Effect of Low-Intensity Pulsed Ultrasound after Mesenchymal Stromal Cell Injection to Treat Osteochondral Defects: An In Vivo Study

Effectiveness of low-intensity pulsed ultrasound on osteoarthritis: molecular mechanism and tissue engineering

Osteoarthritis (OA) is distinguished by pathological alterations in the synovial membrane, articular cartilage, and subchondral bone, resulting in physical symptoms such as pain, deformity, and impaired mobility. Numerous research studies have validated the effectiveness of low-intensity pulsed ultrasound (LIPUS) in OA treatment. The periodic mechanical waves generated by LIPUS can mitigate cellular ischemia and hypoxia, induce vibration and collision, produce notable thermal and non-thermal effects, alter cellular metabolism, expedite tissue repair, improve nutrient delivery, and accelerate the healing process of damaged tissues. The efficacy and specific mechanism of LIPUS is currently under investigation. This review provides an overview of LIPUS's potential role in the treatment of OA, considering various perspectives such as the synovial membrane, cartilage, subchondral bone, and tissue engineering. It aims to facilitate interdisciplinary scientific research and further exploration of LIPUS as a complementary technique to existing methods or surgery. Ongoing research is focused on determining the optimal dosage, frequency, timing, and treatment strategy of LIPUS for OA. Additional research is required to clarify the precise mechanism of action and potential impacts on cellular, animal, and human systems prior to its integration into therapeutic applications.

The therapeutic effects of low-intensity pulsed ultrasound in musculoskeletal soft tissue injuries: Focusing on the molecular mechanism

Musculoskeletal soft tissue injuries are very common and usually occur during both sporting and everyday activities. The intervention of adjuvant therapies to promote tissue regeneration is of great importance to improving people's quality of life and extending their productive lives. Though many studies have focused on the positive results and effectiveness of the LIPUS on soft tissue, the molecular mechanisms standing behind LIPUS effects are much less explored and reported, especially the intracellular signaling pathways. We incorporated all research on LIPUS in soft tissue diseases since 2005 and summarized studies that uncovered the intracellular molecular mechanism. This review will also provide the latest evidence-based research progress in this field and suggest research directions for future experiments.

Low-Intensity Pulsed Ultrasound Promotes Osteogenic Potential of iPSC-Derived MSCs but Fails to Simplify the iPSC-EB-MSC Differentiation Process

Induced pluripotent stem cell (iPSC)-derived mesenchymal stem cells (iMSCs) are a promising cell source for bone tissue engineering. However, iMSCs have less osteogenic potential than BMSCs, and the classical iPSC-EB-iMSC process to derive iMSCs from iPSCs is too laborious as it involves multiple in vitro steps. Low-intensity pulsed ultrasound (LIPUS) is a safe therapeutic modality used to promote osteogenic differentiation of stem cells. Whether LIPUS can facilitate osteogenic differentiation of iMSCs and simplify the iPSC-EB-iMSC process is unknown. We stimulated iMSCs with LIPUS at different output intensities (20, 40, and 60 mW/cm²) and duty cycles (20, 50, and 80%). Results of ALP activity assay, osteogenic gene expression, and mineralization quantification demonstrated that LIPUS was able to promote osteogenic differentiation of iMSCs, and it worked best at the intensity of 40 mW/cm² and the duty cycle of 50% (LIPUS40/50). The Wnt/β-catenin signaling pathway was involved in LIPUS40/50-mediated osteogenesis. When cranial bone defects were implanted with iMSCs, LIPUS40/50 stimulation resulted in a significant higher new bone filling rate (72.63 ± 17.04)% than the non-stimulated ones (34.85 ± 4.53)%. Daily exposure to LIPUS40/50 may accelerate embryoid body (EB)-MSC transition, but it failed to drive iPSCs or EB cells to an osteogenic lineage directly. This study is the first to demonstrate the pro-osteogenic effect of LIPUS on iMSCs. Although LIPUS40/50 failed to simplify the classical iPSC-EB-MSC differentiation process, our preliminary results suggest that LIPUS with a more suitable parameter set may achieve the goal. LIPUS is a promising method to establish an efficient model for iPSC application.

