Osteoblasts stimulated with pulsed electromagnetic fields increase HUVEC proliferation via a VEGF-A independent mechanism

Signalling pathways underlying pulsed electromagnetic fields in bone repair

Pulsed electromagnetic field (PEMF) stimulation is a prospective non-invasive and safe physical therapy strategy for accelerating bone repair. PEMFs can activate signalling pathways, modulate ion channels, and regulate the expression of bone-related genes to enhance osteoblast activity and promote the regeneration of neural and vascular tissues, thereby accelerating bone formation during bone repair. Although their mechanisms of action remain unclear, recent studies provide ample evidence of the effects of PEMF on bone repair. In this review, we present the progress of research exploring the effects of PEMF on bone repair and systematically elucidate the mechanisms involved in PEMF-induced bone repair. Additionally, the potential clinical significance of PEMF therapy in fracture healing is underscored. Thus, this review seeks to provide a sufficient theoretical basis for the application of PEMFs in bone repair.

A novel implant surface modification mode of Fe3O4-containing TiO2 nanorods with sinusoidal electromagnetic field for osteoblastogenesis and angiogenesis

Implants made of Ti and its alloys are widely utilized in orthopaedic surgeries. However, insufficient osseointegration of the implants often causes complications such as aseptic loosening. Our previous research discovered that disordered titanium dioxide nanorods (TNrs) had satisfactory antibacterial properties and biocompatibility, but TNrs harmed angiogenic differentiation, which might retarded the osseointegration process of the implants. Magnetic nanomaterials have a certain potential in promoting osseointegration, electromagnetic fields within a specific frequency and intensity range can facilitate angiogenic and osteogenic differentiation. Therefore, this study used Fe₃O₄ to endow magnetism to TNrs and explored the regulation effects of Ti, TNrs, and Fe₃O₄-TNrs under 1 ​mT 15 ​Hz sinusoidal electromagnetic field (SEMF) on osteoblastogenesis, osseointegration, angiogenesis, and its mechanism. We discovered that after the addition of SEMF treatment to VR-EPCs cultured on Fe₃O₄-TNrs, the calcineurin/NFAT signaling pathway was activated, which then reversed the inhibitory effect of Fe₃O₄-TNrs on angiogenesis. Besides, Fe₃O₄-TNrs with SEMF enhanced osteogenic differentiation and osseointegration. Therefore, the implant modification mode of Fe₃O₄-TNrs with the addition of SEMF could more comprehensively promote osseointegration and provided a new idea for the modification of implants.

The Effect of Different Frequencies of Pulsed Electromagnetic Fields on Cartilage Repair of Adipose Mesenchymal Stem Cell-Derived Exosomes in Osteoarthritis

BACKGROUND

The intra-articular injection of mesenchymal stem cell (MSC)-derived exosomes has already been proved to reverse osteoarthritic cartilage degeneration. Pulsed electromagnetic field (PEMF) has been found to regulate the biogenic function of MSCs. However, the effect of PEMF on MSC-derived exosomes has not yet been characterized. The aim of this study was to elucidate the regulatory role of different frequencies of PEMF in promoting the osteoarthritic cartilage regeneration of MSC-derived exosomes.

METHODS

The adipose tissue-derived MSCs (AMSCs) were extracted from the epididymal fat of healthy rats and further exposed to the PEMF at 1 mT amplitude and a frequency of 15, 45, and 75 Hz, respectively, in an incubator. The chondrocytes were treated with interlukin-1β (IL-1β) and the regenerative effect of co-culturing with PEMF-exposed AMSC-derived exosomes was assessed via Western blot, quantitative polymerase chain reaction, and ELISA assays. A rat model of osteoarthritis was established by anterior cruciate ligament transection (ACLT) surgery and received 4 times intra-articular injection of PEMF-exposed AMSC-derived exosomes once a week. After 8 weeks, the knee joint specimens of rats were collected for micro-computed tomography and histologic analyses.

RESULTS

PEMF-exposed AMSC-derived exosomes could be endocytosed with IL-1β-induced chondrocytes. Compared with the AMSC-derived exosomes alone, the PEMF-exposed AMSC-derived exosomes substantially suppressed the inflammation and extracellular matrix degeneration of IL-1β-induced chondrocytes as shown by higher expression of transcripts and proteins of COL2A1, SOX9, and ACAN and lower expression of MMP13 and caspase-1. Of these, the 75-Hz PEMF presented a more significant inhibitive effect than the 15-Hz and 45-Hz PEMFs. Furthermore, the intra-articular injection of 75-Hz PEMF-exposed exosomes could obviously increase the number of tibial epiphyseal trabeculae, lead to a remarkable decrease in Osteoarthritis Research Society International score, and upregulate the COL2A1 and ACAN protein level of the degenerated cartilage.

