Low-intensity pulsed ultrasound enhances BMP-7-induced osteogenic differentiation of human fracture hematoma-derived progenitor cells in vitro

Management of non-unions of the malleolar fractures- Current Evidence

Although malleolar non-union is uncommon, it is associated with significant morbidity. Managing this problem requires understanding ankle fracture biomechanics and bone healing. We present in this article the pertinent points to be considered in evaluating and managing patients with malleolar non-union. Our discussion will focus on the important risk factors contributing to this problem, and the need to carefully consider the biomechanical stability and the biological environment to ensure successful bony unions.

Effect of low-intensity pulsed ultrasound on osteogenic differentiation of human induced membrane-derived cells in Masquelet technique

INTRODUCTION

The Masquelet technique is a relatively new method for large bone defect treatment. In this technique, grafted bone tissue is used, and after the cement is removed, the induced membrane (IM; that form around the cement spacers placed in the bone defect region) is thought to play an important role in promoting bone formation. On the other hand, low-intensity pulsed ultrasound (LIPUS) is known to promote fracture healing and angiogenesis through mechanical stimulation. This study aimed to investigate the in vitro effects of LIPUS on the osteogenic differentiation of human induced membrane-derived cells (IMCs).

METHODS

Seven patients who had been treated using the Masquelet technique were enrolled. The IM was harvested during the second stage of the technique. IMCs were isolated, cultured in growth medium, and then divided into two groups: (1) control group, IMCs cultured in osteogenic medium without LIPUS, and (2) LIPUS group, IMCs cultured in osteogenic medium with LIPUS treatment. Adherent cells from the IM samples were harvested after the first passage and evaluated for cell surface protein expression using immunostaining. A cell proliferation assay was used to count the number of IMCs using a hemocytometer. Osteogenic differentiation capability was assessed using an alkaline phosphatase (ALP) activity assay, Alizarin Red S staining, and real-time reverse transcription-polymerase chain reaction.

RESULTS

Cell surface antigen profiling revealed that the IMCs contained cells positive for the mesenchymal stem cell-related markers CD73, CD90, and CD105. No significant difference in cell numbers was found between the control and LIPUS groups. The ALP activity of IMCs in the LIPUS group was significantly higher than that in the control group on days 7 and 14. Alizarin red S staining intensity was significantly higher in the LIPUS group than in the control group on day 21. Runx2 and VEGF expression was significantly upregulated on days 7 and 14, respectively, compared with levels in the control group.

CONCLUSION

We demonstrated the significant effect of LIPUS on the osteogenic differentiation of human IMCs. This study indicates that LIPUS can be used as an additional tool for the enhancement of the healing process of the Masquelet technique.

Low-Intensity Pulsed Ultrasound Promotes Osteogenic Differentiation of Reamer-Irrigator-Aspirator Graft-Derived Cells in Vitro

Recently, reamer-irrigator-aspirator (RIA) systems have been increasingly used to harvest autologous bone grafts. RIA graft materials contain bone marrow, which provides a viable source to derive large numbers of mesenchymal stem cells. Low-intensity pulsed ultrasound (LIPUS) significantly accelerates the differentiation of stem cells derived from bone marrow. This in vitro study investigated the effect of LIPUS on the osteogenic activity and differentiation of RIA graft-derived cells. A small amount of RIA graft was obtained from seven patients. After the cells derived from RIA grafts were cultured, they were divided into two groups: the LIPUS and control groups. LIPUS was applied once daily for 20 min (1.5 MHz, pulse duration: 200 µs, pulse repetition rate: 1 kHz, spatial average-temporal average intensity: 30 mW/cm²). Alkaline phosphatase activity (113.4% and 130.1% on days 7 and 14), expression of osteoblast-related genes (ALP, Runx2) and mineralization (135.2% on day 21) of the RIA graft-derived cells were significantly higher in the LIPUS group than in the control group. However, LIPUS did not affect the cell proliferation of RIA graft-derived cells. This study indicates that LIPUS may enhance the healing of non-union and critical bone defects treated by autologous bone grafting using the RIA system.

