Low-intensity pulsed ultrasound enhances immunomodulation and facilitates osteogenesis of human periodontal ligament stem cells by inhibiting the NF-κB pathway

Biomechanical force-primed periodontal ligament stem cells exhibit a tolerance effect against bacterial inflammation

OBJECTIVE

As mechanosensory cells, periodontal ligament stem cells (PDLSCs) react to mechanical force through proliferative, immunomodulatory, and regenerative actions that promote bone deposition. This study aimed to investigate how biomechanical compressive forces modulate PDLSCs' self-tolerance to proinflammatory responses.

METHODS

PDLSCs were cultured and characterized using flow cytometry. Intermittent compressive force (ICF) was applied to the cells using a computerized-controlled apparatus, with a force of 1.5 g/cm² at 0.23 Hz for 24 hours. TLR4 activation was induced using lipopolysaccharides (LPS) from P. gingivalis, in the presence or absence of ICF. Pathway inhibitors targeting TGF-β receptor type 1, Rho kinase, and NF-kB were applied to investigate the signaling pathways. Pro-inflammatory cytokine levels were measured using qPCR and ELISA. Western blotting was performed to assess the protein expression of TLR4 and TGF-β1. Immunofluorescence staining was used to localize TLR4. Osteogenic differentiation and IDO enzymatic activity were assessed.

RESULTS

Our results showed that PDLSCs primed with ICF developed tolerance to self-inflammatory responses when exposed to LPS, as indicated by reduced levels of inflammatory factors such as interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ. This tolerance, specific to ICF-primed PDLSCs, was partially mediated by the NF-kB p65 signaling pathway. Additionally, ICF enhanced PDLSC immunosuppressive properties and restored osteogenic differentiation, which had been delayed by LPS/TLR4 activation. Notably, TLR4 responded directly to ICF stimulation.

CONCLUSIONS

This study demonstrated that priming inflamed PDLSCs with biomechanical compressive force induces a tolerance effect against infection-induced inflammation, promoting bone regeneration.

CLINICAL SIGNIFICANCE

This study underscores the critical role of tolerance mechanisms in maintaining PDLSCs homeostasis, highlights the intricate interplay between biomechanical forces and immune modulation, and provides new insights into manipulating stem cells and developing therapeutic strategies to enhance bone and tissue regeneration in immune-related disorders, particularly periodontal disease.

Possible Association of Nrf2/ARE and NFκB Response to Osteoblast Function in Spheroid Culture Induced by Low-Intensity Pulsed Ultrasound (LIPUS)

OBJECTIVE

NFκB negatively affects bone metabolism through inflammatory pathways, whereas Nrf2 benefits it by regulating antioxidant/detoxifying enzymes through antioxidant response element (ARE) activity. We investigated whether low-intensity pulsed ultrasound (LIPUS) enhances osteogenic differentiation in 3D culture and whether it affects osteoblastic differentiation-associated markers such as calcium and alkaline phosphatase (ALP), and the regulation of NFκB and/or ARE.

METHODS

Murine MC3T3-E1 preosteoblasts were used to produce 3D-spheroids, which were treated with LIPUS. Time-dependent morphological change of spheroids was evaluated by microscopy, histology, and micro-CT. To analyze changes in ARE levels, a combination of LIPUS with an optimal concentration and timing of the Nrf2-inducer sulforaphane was applied. Osteoblast differentiation and mineralization were achieved through stimulation with differentiation medium for 21-28 days, during which LIPUS was used every day at 24-hour intervals. Differentiation was evaluated using calcium and ALP assay. Finally, cells were transduced with SIN-lenti-NFκB/SIN-lenti-ARE construct, and the effects of single-shot LIPUS on NFκB and ARE were evaluated using Nano-Glo® Luciferase Assay.

RESULTS

Morphologically, in LIPUS group, shrinkage behaviour, which may correlate with cell differentiation, was observed to be more pronounced. NFκB activity with LIPUS was significantly lower than without treatment, whereas ARE activity showed significant increase only immediately after LIPUS treatment. Conversely, LIPUS enhanced ARE activity in combination with sulforaphane administration. After 28 days, the calcium content and ALP activity of LIPUS-treated spheroids increased significantly.