CONCLUSION

The present study demonstrated that PEMF stimulation could effectively promote the regeneration effects of AMSC-derived exosomes on osteoarthritic cartilage. Compared with other frequency parameters, the PEMF at a frequency of 75 Hz showed a superior positive effect on AMSC-derived exosomes in suppressing the IL-1β-induced chondrocyte inflammation and extracellular matrix catabolism, as well as the osteoarthritic cartilage degeneration.

Coupling induction of osteogenesis and type H vessels by pulsed electromagnetic fields in ovariectomy-induced osteoporosis in mice

The growth of blood vessels and osteogenesis are coupled in bone tissue. A specialized subset of CD31^hiEndomucin^hi (CD31^hiEmcn^hi) vascular endothelium in bone has been identified to positively regulate bone formation. Pulsed electromagnetic field (PEMF) can promote the facture healing and reverse the loss of bone mass. However, the underlying mechanisms mediating in the positive effects of PEMF on bone mass accrual remain unclear. In the ovariectomized (OVX) osteoporotic mouse model, PEMF with specific parameters was administrated after 12 weeks of surgery and continued for 8 weeks. μCT analysis, quantitative PCR and Elisa assays were used to assess the PEMF-induced the osteogenesis, while immunostaining and flow cytometry were used to evaluate the abundance of CD31^hiEmcn^hi endothelium in the metaphysis near the growth plate. Administration of PEMF substantially countered OVX-induced bone loss as shown by greater trabecular bone, higher expression of Osterix, PDGFB and Col-1a1 transcripts, and modulation of bone anabolic and catabolic activity. The PEMF-induced osteogenesis was coupled by the expansion of CD31^hiEmcn^hi endothelium as demonstrated by CD31 and Endomucin double-positive immunostaining and flow cytometry. Concurrently, the higher level of HIF-α was found in PEMF-treated mice than in vehicle controls. Notably, inhibition of HIF-1α considerably reduced PEMF-induced osteogenesis, and led to a remarkable decrease of CD31^hiEmcn^hi vessels in the PEMF-treated OVX mice. The present study demonstrated the PEMF-induced coupling promotion of osteogenesis and CD31^hiEmcn^hi endothelial cells in a mouse model of postmenopausal osteoporosis. This coupling effect might be mediated in HIF-1α signaling in CD31^hiEmcn^hi endothelium. These findings open up new directions of al that might enable therapeutic improvement of osteogenesis in patients with osteoporosis.

Quantitative Magnetic Resonance Imaging of Femoral Head Articular Cartilage Change in Patients with Hip Osteonecrosis Treated with Extracorporeal Shock Wave Therapy

BACKGROUND

Multiple reports have demonstrated the therapeutic potential of extracorporeal shock wave (ESWT) in osteonecrosis of the femoral head (ONFH). However, few studies reported the changes in hip articular cartilage after the intervention. This study aimed to investigate the effect of ESWT on femoral head cartilage using a novel technique, quantitative T2-mapping magnetic resonance imaging.

METHODS

A total of 143 eligible patients with unilateral early-stage ONFH were randomized into the ESWT group and control group. Seventy-three patients in the ESWT group received two sessions of ESWT with oral drug treatment, while seventy patients in the control group received oral drug treatment only. The visual analog pain scale (VAS) and Harris hip score (HHS) at 3-month, 6-month, and 12-month follow-up were used as the clinical evaluation index. The radiological evaluation index used the T2 mapping values, necrotic size, and China-Japan Friendship Hospital (CJFH) classification.

RESULTS

A total of 143 patients (62 females and 81 males) were finally included, and the characteristics before treatment were comparable between the two groups. At the last follow-up (12 months), the T2 values and ΔT2 changes in the ESWT group were all smaller than those in the control group (p=0.042; p=0.039), while the CJFH classification of ONFH and necrotic lesion size were not statistically significant. At 3 months and 6 months, the VAS in the ESWT group was lower than that in the control group (p=0.021; p=0.046) and the HHS in the ESWT group was higher (p=0.028; p=0.039). However, there were no significant differences in the VAS and HHS at 12 months between the ESWT and control groups.

CONCLUSIONS

The results of the current study indicated that, based on drug treatment, ESWT is an effective treatment method for nontraumatic ONFH, which could result in significant pain relief and function restoration. Furthermore, it could delay the injury of femoral head cartilage during the progression of ONFH.

[Pathophysiological mechanisms of the therapeutic action of alternating electromagnetic fields in the treatment of osteoarticular pathology]

Treatment of osteoarticular pathology with an alternating electromagnetic field (AEMF) is used today as a promising, non-invasive and safe strategy of physiotherapy. It has been shown that the action of alternating electromagnetic fields on the musculoskeletal system triggers signaling cascades that effectively contribute to the restoration of bone and articular tissue. The pathophysiological mechanisms underlying the cellular and subcellular effects of stimulation by an alternating electromagnetic field during the restoration of bone and articular tissue are considered. It was pointed out the several key signaling pathways involved in the restoration of bone and articular tissue under the influence of electromagnetic fields with an analysis of the potential for therapeutic application of electromagnetic fields alone or in combination with other available therapies.