Effects of ultrasound, radial extracorporeal shock waves, and electrical stimulation on rat bone defect healing

Fractures associated with osteoporosis are a major public health concern. Current treatments for fractures are limited to surgery or fixation, leading to long-term bedrest, which is linked to increased mortality. Alternatively, utilization of physical agents has been suggested as a promising therapeutic approach for fractures. Here, we examined the effects of ultrasound, radial extracorporeal shock waves, and electrical stimulation on normal or osteoporotic fracture healing. Femoral bone defects were created in normal or ovariectomized rats. Rats were divided into four groups: untreated, and treated with ultrasound, shock waves, or electrical stimulation after surgery. Samples were collected at 2 or 4 weeks after surgery, and the healing process was evaluated with micro-CT, histological, and immunohistochemical analyses. Ultrasound at intensities of 0.5 and 1.0 W/cm² , but not 0.05 W/cm² , accelerated new bone formation. Shock wave exposure also increased newly formed bone, but formed abnormal periosteal callus around the defect site. Conversely, electrical stimulation did not affect the healing process. Ultrasound exposure increased osteoblast activity and cell proliferation and decreased sclerostin-positive osteocytes. We demonstrated that higher-intensity ultrasound and radial extracorporeal shock waves accelerate fracture healing, but shock wave treatment may increase the risk of periosteal callus formation.

Impact of Ultrasound Therapy on Stem Cell Differentiation - A Systematic Review

OBJECTIVE

This is a systematic review of the effects of low-intensity pulsed ultrasound (LIPUS) on stem cell differentiation.

BACKGROUND DATA

Recent studies have investigated several types of stem cells from different sources in the body. These stem cells should strictly be certified and promoted for cell therapies before being used in medical applications. LIPUS has been used extensively in treatment centers and in research to promote stem cell differentiation, function, and proliferation.

MATERIALS AND METHODS

The databases of PubMed, Google Scholar, and Scopus were searched for abstracts and full-text scientific papers published from 1989-2019 that reported the application of LIPUS on stem cell differentiation. Related English language articles were found using the following defined keywords: low-intensity pulsed ultrasound, stem cell, differentiation. Criteria for inclusion in the review were: LIPUS with frequencies of 1-3 MHz and pulsed ultrasound intensity of <500 mW/cm2. Duration, exposure time, and cell sources were taken into consideration.

RESULTS

Fifty-two articles were selected based on the inclusion criteria. Most articles demonstrated that the application of LIPUS had positive effects on stem cell differentiation. However, some authors recommended that LIPUS combined with other physical therapy aides was more effective in stem cell differentiation.

CONCLUSION

LIPUS significantly increases the level of stem cell differentiation in cells derived mainly from bone marrow mesenchymal stem cells. There is a need for further studies to analyze the effect of LIPUS on cells derived from other sources, particularly adipose tissue-derived mesenchymal stem cells, for treating hard diseases, such as osteoporosis and diabetic foot ulcer. Due to a lack of reporting on standard LIPUS parameters in the field, more experiments comparing the protocols for standardization of LIPUS parameters are needed to establish the best protocol, which would allow for the best results.

Physical Stimulations for Bone and Cartilage Regeneration

A wide range of techniques and methods are actively invented by clinicians and scientists who are dedicated to the field of musculoskeletal tissue regeneration. Biological, chemical, and physiological factors, which play key roles in musculoskeletal tissue development, have been extensively explored. However, physical stimulation is increasingly showing extreme importance in the processes of osteogenic and chondrogenic differentiation, proliferation and maturation through defined dose parameters including mode, frequency, magnitude, and duration of stimuli. Studies have shown manipulation of physical microenvironment is an indispensable strategy for the repair and regeneration of bone and cartilage, and biophysical cues could profoundly promote their regeneration. In this article, we review recent literature on utilization of physical stimulation, such as mechanical forces (cyclic strain, fluid shear stress, etc.), electrical and magnetic fields, ultrasound, shock waves, substrate stimuli, etc., to promote the repair and regeneration of bone and cartilage tissue. Emphasis is placed on the mechanism of cellular response and the potential clinical usage of these stimulations for bone and cartilage regeneration.

Low-intensity pulsed ultrasound activates ERK1/2 and PI3K-Akt signalling pathways and promotes the proliferation of human amnion-derived mesenchymal stem cells

OBJECTIVES

This study was to investigate the effect and mechanism of low-intensity pulsed ultrasound (LIPUS) on the proliferation of human amnion-derived mesenchymal stem cells (hAD-MSCs).

METHODS

Human amnion-derived mesenchymal stem cells were isolated from the amnion of term placentas and identified by flow cytometry and differentiation culture. Proliferation of hAD-MSCs was investigated by Cell Counting Kit-8, cell cycle and EdU assays. Western blotting was used to determine the protein expression levels.

RESULTS

Human amnion-derived mesenchymal stem cells were successfully isolated from the amnion and identified as multipotent mesenchymal stem cells. Low-intensity pulsed ultrasound promoted the proliferation of hAD-MSCs. Cell cycle analysis showed that LIPUS promoted cells to enter S and G2/M phases from G0/G1 phase. Western blot results showed that LIPUS promoted the phosphorylation and activation of ERK1/2 and Akt and significantly upregulated expression of cyclin D1, cyclin E1, cyclin A2 and cyclin B1. ERK1/2 inhibitor (U0126) and PI3K inhibitor (LY294002) significantly reduced LIPUS-induced phosphorylation of ERK1/2 and Akt, respectively, which in turn reduced the LIPUS-induced proliferation of hAD-MSCs.