The Paracrine Function of Mesenchymal Stem Cells in Response to Pulsed Focused Ultrasound

We studied the paracrine function of mesenchymal stem cells (MSCs) derived from various sources in response to pulsed focused ultrasound (pFUS). Human adipose tissue (AD), bone marrow (BM), and umbilical cord (UC) derived MSCs were exposed to pFUS at two intensities: 0.45 W/cm² I_SATA (310 kPa PNP) and 1.3 W/cm² I_SATA (540 kPa PNP). Following pFUS, the viability and proliferation of MSCs were assessed using a hemocytometer and confocal microscopy, and their secreted cytokine profile determined using a multiplex ELISA. Our findings showed that pFUS can stimulate the production of immunomodulatory, anti-inflammatory, and angiogenic cytokines from MSCs which was dependent on both the source of MSC being studied and the acoustic intensity employed. These important findings set the foundation for additional mechanistic and validation studies using this novel noninvasive and clinically translatable technology for modulating MSC biology.

Low-intensity pulsed ultrasound protects subchondral bone in rabbit temporomandibular joint osteoarthritis by suppressing TGF-β1/Smad3 pathway

Transforming growth factor β1(TGF-β1)/Smad3 pathway promotes the pathological progression of subchondral bone in osteoarthritis. The aim of this study is to determine the effect of low-intensity pulsed ultrasound (LIPUS) on the pathological progression and TGF-β1/Smad3 pathway of subchondral bone in temporomandibular joint osteoarthritis (TMJOA). Rabbit TMJOA model was established by type II collagenase induction. The left joint in this model was continuously stimulated with LIPUS for 3 and 6 weeks (1 MHz; 30 mW/cm² ) for 20 min/day. The morphological and histological features of subchondral bone were respectively examined by microcomputed tomography and Safranin-O staining. The number of osteoclasts was quantitatively assessed by tartrate-resistant acid phosphatase staining. Immunohistochemistry and Western blot analysis were conducted to evaluate the protein expression of Cathepsin K and TGF-β1/Smad3 pathway. The results indicated that LIPUS could improve the trabecular microstructure and histological characteristics of subchondral bone in rabbit TMJOA. It also suppressed abnormal subchondral bone resorption and activation of TGF-β1/Smad3 pathway, characterized by the number of osteoclasts, protein expression levels of Cathepsin K, TGF-β1, type II TGFβ receptor, and phosphorylated Smad3 (pSmad3) were decreased. In conclusion, LIPUS promoted the quality of subchondral bone by suppressing osteoclast activity and TGF-β1/Smad3 pathway in rabbit TMJOA.

Ultrasound Therapy: Experiences and Perspectives for Regenerative Medicine

Ultrasound has emerged as a novel tool for clinical applications, particularly in the context of regenerative medicine. Due to its unique physico-mechanical properties, low-intensity ultrasound (LIUS) has been approved for accelerated fracture healing and for the treatment of established non-union, but its utility has extended beyond tissue engineering to other fields, including cell regeneration. Cells and tissues respond to acoustic ultrasound by switching on genetic repair circuits, triggering a cascade of molecular signals that promote cell proliferation, adhesion, migration, differentiation, and extracellular matrix production. LIUS also induces angiogenesis and tissue regeneration and has anti-inflammatory and anti-degenerative effects. Accordingly, the potential application of ultrasound for tissue repair/regeneration has been tested in several studies as a stand-alone treatment and, more recently, as an adjunct to cell-based therapies. For example, ultrasound has been proposed to improve stem cell homing to target tissues due to its ability to create a transitional and local gradient of cytokines and chemokines. In this review, we provide an overview of the many applications of ultrasound in clinical medicine, with a focus on its value as an adjunct to cell-based interventions. Finally, we discuss the various preclinical and clinical studies that have investigated the potential of ultrasound for regenerative medicine.

The role of ultrasound in enhancing mesenchymal stromal cell-based therapies

Mesenchymal stromal cells (MSCs) have been a popular platform for cell‐based therapy in regenerative medicine due to their propensity to home to damaged tissue and act as a repository of regenerative molecules that can promote tissue repair and exert immunomodulatory effects. Accordingly, a great deal of research has gone into optimizing MSC homing and increasing their secretion of therapeutic molecules. A variety of methods have been used to these ends, but one emerging technique gaining significant interest is the use of ultrasound. Sound waves exert mechanical pressure on cells, activating mechano‐transduction pathways and altering gene expression. Ultrasound has been applied both to cultured MSCs to modulate self‐renewal and differentiation, and to tissues‐of‐interest to make them a more attractive target for MSC homing. Here, we review the various applications of ultrasound to MSC‐based therapies, including low‐intensity pulsed ultrasound, pulsed focused ultrasound, and extracorporeal shockwave therapy, as well as the use of adjunctive therapies such as microbubbles. At a molecular level, it seems that ultrasound transiently generates a local gradient of cytokines, growth factors, and adhesion molecules that facilitate MSC homing. However, the molecular mechanisms underlying these methods are far from fully elucidated and may differ depending on the ultrasound parameters. We thus put forth minimal criteria for ultrasound parameter reporting, in order to ensure reproducibility of studies in the field. A deeper understanding of these mechanisms will enhance our ability to optimize this promising therapy to assist MSC‐based approaches in regenerative medicine.