CONCLUSION

This study suggests that LIPUS may have NFκB-downregulating, limited ARE-raising effects in combination with sulforaphane, and elevating osteoblast mineralization three-dimensionally. Thus, LIPUS could be useful for treating fractures in conditions of oxidative stress and hyper-inflammation.

Biomodulation effects induced by ultrasound stimulation in periodontal cells implicated in orthodontic tooth movement: A systematic review

Accelerating orthodontic tooth movement (OTM) is increasingly important for shorter treatment times, which reduces periodontal risks, root resorption and dental caries. Techniques to accelerate OTM focus on stimulating bone remodelling by enhancing osteoclast and osteoblast activity and include both surgical and non-surgical methods. The therapeutic potential of ultrasounds is highly recognized among many medical areas and has shown promising results in modulating bone remodelling and inflammation phenomena. This systematic review aims to collect and analyse the current scientific in vitro and ex vivo evidence on ultrasound stimulation (US) bioeffects in cells implicated in tooth movement. This review was conducted according to PRISMA 2020 guidelines. A bibliographic search was carried out in the PubMed, Scopus and Web of Science databases. Sixteen articles were selected and included in this review. The revised studies suggest that US of 1.0 and 1.5 MHz, delivered at 30 mW/cm2, 10 to 30 min daily over three to 14 days seems to be effective in promoting osteoclastogenic activity, while US of 1.5 MHz, 30 to 90 mW/cm2, in 5- to 20-min sessions delivered daily for 5 to 14 days exhibits the potential to stimulate osteogenic activity and differentiation. Previous research yielded varied evidence of the effectiveness of US in orthodontics. Future animal studies should employ the recommended US parameters and investigate how distinct protocols can differentially impact tissue remodelling pathways. The knowledge arising from this review will ultimately potentiate the application of US to accelerate OTM in the clinical setting.

Recent Advances in Basic Studies of Low-Intensity Pulsed Ultrasound in Periodontal Tissue Regeneration: A Systematic Review

Approximately half of the adult population is suffering from periodontal disease, and conventional periodontal treatment strategies can only slow the progression of the disease. As a kind of tissue engineering, periodontal regeneration brings hope for the treatment of periodontal disease. Low-intensity pulsed ultrasound (LIPUS) is a form of ultrasound with a frequency of 1-3 MHz and a much lower intensity (< 1W/cm2) than traditional ultrasound energy and output. LIPUS has been adopted for a variety of therapeutic purposes due to its bioeffects such as thermal, mechanical, and cavitation effects, which induce intracellular biochemical effects and lead to tissue repair and regeneration ultimately. In this systematic review, we summarize the basic research of LIPUS in the treatment of periodontal disease in periodontal disease animal models and the influence of LIPUS on the biological behavior (including promoting osteogenic differentiation of stem cells and inhibiting inflammatory response) and potential mechanism of periodontal ligament stem cells (PDLSCs), hoping to provide new ideas for the treatment of periodontal disease. We believe that LIPUS can be used as an auxiliary strategy in the treatment of periodontal disease and play an exciting and positive role in periodontal regeneration.

Plasticity Comparison of Two Stem Cell Sources with Different Hox Gene Expression Profiles in Response to Cobalt Chloride Treatment during Chondrogenic Differentiation