CONCLUSIONS

Low-intensity pulsed ultrasound can promote the proliferation of hAD-MSCs, and ERK1/2 and PI3K-Akt signalling pathways may play important roles in this process.

Treatment of Nonunions After Malleolar Fractures

Ankle fracture nonunion is a rare occurrence following closed or operative intervention. When it does occur, patients can experience debilitating symptoms that limit daily function. Malleolar nonunion can be caused by patient factors, such as smoking, malnutrition, or vascular insufficiency. Surgeon factors, such as insufficient or inappropriate operative fixation, also play a role. Several adjuncts, such as bone grafting, bone morphogenic protein, and bone stimulation, are useful in treating nonunions. Through a multimodal approach, malleolar nonunions are reliably treated with operative fixation leading to good patient outcomes with minimal complications.

Stimulation of Bone Repair with Ultrasound

This chapter reviews the different options available for the use of ultrasound in the enhancement of fracture healing or in the reactivation of a failed healing process: LIPUS, shock waves and ultrasound-mediated delivery of bioactive molecules, such as growth factors or plasmids. The main emphasis is on LIPUS, or Low Intensity Pulsed Ultrasound, the most widespread and studied technique. LIPUS has pronounced bioeffects on tissue regeneration, while employing intensities within a diagnostic range. The biological response to LIPUS is complex as the response of numerous cell types to this stimulus involves several pathways. Known to-date mechanotransduction pathways involved in cell responses include MAPK and other kinases signaling pathways, gap-junctional intercellular communication, up-regulation and clustering of integrins, involvement of the COX-2/PGE2 and iNOS/NO pathways, and activation of the ATI mechanoreceptor. Mechanisms at the origin of LIPUS biological effects remain intriguing, and analysis is hampered by the diversity of experimental systems used in-vitro. Data point to clear evidence that bioeffects can be modulated by direct and indirect mechanical effects, like acoustic radiation force, acoustic streaming, propagation of surface waves, heat, fluid-flow induced circulation and redistribution of nutrients, oxygen and signaling molecules. One of the future engineering challenge is therefore the design of dedicated experimental set-ups allowing control of these different mechanical phenomena, and to relate them to biological responses. Then, the derivation of an 'acoustic dose' and the cross-calibration of the different experimental systems will be possible. Despite this imperfect knowledge of LIPUS biophysics, the clinical evidence, although most often of low quality, speaks in favor of the clinical use of LIPUS, when the economics of nonunion and the absence of toxicity of this ultrasound technology are taken into account.

Stimulation of bone repair with ultrasound: a review of the possible mechanic effects

In vivo and in vitro studies have demonstrated the positive role that ultrasound can play in the enhancement of fracture healing or in the reactivation of a failed healing process. We review the several options available for the use of ultrasound in this context, either to induce a direct physical effect (LIPUS, shock waves), to deliver bioactive molecules such as growth factors, or to transfect cells with osteogenic plasmids; with a main focus on LIPUS (or Low Intensity Pulsed Ultrasound) as it is the most widespread and studied technique. The biological response to LIPUS is complex as numerous cell types respond to this stimulus involving several pathways. Known to-date mechanotransduction pathways involved in cell responses include MAPK and other kinases signaling pathways, gap-junctional intercellular communication, up-regulation and clustering of integrins, involvement of the COX-2/PGE2, iNOS/NO pathways and activation of ATI mechanoreceptor. The mechanisms by which ultrasound can trigger these effects remain intriguing. Possible mechanisms include direct and indirect mechanical effects like acoustic radiation force, acoustic streaming, and propagation of surface waves, fluid-flow induced circulation and redistribution of nutrients, oxygen and signaling molecules. Effects caused by the transformation of acoustic wave energy into heat can usually be neglected, but heating of the transducer may have a potential impact on the stimulation in some in-vitro systems, depending on the coupling conditions. Cavitation cannot occur at the pressure levels delivered by LIPUS. In-vitro studies, although not appropriate to identify the overall biological effects, are of great interest to study specific mechanisms of action. The diversity of current experimental set-ups however renders this analysis very complex, as phenomena such as transducer heating, inhomogeneities of the sound intensity in the near field, resonances in the transmission and reflection through the culture dish walls and the formation of standing waves will greatly affect the local type and amplitude of the stimulus exerted on the cells. A future engineering challenge is therefore the design of dedicated experimental set-ups, in which the different mechanical phenomena induced by ultrasound can be controlled. This is a prerequisite to evaluate the biological effects of the different phenomena with respect to particular parameters, like intensity, frequency, or duty cycle. By relating the variations of these parameters to the induced physical effects and to the biological responses, it will become possible to derive an 'acoustic dose' and propose a quantification and cross-calibration of the different experimental systems. Improvements in bone healing management will probably also come from a combination of ultrasound with a 'biologic' components, e.g. growth factors, scaffolds, gene therapies, or drug delivery vehicles, the effects of which being potentiated by the ultrasound.