Human adipose-derived Mesenchymal stem cells, low-intensity pulsed ultrasound, or their combination for the treatment of knee osteoarthritis: study protocol for a first-in-man randomized controlled trial

Background

Human adipose-derived Mesenchymal stem cells (HADMSCs) have proven their efficacy in treating osteoarthritis (OA), in earlier preclinical and clinical studies. As the tissue repairers are under the control of mechanical and biochemical signals, improving regeneration outcomes using such signals has of late been the focus of attention. Among mechanical stimuli, low-intensity pulsed ultrasound (LIPUS) has recently shown promise both in vitro and in vivo. This study will investigate the potential of LIPUS in enhancing the regeneration process of an osteoarthritic knee joint.

Methods

This study involves a prospective, randomized, placebo-controlled, and single-blind trial based on the SPIRIT guidelines, and aims to recruit 96 patients initially diagnosed with knee osteoarthritis, following American College of Rheumatology criteria. Patients will be randomized in a 1:1:1 ratio to receive Intraarticular HADMSCs injection with LIPUS, Intraarticular HADMSCs injection with shame LIPUS, or Normal saline with LIPUS. The primary outcome is Western Ontario and McMaster Universities Index of OA (WOMAC) score, while the secondary outcomes will be other knee structural changes, and lower limb muscle strength such as the knee cartilage thickness measured by MRI. Blinded assessments will be performed at baseline (1 month prior to treatment), 1 month, 3 months, and 6 months following the interventions.

Discussion

This trial will be the first clinical study to comprehensively investigate the safety and efficacy of LIPUS on stem cell therapy in OA patients. The results may provide evidence of the effectiveness of LIPUS in improving stem cell therapy and deliver valuable information for the design of subsequent trials.

Trial registration

This study had been prospectively registered with the Chinese Clinical Trials Registry. registration number: ChiCTR1900025907 at September 14, 2019.

Preconditioning of mesenchymal stromal cells with low-intensity ultrasound: influence on chondrogenesis and directed SOX9 signaling pathways

Background

Continuous low-intensity ultrasound (cLIUS) facilitates the chondrogenic differentiation of human mesenchymal stromal cells (MSCs) in the absence of exogenously added transforming growth factor-beta (TGFβ) by upregulating the expression of transcription factor SOX9, a master regulator of chondrogenesis. The present study evaluated the molecular events associated with the signaling pathways impacting SOX9 gene and protein expression under cLIUS.

Methods

Human bone marrow-derived MSCs were exposed to cLIUS stimulation at 14 kPa (5 MHz, 2.5 Vpp) for 5 min. The gene and protein expression of SOX9 was evaluated. The specificity of SOX9 upregulation under cLIUS was determined by treating the MSCs with small molecule inhibitors of select signaling molecules, followed by cLIUS treatment. Signaling events regulating SOX9 expression under cLIUS were analyzed by gene expression, immunofluorescence staining, and western blotting.

Results

cLIUS upregulated the gene expression of SOX9 and enhanced the nuclear localization of SOX9 protein when compared to non-cLIUS-stimulated control. cLIUS was noted to enhance the phosphorylation of the signaling molecule ERK1/2. Inhibition of MEK/ERK1/2 by PD98059 resulted in the effective abrogation of cLIUS-induced SOX9 expression, indicating that cLIUS-induced SOX9 upregulation was dependent on the phosphorylation of ERK1/2. Inhibition of integrin and TRPV4, the upstream cell-surface effectors of ERK1/2, did not inhibit the phosphorylation of ERK1/2 and therefore did not abrogate cLIUS-induced SOX9 expression, thereby suggesting the involvement of other mechanoreceptors. Consequently, the effect of cLIUS on the actin cytoskeleton, a mechanosensitive receptor regulating SOX9, was evaluated. Diffused and disrupted actin fibers observed in MSCs under cLIUS closely resembled actin disruption by treatment with cytoskeletal drug Y27632, which is known to increase the gene expression of SOX9. The upregulation of SOX9 under cLIUS was, therefore, related to cLIUS-induced actin reorganization. SOX9 upregulation induced by actin reorganization was also found to be dependent on the phosphorylation of ERK1/2.