The limited self-repair capacity of articular cartilage is a challenge for healing injuries. While mesenchymal stem/stromal cells (MSCs) are a promising approach for tissue regeneration, the criteria for selecting a suitable cell source remain undefined. To propose a molecular criterion, dental pulp stem cells (DPSCs) with a Hox-negative expression pattern and bone marrow mesenchymal stromal cells (BMSCs), which actively express Hox genes, were differentiated towards chondrocytes in 3D pellets, employing a two-step protocol. The MSCs' response to preconditioning by cobalt chloride (CoCl2), a hypoxia-mimicking agent, was explored in an assessment of the chondrogenic differentiation's efficiency using morphological, histochemical, immunohistochemical, and biochemical experiments. The preconditioned DPSC pellets exhibited significantly elevated levels of collagen II and glycosaminoglycans (GAGs) and reduced levels of the hypertrophic marker collagen X. No significant effect on GAGs production was observed in the preconditioned BMSC pellets, but collagen II and collagen X levels were elevated. While preconditioning did not modify the ALP specific activity in either cell type, it was notably lower in the DPSCs differentiated pellets compared to their BMSCs counterparts. These results could be interpreted as demonstrating the higher plasticity of DPSCs compared to BMSCs, suggesting the contribution of their unique molecular characteristics, including their negative Hox expression pattern, to promote a chondrogenic differentiation potential. Consequently, DPSCs could be considered compelling candidates for future cartilage cell therapy.

Effect of autophagy on aging-related changes in orthodontic tooth movement in rats

BACKGROUND

The number of adult orthodontic patients is increasing, and studies have shown that autophagy is involved in regulating orthodontic tooth movement and plays an important role in aging-related changes. Therefore, we aimed to explore the role of autophagy in aging-related changes during orthodontic tooth movement by establishing a rat orthodontic tooth movement model.

METHODS

Forty-five 6-week-old and sixty-five 8-month-old male Sprague-Dawley rats were selected to represent adolescents and adults and establish orthodontic tooth movement model. They were sacrificed on days 0,1,3,7 and 14. Immunohistochemistry, immunofluorescence and tartrate resistant acid phosphatase (TRAP) staining were applied to measure the expression level of osteogenesis, autophagy, aging factors and osteoclast number in periodontal membrane of left upper first molar during orthodontic tooth movement. Then, we regulated the autophagy level by injecting autophagy activator rapamycin during orthodontic tooth movement and measured these factors and tooth movement distance by micro-computed tomography.

RESULTS

Aging factor levels in the periodontal membrane were higher in adult rats than in adolescent rats and the autophagy factor levels were lower. The levels of osteogenic factors were lower on the tension side in adult rats than in adolescent rats. The peak osteoclast number on the pressure side occurred later in adult rats than in adolescent rats. The injection of rapamycin increased autophagy, accelerated orthodontic tooth movement in adult rats, and reduced the levels of aging factors. The levels of osteogenic factors were higher and reached those in adolescent rats at some time points. The number of osteoclasts increased significantly in the early stage.

CONCLUSIONS

Autophagy may play a substantial role in regulating aging-related changes in orthodontic tooth movement.

Influence of Ultrasound Stimulation on the Viability, Proliferation and Protein Expression of Osteoblasts and Periodontal Ligament Fibroblasts

Among the adjunctive procedures to accelerate orthodontic tooth movement (OTM), ultrasound (US) is a nonsurgical form of mechanical stimulus that has been explored as an alternative to the currently available treatments. This study aimed to clarify the role of US in OTM by exploring different stimulation parameters and their effects on the biological responses of cells involved in OTM. Human fetal osteoblasts and periodontal ligament fibroblasts cell lines were stimulated with US at 1.0 and 1.5 MHz central frequencies and power densities of 30 and 60 mW/cm2 in continuous mode for 5 and 10 min. Cellular proliferation, metabolic activity and protein expression were analyzed. The US parameters that significantly improved the metabolic activity were 1.0 MHz at 30 mW/cm2 for 5 min and 1.0 MHz at 60 mW/cm2 for 5 and 10 min for osteoblasts; and 1.0 MHz at 30 mW/cm2 for 5 min and 1.5 MHz at 60 mW/cm2 for 5 and 10 min for fibroblasts. By stimulating with these parameters, the expression of alkaline phosphatase was maintained, while osteoprotegerin synthesis was induced after three days of US stimulation. The US stimulation improved the biological activity of both osteoblasts and periodontal ligament fibroblasts, inducing their osteogenic differentiation.

