shaped molds to generate tissue-constructs with binary cell population. Two experimental (LPS and IL-4) and control (non-stimulation) conditions were applied to the tissue-constructs to determine the characteristics of the tissue-construct, volume of viable cells and their morphology using a confocal laser scanning microscopy from 0 to 7 days period. Experiments were conducted in triplicates and data were analyzed with trend analysis and two-way analysis of variance at the significance of p < 0.05.

RESULTS

The tissue-constructs revealed distinct SCAP-macrophage interaction in pro-/anti-inflammatory environments. SCAP displayed characteristic self-organization as a cap-shaped structure in the tissue-construct. The growth of cells and cell-to-cell as well as cell-to-matrix interactions resulted in 70% and 30% decreased dimension of the tissue graft on the SCAP side and macrophage side respectively at day 7 (p < 0.0001). The tissue environments influenced macrophages-SCAP interactions, resulting in altered viable cell volume (p < 0.05), morphology and structural organization.

CONCLUSIONS

This study developed and characterized an apical papilla organoid in a 3D collagen based tissue-construct for studying SCAP-macrophage crosstalk in tissue regeneration as well as repair.

In vitro evaluation of periapical lesion-derived stem cells for dental pulp tissue engineering

Dental pulp tissue engineering is a promising alternative treatment for pulpitis and periapical periodontitis, and dental pulp stem cells (DPSCs) are considered to be the gold standard for dental seed cell research. Periapical lesions harbor mesenchymal stem cells with the capacity for self-renewal and multilineage differentiation. However, it remains unknown whether these periapical lesion-derived stem cells (PLDSCs) are suitable for dental pulp tissue engineering. To investigate this possibility, PLDSCs and DPSCs were isolated using the tissue outgrowth method and cultured under identical conditions. We then performed in vitro experiments to investigate their biological characteristics. Our results indicate that PLDSCs proliferate actively in vitro and exhibit similar morphology, immunophenotype and multilineage differentiation ability as DPSCs. Simultaneously, PLDSCs exhibit stronger migrative ability and express more vascular endothelial growth factor and glial cell line-derived neurotrophic factor than DPSCs, and PLDSC-derived conditioned medium was more effective in tube formation assay. The mRNA expression levels of immunomodulatory genes HLA-G, IDO and ICAM-1 were also higher in PLDSCs. However, regarding osteo/odontogenic differentiation, PLDSCs showed weaker alkaline phosphatase staining and lower calcified nodule formation compared to DPSCs, as well as lower expression of ALP, RUNX2 and DSPP, as confirmed by a quantitative RT-PCR. The osteo/odontogenic protein expression levels of DSPP, RUNX2, DMP1 and SP7 were also higher in DPSCs. The present study demonstrates that PLDSCs demonstrate potential use as seed cells for dental pulp regeneration, especially for achieving enhanced neurovascularization.

Stem Cell-based Dental Pulp Regeneration: Insights From Signaling Pathways

Deep caries, trauma, and severe periodontitis result in pulpitis, pulp necrosis, and eventually pulp loss. However, no clinical therapy can regenerate lost pulp. A novel pulp regeneration strategy for clinical application is urgently needed. Signaling transduction plays an essential role in regulating the regenerative potentials of dental stem cells. Cytokines or growth factors, such as stromal cell-derived factor (SDF), fibroblast growth factor (FGF), bone morphogenetic protein (BMP), vascular endothelial growth factor (VEGF), WNT, can promote the migration, proliferation, odontogenic differentiation, pro-angiogenesis, and pro-neurogenesis potentials of dental stem cells respectively. Using the methods of signaling modulation including growth factors delivery, genetic modification, and physical stimulation has been applied in multiple preclinical studies of pulp regeneration based on cell transplantation or cell homing. Transplanting dental stem cells and growth factors encapsulated into scaffold regenerated vascularized pulp-like tissue in the root canal. Also, injecting a flowable scaffold only with chemokines recruited endogenous stem/progenitor cells for pulp regeneration. Notably, dental pulp regeneration has gradually developed into the clinical phase. These findings enlightened us on a novel strategy for structural and functional pulp regeneration through elaborate modulation of signaling transduction spatially and temporally via clinically applicable growth factors delivery. But challenges, such as the adverse effects of unphysiological signaling activation, the controlled drug release system, and the safety of gene modulation, are necessary to be tested in future works for promoting the clinical translation of pulp regeneration.