Conclusions

Collectively, preconditioning of MSCs by cLIUS resulted in the nuclear localization of SOX9, phosphorylation of ERK1/2 and disruption of actin filaments, and the expression of SOX9 was dependent on the phosphorylation of ERK1/2 under cLIUS.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1532-2) contains supplementary material, which is available to authorized users.

Continuous Low-Intensity Ultrasound Promotes Native-to-Native Cartilage Integration

Failure of the host/graft interface to integrate impedes the success of cartilage repair protocols. Continuous low-intensity ultrasound (cLIUS) at the resonant frequency of 5 MHz is proposed as a treatment modality for promoting native-to-native cartilage integration in vitro. Cylindrical incisions (4 mm) simulating chondral discontinuity were made in bovine cartilage and osteochondral explants, and maintained under cLIUS stimulation (14 kPa [5 MHz, 2.5 Vpp], 20 min, four times/day) for 28 days. Incised cartilage and osteochondral explants were categorized into three study groups; Group I: cLIUS was applied immediately upon incision; Group II: cLIUS was applied after 14 days following incision; Group-III: after 14 days following incision, explants were treated with 0.1% hyaluronidase and 30 U/mL collagenase VII. As a separate study group, incised osteochondral explants were treated immediately with cLIUS at a nonresonant frequency of 2 MHz (14 kPa [2 MHz, 6 Vpp], 20 min, four times/day). Cellular migration was analyzed by scratch assays, and by visualizing migrating cells into the hydrogel core of cartilage/hydrogel constructs. Explants under cLIUS (5 MHz) displayed higher percent apposition along with gap closures when compared with untreated controls and explants treated with cLIUS at 2 MHz. cLIUS (5 MHz)-treated explants were immunopositive for type II collagen. The strength of native-to-native cartilage integration was higher (p = 0.005) in cLIUS-treated cartilage explants at 0.19 ± 0.08 MPa as compared with 0.05 ± 0.03 MPa in untreated controls. Enhanced cartilage phenotype coupled with increased cellular migration were noted under cLIUS (5 MHz), alluding to the observed integration between cartilage interfaces. Collectively, cLIUS at cell resonant frequency promoted integrative cartilage repair, therefore, has the potential to improve cartilage repair outcomes. Impact Statement Lack of integration between the host and graft cartilage interfaces impedes the success of cartilage repair techniques. Continuous low-intensity ultrasound (cLIUS) is documented to induce chondrogenesis and chondrocyte phenotype. However, integrative cartilage repair under cLIUS has not been evaluated. Our results demonstrated integration between cartilage interfaces, increased percent apposition, increased strength of integration, and maintenance of cartilage phenotype under cLIUS (5 MHz). Integrative repair under cLIUS (5 MHz) stemmed from enhanced migration of cells and increased expression of cartilage-specific genes, namely SOX9 and COL2A1. Thus, cLIUS has the potential to improve the outcomes of grafting protocols for cartilage repair.

Low-Intensity Pulsed Ultrasound Relieves Mild and Severe Myelosuppression Induced by Cyclophosphamide in Rabbits

OBJECTIVE

This study aimed to investigate the effect of low-intensity pulsed ultrasound (LIPUS) on cyclophosphamide (CTX)-induced rabbit myelosuppression.

METHODS

Rabbits (n = 90) were randomly divided into a mild myelosuppression group (n = 40), a severe myelosuppression group (n = 40), and a normal control group (group Cu₂₈ ; n = 10). The mild and severe myelosuppression models were established by daily ear vein injection of 15- and 40-mg/kg CTX for 4 continuous days, respectively. Then they were randomly divided into LIPUS groups (A_u and B_u ) and control groups (A_c and B_c ). LIPUS was applied once per day for 20 minutes for 7 (A_u7 and B_u7 ) and 28 (A_u28 and B_u28 ) days. Physical conditions, mortality, blood cell counts, and bone marrow proliferation were calculated. Erythropoietin interleukin 3, and granulocyte-macrophage colony-stimulating factor levels were measured by an enzyme-linked immunosorbent assay. Flow cytometry was used to detect the granulocyte phagocytosis rate. Hematoxylin-eosin staining was performed to analyze changes of skin and muscle.

RESULTS

Compared with the control group, LIPUS improved the number of peripheral blood cells (P < .05) and bone marrow nucleated cells and reduced the mortality of rabbits with myelosuppression of different degrees. Long-term treatment for 28 days had no effect on the levels of erythropoietin, interleukin 3, and granulocyte-macrophage colony-stimulating factor and granulocyte phagocytosis (P > .05). The parts of the skin where LIPUS was applied did not show any burning marks, and the muscle tissue in the path of LIPUS acoustic channels showed no obvious pathologic changes.