Latest progress in low-intensity pulsed ultrasound for studying exosomes derived from stem/progenitor cells

Stem cells have self-renewal, replication, and multidirectional differentiation potential, while progenitor cells are undifferentiated, pluripotent or specialized stem cells. Stem/progenitor cells secrete various factors, such as cytokines, exosomes, non-coding RNAs, and proteins, and have a wide range of applications in regenerative medicine. However, therapies based on stem cells and their secreted exosomes present limitations, such as insufficient source materials, mature differentiation, and low transplantation success rates, and methods addressing these problems are urgently required. Ultrasound is gaining increasing attention as an emerging technology. Low-intensity pulsed ultrasound (LIPUS) has mechanical, thermal, and cavitation effects and produces vibrational stimuli that can lead to a series of biochemical changes in organs, tissues, and cells, such as the release of extracellular bodies, cytokines, and other signals. These changes can alter the cellular microenvironment and affect biological behaviors, such as cell differentiation and proliferation. Here, we discuss the effects of LIPUS on the biological functions of stem/progenitor cells, exosomes, and non-coding RNAs, alterations involved in related pathways, various emerging applications, and future perspectives. We review the roles and mechanisms of LIPUS in stem/progenitor cells and exosomes with the aim of providing a deeper understanding of LIPUS and promoting research and development in this field.

Musculoskeletal Biomaterials: Stimulated and Synergized with Low Intensity Pulsed Ultrasound

Clinical biophysical stimulating strategies, which have significant effects on improving the function of organs or treating diseases by causing the salutary response of body, have shown many advantages, such as non-invasiveness, few side effects, and controllable treatment process. As a critical technique for stimulation, the low intensity pulsed ultrasound (LIPUS) has been explored in regulating osteogenesis, which has presented great promise in bone repair by delivering a combined effect with biomaterials. This review summarizes the musculoskeletal biomaterials that can be synergized with LIPUS for enhanced biomedical application, including bone regeneration, spinal fusion, osteonecrosis/osteolysis, cartilage repair, and nerve regeneration. Different types of biomaterials are categorized for summary and evaluation. In each subtype, the verified biological mechanisms are listed in a table or graphs to prove how LIPUS was effective in improving musculoskeletal tissue regeneration. Meanwhile, the acoustic excitation parameters of LIPUS that were promising to be effective for further musculoskeletal tissue engineering are discussed, as well as their limitations and some perspectives for future research. Overall, coupled with biomimetic scaffolds and platforms, LIPUS may be a powerful therapeutic approach to accelerate musculoskeletal tissue repair and even in other regenerative medicine applications.

Low intensity pulsed ultrasound reduces liver inflammation caused by fatigue exercise

Low-intensity pulsed ultrasound (LIPUS) has been shown to have many benefits, such as inhibiting inflammation, stimulating cell proliferation and differentiation, promoting angiogenesis, and so on. So, can exercise fatigue induced liver inflammation be effectively relieved by LIPUS? If possible, what is the possible mechanism? This study first investigated the effect of different intensity exercise on liver inflammation. Rats were divided into three groups: normal control group, exercise fatigue group, and aerobic exercise group. The results showed that aerobic exercise increases both anti-inflammatory factors and pro-inflammatory factors, while fatigue exercise decreases anti-inflammatory factors and increases pro-inflammatory factors, leading to severe liver injury and fibrosis. Then, we investigated the therapeutic effect of LIPUS on liver inflammation caused by exercise fatigue. Starting from the 6th week, the liver was irradiated with LIPUS of 80 mW/cm² for 20 min/d after daily exercise for 7 weeks. The results showed that LIPUS significantly decreased liver injury and fibrosis, significantly up-regulated the expression of STAT6, IL-13, and its receptors IL-13Rα1, and down regulated the expression of NF-κBp65 in exercise fatigue rats. These results indicate that LIPUS can reduce fatigue-induced liver inflammation, and the mechanism is related to the regulation of the IL-13/STAT6/NF-κBp65 pathway.