BMP growth factor signaling in a biomechanical context

Bone Morphogenetic Proteins (BMPs) are members of the transforming growth factor-β superfamily of secreted polypeptide growth factors and are important regulators in a multitude of cellular processes. To ensure the precise and balanced propagation of their pleiotropic signaling responses, BMPs and their corresponding signaling pathways are subject to tight control. A large variety of regulatory mechanisms throughout different biological levels combines into a complex network and provides the basis for physiological BMP function. This regulatory network not only includes biochemical factors but also mechanical cues. Both BMP signaling and mechanotransduction pathways are tightly interconnected and represent an elaborate signaling network active during development but also during organ homeostasis. Moreover, its dysregulation is associated with a number of human pathologies. A more detailed understanding of this crosstalk in respect to molecular interactions will be indispensable in the future, in particular to understand BMP-related diseases as well as with regard to an efficient clinical application of BMP ligands.

Effects of parathyroid hormone 1-34 on osteogenic and chondrogenic differentiation of human fracture haematoma-derived cells in vitro

Parathyroid hormone (PTH) 1-34 has been shown to accelerate fracture healing. Previously, we reported that progenitor cells with osteogenic and chondrogenic potential exist in human fracture haematoma, suggesting that the fracture haematoma-derived progenitor cells (HCs) contribute to fracture healing. However, there has been no study investigating the effect of PTH on HCs. We investigated the effect of pulsatile and continuous PTH treatment on human fracture HCs in vitro. HCs were isolated from seven patients. The HCs were divided into four groups: growth medium; control [osteogenic medium (OM) without PTH]; PTH-C (OM with continuous PTH); and PTH-P (OM with pulsatile PTH) groups. Osteogenic differentiation potential and proliferation of HCs were compared among the four groups. For chondrogenesis, the HCs were divided into two groups: control [chondrogenic medium (CM) without PTH]; and PTH-C (CM with continuous PTH) groups, and chondrogenic differentiation potential was analysed. PTH treatment did not affect cell proliferation, regardless of the mode of administration. Osteogenic activity was also not significantly affected by continuous PTH treatment but significantly inhibited by pulsatile PTH treatment. Conversely, chondrogenic differentiation was significantly inhibited by continuous PTH treatment. Our results revealed that PTH treatment on HCs, either continuous or pulsatile, does not exhibit any positive effect, and indicates that exogenous PTH administration after fracture has no effect on HCs. PTH may not have a positive effect at the fracture site during the early stage of fracture healing in which haematoma formation occurs. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of low-intensity pulsed ultrasound on bone morphogenetic protein 7-induced osteogenic differentiation of human nonunion tissue-derived cells in vitro

OBJECTIVES

Low-intensity pulsed ultrasound (US) has been shown to have positive effects on the healing of nonunions, and bone morphogenetic protein 7 (BMP-7) is known to be a strong stimulator of osteogenic differentiation. Recently, we showed that nonunion tissue contains multilineage mesenchymal progenitor cells, suggesting that nonunion tissue-derived cells may play an important role during the healing process of nonunions. In this study, we investigated whether low-intensity pulsed US promoted BMP-7-induced osteogenic differentiation of nonunion tissue-derived cells in vitro.

METHODS

Nonunion tissue-derived cells were isolated from 7 patients. The cells were divided into two groups: (1) BMP-7 alone, consisting of nonunion tissue-derived cells cultured in osteogenic medium containing BMP-7 without low-intensity pulsed US treatment; and (2) BMP-7 + low-intensity pulsed US, consisting of nonunion tissue-derived cells cultured in osteogenic medium containing BMP-7 with low-intensity pulsed US treatment. The osteogenic differentiation potential and proliferation of nonunion tissue-derived cells were compared between the two groups.

RESULTS

The alkaline phosphatase activity, gene expression levels of alkaline phosphatase and runt-related transcription factor 2, and mineralization were higher in the BMP-7 + low-intensity pulsed US group than in the BMP-7-alone group. There was no significant difference in cell proliferation between the two groups.

CONCLUSIONS

These findings show a significant effect of low-intensity pulsed US on the osteogenic differentiation of nonunion tissue-derived cells induced by BMP-7. This study may provide substantial evidence for the clinical combined application of BMP-7 and low-intensity pulsed US for nonunion treatment.