CONCLUSIONS

Low-intensity pulsed ultrasound is a safe and effective method to relieve CTX-induced myelosuppression.

Effect of Low-Intensity Pulsed Ultrasound After Autologous Adipose-Derived Stromal Cell Transplantation for Bone-Tendon Healing in a Rabbit Model

BACKGROUND

Low-intensity pulsed ultrasound (LIPUS), as a safe biophysiotherapy, can enhance bone-tendon (B-T) healing in vivo and induce osteogenic or chondrogenic differentiation of mesenchymal stromal cells in vitro. This study aimed to determine whether LIPUS can improve the efficacy of transplanted mesenchymal stromal cells on B-T healing.

HYPOTHESIS

LIPUS can induce lineage-specific differentiation of transplanted adipose-derived stromal cells (ASCs) at the B-T healing site, thus resulting in superior healing quality when compared with LIPUS or ASCs alone.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 112 mature rabbits with partial patellectomy in the hindlimb were randomly assigned into mock sonication without ASCs (control), ultrasonication without ASCs (LIPUS), mock sonication with ASCs (ASCs), and ultrasonication with ASCs (LIPUS + ASCs). The treatment time of the mock sonication or ultrasonication was 20 minutes per day. Autologous ASCs were transplanted to the healing site by fibrin glue during the operation, and LIPUS was delivered daily starting at postoperative day 3 until euthanasia. The patella-patellar tendon junctions were postoperatively harvested at 8 and 16 weeks for radiological, histological, and mechanical evaluations. Additionally, 9 animals were used for ASC tracking with mCherry protein.

RESULTS

Radiologically, there was more new bone formation and remodeling in the LIPUS + ASCs group as compared with the other groups. Synchrotron radiation micro-computed tomography showed that the LIPUS + ASCs group significantly increased bone volume fraction, trabecular thickness, and trabecular number at the healing site as compared with the other groups at postoperative 8 weeks ( P < .05 for all). Histologically, immunohistochemical staining confirmed that the transplanted mCherry-ASCs can differentiate into osteoblasts and fibrochondrocytic-like cells. Meanwhile, as compared with the other groups, the LIPUS + ASCs group showed more formation and maturity of the fibrocartilage layer and new bone at postoperative weeks 8 and 16 ( P < .05 for all). Biomechanically, the LIPUS + ASCs group showed significantly higher failure load and stiffness versus the other groups at postoperative weeks 8 and 16 ( P < .05 for all).

CONCLUSION

Autologous ASC transplantation stimulated with LIPUS can result in superior B-T healing quality when compared with LIPUS or ASCs alone.

CLINICAL RELEVANCE

This study demonstrates the effectiveness of using ASC transplantation stimulated with LIPUS for B-T healing and provides a foundation for future clinical studies.

Effectiveness of mesenchymal stem cells for treating patients with knee osteoarthritis: a meta-analysis toward the establishment of effective regenerative rehabilitation

This systematic review with a meta-analysis aimed to summarize the current evidence of the effectiveness of mesenchymal stem cell (MSC) treatment for knee osteoarthritis (OA) and to examine whether rehabilitation is an effect modifier of the effect estimate of MSC treatment. A literature search yielded 659 studies, of which 35 studies met the inclusion criteria (n = 2385 patients; mean age: 36.0-74.5 years). The meta-analysis results suggested that MSC treatment through intra-articular injection or arthroscopic implantation significantly improved knee pain (standardized mean difference [SMD]: -1.45, 95% confidence interval [CI]: -1.94, -0.96), self-reported physical function (SMD: 1.50, 95% CI: 1.09, 1.92), and cartilage quality (SMD: -1.99; 95% CI: -3.51, -0.47). However, the MSC treatment efficacy on cartilage volume was limited (SMD: 0.49; 95% CI: -0.19, 1.16). Minor adverse events (knee pain or swelling) were reported with a wide-ranging prevalence of 2-60%; however, no severe adverse events occurred. The evidence for these outcomes was "very low" to "low" according to the Grades of Recommendation, Assessment, Development and Evaluation system because of the poor study design, high risk of bias, large heterogeneity, and wide 95% CI of the effects estimate. Performing rehabilitation was significantly associated with better SMD for self-reported physical function (regression coefficient: 0.881, 95% CI: 0.049, 1.712; P = 0.039). We suggest that more high quality randomized controlled trials with consideration of the potential rehabilitation-driven clinical benefit would be needed to facilitate the foundation of effective MSC treatment and regenerative rehabilitation for patients with knee OA.