N-Acetyl-Cysteine-Loaded Biomimetic Nanofibrous Scaffold for Osteogenesis of Induced-Pluripotent-Stem-Cell-Derived Mesenchymal Stem Cells and Bone Regeneration

Stem Cells in Bone Tissue Engineering: Progress, Promises and Challenges

Bone defects from accidents, congenital conditions, and age-related diseases significantly impact quality of life. Recent advancements in bone tissue engineering (TE) involve biomaterial scaffolds, patient-derived cells, and bioactive agents, enabling functional bone regeneration. Stem cells, obtained from numerous sources including umbilical cord blood, adipose tissue, bone marrow, and dental pulp, hold immense potential in bone TE. Induced pluripotent stem cells and genetically modified stem cells can also be used. Proper manipulation of physical, chemical, and biological stimulation is crucial for their proliferation, maintenance, and differentiation. Stem cells contribute to osteogenesis, osteoinduction, angiogenesis, and mineralization, essential for bone regeneration. This review provides an overview of the latest developments in stem cell-based TE for repairing and regenerating defective bones.

The role of N-acetylcysteine in osteogenic microenvironment for bone tissue engineering

Bone defect is a common clinical symptom which can arise from various causes. Currently, bone tissue engineering has demonstrated positive therapeutic effects for bone defect repair by using seeding cells such as mesenchymal stem cells and precursor cells. N-acetylcysteine (NAC) is a stable, safe and highly bioavailable antioxidant that shows promising prospects in bone tissue engineering due to the ability to attenuate oxidative stress and enhance the osteogenic potential and immune regulatory function of cells. This review systematically introduces the antioxidant mechanism of NAC, analyzes the advancements in NAC-related research involving mesenchymal stem cells, precursor cells, innate immune cells and animal models, discusses its function using the classic oral microenvironment as an example, and places particular emphasis on the innovative applications of NAC-modified tissue engineering biomaterials. Finally, current limitations and future prospects are proposed, with the aim of providing inspiration for targeted readers in the field.

3D printing of reduced glutathione grafted gelatine methacrylate hydrogel scaffold promotes diabetic bone regeneration by activating PI3K/Akt signaling pathway

Diabetic individuals are frequently associated with increased fracture risk and poor bone healing capacity, and the treatment of diabetic bone defects remains a great challenge in orthopedics. In this study, an antioxidant hydrogel was developed using reduced glutathione grafted gelatine methacrylate (GelMA-g-GSH), followed by 3D printing to form a tissue engineering scaffold, which possessed appropriate mechanical property and good biocompatibility. In vitro studies displayed that benefitting from the sustained delivery of reduced glutathione, GelMA-g-GSH scaffold enabled to suppress the overproduction of reactive oxygen species (ROS) and reduce the oxidative stress of cells. Osteogenic experiments showed that GelMA-g-GSH scaffold exhibited excellent osteogenesis performance, with the elevated expression levels of osteogenesis-related genes and proteins. Further, RNA-sequencing revealed that activation of PI3K/Akt signaling pathway of MC3T3-E1 seeded on GelMA-g-GSH scaffold may be the underlying mechanism in promoting osteogenesis. In vivo, diabetic mice calvarial defects experiment demonstrated enhanced bone regeneration after the implantation of GelMA-g-GSH scaffold, as shown by micro-CT and histological analysis. In summary, 3D-printed GelMA-g-GSH scaffold can not only scavenge ROS, but also promote proliferation and differentiation of osteoblasts by activating PI3K/Akt signaling pathway, thereby accelerating bone repair under diabetes.

Immunomodulatory effects of N-acetyl cysteine treated SCAP

INTRODUCTION

Stem cells of the apical papilla (SCAP) play an important role in regenerative endodontic procedures (REPs). Previous studies have shown that during REPs, bacteria can activate the innate immune system and cause indirect stem cell toxicity, leading to the lysis of SCAP. N-acetylcysteine (NAC) treated cells are resistant to apoptosis and have increased differentiation capabilities. The immunomodulatory properties of NAC treated SCAP are still unknown. Hence, the aim of this study is to evaluate the interactions of SCAP pre-treated with and without NAC with the immune system.

METHODS

Flow cytometric analysis was performed to assess the effects of NAC on SCAP viability. Human SCAP were then cultured and were either pre-treated with NAC or non-treated and co-cultured with human Peripheral blood mononuclear cells (PBMCs). A lactate dehydrogenase assay was performed to evaluate the levels of immune cell mediated apoptosis followed by an enzyme-linked immunosorbent assay (ELISA) to measure levels of pro-inflammatory cytokines for these co-cultures. Data were analyzed using an ANOVA with a post-hoc Tukey test.

RESULTS

Cells treated with NAC had similar levels of viability as the controls. SCAP pre-treated with NAC had a significantly lower immune cell-mediated cytotoxicity to non-activated and activated PBMCs. The ELISA results showed that SCAP pre-treated with NAC induced lower levels of proinflammatory cytokines.

CONCLUSIONS

SCAP pre-treated with NAC have a higher chance of surviving the activated immune system. This information may provide a better insight into the properties of these stem cells and may be the key to making REPs more predictable.

Anisotropic silk nanofiber layers as regulators of angiogenesis for optimized bone regeneration

Osteogenesis-angiogenesis coupling processes play a crucial role in bone regeneration. Here, electric field induced aligned nanofiber layers with tunable thickness were coated on the surface of pore walls inside the deferoxamine (DFO)-laden silk fibroin (SF) and hydroxyapatite (HA) composite scaffolds to regulate the release of DFO to control vascularization dynamically. Longer electric field treatments resulted in gradually thickening layers to reduce the release rate of DFO where the released amount of DFO decreased gradually from 84% to 63% after 28 days. Besides the osteogenic capacity of HA, the changeable release of DFO brought different angiogenic behaviors in bone regeneration process, which provided a desirable niche with osteogenic and angiogenic cues. Anisotropic cues were introduced to facilitate cell migration inside the scaffolds. Changeable cytokine secretion from endothelial cells cultured in the different scaffolds revealed the regulation of cell responses related to vascularization in vitro. Peak expression of angiogenic factors appeared at days 7, 21 and 35 for endothelial cells cultured in the scaffolds with different silk nanofier layers, suggesting the dynamical regulation of angiogenesis. Although all of the scaffolds had the same silk and HA composition, in vitro cell studies indicated different osteogenic capacities for the scaffolds, suggesting that the regulation of DFO release also influenced osteogenesis outcomes in vitro. In vivo, the best bone regeneration occurred in defects treated with the composite scaffolds that exhibited the best osteogenic capacity in vitro. Using a rat bone defect model, healing was achieved within 12 weeks, superior to those treated with previous SF-HA composite matrices. Controlling angiogenic properties of bone biomaterials dynamically is an effective strategy to improve bone regeneration capacity.

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Anisotropic silk nanofiber layers with tunable thickness control the sustained release of DFO dynamically.

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Dynamical regulation of angiogenesis was achieved in bone regeneration process through tuning the release behaviors of DFO.

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Significantly improved bone regeneration through the synergistic effect of optimal vascularization and osteogenesis.