Impact of remnant healthy pulp and apical tissue on outcomes after simulated regenerative endodontic procedure in rat molars

When regenerative endodontic procedures (REPs) are performed on immature teeth diagnosed with pulp necrosis and apical periodontitis, various healing patterns occur. Furthermore, infected immature teeth with endodontic disorders often exhibit some remnant pulp and apical tissue. Therefore, this study investigated the impact of remnant healthy or fully functional pulp and apical tissue on healing patterns after REPs. Simulated REPs were performed on non-infected immature rat molars with different amounts of remnant pulp and apical tissue. Healing patterns in these teeth were assessed after 28 days. Teeth with 0.81–0.91 mm of remnant pulp healed with pulp-like tissue, dentin, and osteodentin-like dentin-associated mineralized tissue (OSD-DAMT); teeth with 0.60–0.63 mm of remnant pulp healed with pulp-like tissue and OSD-DAMT; teeth with 0.13–0.43 mm of remnant pulp healed with periodontal ligament (PDL)-like tissue, OSD-DAMT, and cementum-like dentin-associated mineralized tissue (CEM-DAMT); and teeth with disorganization of pulp and apical tissues at 0.15–0.38 mm beyond the root apex healed with PDL-like tissue, CEM-DAMT, and intracanal bone (IB). Loss of Hertwig’s epithelial root sheath was observed with IB formation. These results showed that four distinct healing patterns occurred after REPs, depending on the preoperative amount of remnant healthy pulp and apical tissue.

Mineral trioxide aggregate apexification: a 20-year case review

Apexification strategies in traumatised non-vital immature permanent teeth can promote root-end closure and continued root development. However, traumatic injuries may compromise the integrity of generative cells of the apical papilla responsible for root maturation. This report describes the long-term treatment outcome of mineral trioxide aggregate (MTA) apexification managed with late-term surgical intervention. A seven-year-old male reported with swelling and suppuration associated with a traumatised maxillary left central incisor (#21). After palliative treatment and MTA apexification procedures, the incisor demonstrated normal function during a 14.5-year period with radiographic evidence of atypical radicular elongation. Seventeen years after initial treatment, the patient presented with mid-plate buccal swelling and surgical treatment was completed involving root resection, biopsy of a spherical mineralised tissue specimen and placement of MTA root-end filling. Periapical healing and normal tooth function was evident at the 20-year review.

[Effects of tumor necrosis factor-α on osteogenic differentiation and Notch signaling pathway in human periodontal ligament stem cells]

OBJECTIVE

To evaluate the effects of tumor necrosis factor-α (TNF-α) on osteogenic differentiation and Notch signaling pathway of periodontal ligament stem cells (PDLSCs) and to investigate the regulatory role of Notch signaling pathway on the osteogenic differentiation of PDLSCs under the influence of TNF-α.

METHODS

PDLSCs were obtained through enzyme digestion and tissue block method. The expression levels of stem cell surface markers CD105, CD90, CD146, CD45, and CD31 were detected by fluorescence activated cell sorter (FACS). PDLSCs were divided into experimental (10 ng·mL⁻¹ TNF-α) and control groups (0 ng·mL⁻¹ TNF-α). The proliferation ability of PDLSCs was detected using cell counting kit-8 (CCK-8). The effect of TNF-α on the osteogenic ability of PDLSCs were tested by measuring alkaline phosphatase (ALP) activity and conducting alizarin red staining and quantitative real-time polymerase chain reaction (PCR). We tested Notch signal pathway receptors Notch1, Notch2, ligand JAG1, JGA2, and downstream gene Hes-1. Changes in DLL1 expression were detected by quantitative real-time PCR.

RESULTS

FACS profiling showed that PDLSCs were strongly positive for CD105, CD90, and CD146 but negative for CD45 and CD31. CCK-8 results showed that TNF-α could promote the proliferation of PDLSCs (P<0.05). ALP activity in the experimental group was lower than that in the control group (P<0.05). Alizarin red staining showed that the experimental group had decreased mineralized nodules as compared with the control group. Quantitative real-time PCR results showed that the mRNA expression of osteogenic marker genes cementum attachment protein (CAP), osteopontin (OPN), and Runt-related transcription factor 2 (Runx2) significantly decreased in the experimental group as compared with those in the control group (P<0.05). The expression levels of Notch1, Notch2, JAG1, JGA2 and Hes-1 were significantly decreased (P<0.05), whereas those of Notch3 and DLL1 were increased in Notch signaling pathway-related molecules (P<0.05).

CONCLUSIONS

TNF-α can promote PDLSCs proliferation and inhibit bone differentiation and Notch signaling pathway expression, indicating that the Notch signaling pathway regulates PDLSCs osteogenic differentiation.

Stem Cells From the Apical Papilla (SCAP) as a Tool for Endogenous Tissue Regeneration

Stem cells extracted from developing tissues possibly exhibit not only unique but also superior traits against their developed counterparts. Indeed, stem cells from the apical papilla (SCAP); a unique group of dental stem cells related to developing roots have been shown to be a promising tool for regenerative endodontic procedures and regeneration in general. Studies have characterized the phenotypic traits as well as other regenerative potentials of these cells. Specific sub-populations have been highlighted as well as their neurogenic and angiogenic properties. Nevertheless, in light of the previously discussed features and potential applications of SCAP, there is still much to understand and a lot of information to unravel. The current review will discuss the role of specific markers for detection of different functional populations of SCAP; including CD146 and STRO-1, as well as their true multilineage differentiation potential. In particular, the role of the secretome in association with paracrine signaling in inflammatory microenvironments is also tackled. Additionally, the role of SCAP both in vitro and in vivo during regenerative approaches and in response to different growth factors and biologic scaffolds is highlighted. Finally, this review will shed light on current knowledge regarding the clinical translational potential of SCAP and elucidate possible areas for future research applications.