Pulsed Electromagnetic Field Stimulation of Bone Healing and Joint Preservation: Cellular Mechanisms of Skeletal Response

The US FDA has approved pulsed electromagnetic fields (PEMFs) as a safe and effective treatment for nonunions of bone. Despite its clinical use, the mechanisms of action of electromagnetic stimulation of the skeleton have been elusive. Recently, cell membrane receptors have been identified as the site of action of PEMF and provide a mechanistic rationale for clinical use. This review highlights key processes in cell responses to PEMF as follows: (1) signal transduction through A_2A and A₃ adenosine cell membrane receptors and (2) dose-response effects on the synthesis of structural and signaling extracellular matrix (ECM) components. Through these actions, PEMF can increase the structural integrity of bone and cartilage ECM, enhancing repair, and alter the homeostatic balance of signaling cytokines, producing anti-inflammatory effects. PEMFs exert a proanabolic effect on the bone and cartilage matrix and a chondroprotective effect counteracting the catabolic effects of inflammation in the joint environment. Understanding of PEMF membrane targets, and of the specific intracellular pathways involved, culminating in the synthesis of ECM proteins and reduction in inflammatory cytokines, should enhance confidence in the clinical use of PEMF and the identification of clinical conditions likely to be affected by PEMF exposure.

Emerging medical applications based on non-ionizing electromagnetic fields from 0 Hz to 10 THz

The potential for using non-ionizing electromagnetic fields (EMF; at frequencies from 0 Hz up to the THz range) for medical purposes has been of interest since many decades. A number of established and familiar methods are in use all over the world. This review, however, provides an overview of applications that already play some clinical role or are in earlier stages of development. The covered methods include modalities used for bone healing, cancer treatment, neurological conditions, and diathermy. In addition, certain other potential clinical areas are touched upon. Most of the reviewed technologies deal with therapy, whereas just a few diagnostic approaches are mentioned. None of the discussed methods are having such a strong impact in their field of use that they would be expected to replace conventional methods. Partly this is due to a knowledge base that lacks mechanistic explanations for EMF effects at low-intensity levels, which often are used in the applications. Thus, the possible optimal use of EMF approaches is restricted. Other reasons for the limited impact include a scarcity of well-performed randomized clinical trials that convincingly show the efficacy of the methods and that standardized user protocols are mostly lacking. Presently, it seems that some EMF-based methods can have a niche role in treatment and diagnostics of certain conditions, mostly as a complement to or in combination with other, more established, methods. Further development and a stronger impact of these technologies need a better understanding of the interaction mechanisms between EMF and biological systems at lower intensity levels. The importance of the different physical parameters of the EMF exposure needs also further investigations.

The cellular effects of Pulsed Electromagnetic Fields on osteoblasts: A review

Electromagnetic fields (EMFs) have long been known to interact with living organisms and their cells and to bear the potential for therapeutic use. Among the most extensively investigated applications, the use of Pulsed EMFs (PEMFs) has proven effective to ameliorate bone healing in several studies, although the evidence is still inconclusive. This is due in part to our still-poor understanding of the mechanisms by which PEMFs act on cells and affect their functions and to an ongoing lack of consensus on the most effective parameters for specific clinical applications. The present review has compared in vitro studies on PEMFs on different osteoblast models, which elucidate potential mechanisms of action for PEMFs, up to the most recent insights into the role of primary cilia, and highlight the critical issues underlying at least some of the inconsistent results in the available literature. Bioelectromagnetics. 2019;9999:XX-XX. © 2019 Bioelectromagnetics Society.

The Use of Pulsed Electromagnetic Fields to Promote Bone Responses to Biomaterials In Vitro and In Vivo

Implantable biomaterials are extensively used to promote bone regeneration or support endosseous prosthesis in orthopedics and dentistry. Their use, however, would benefit from additional strategies to improve bone responses. Pulsed Electromagnetic Fields (PEMFs) have long been known to act on osteoblasts and bone, affecting their metabolism, in spite of our poor understanding of the underlying mechanisms. Hence, we have the hypothesis that PEMFs may also ameliorate cell responses to biomaterials, improving their growth, differentiation, and the expression of a mature phenotype and therefore increasing the tissue integration of the implanted devices and their clinical success. A broad range of settings used for PEMFs stimulation still represents a hurdle to better define treatment protocols and extensive research is needed to overcome this issue. The present review includes studies that investigated the effects of PEMFs on the response of bone cells to different classes of biomaterials and the reports that focused on in vivo investigations of biomaterials implanted in bone.

Low-frequency pulsed electromagnetic field pretreated bone marrow-derived mesenchymal stem cells promote the regeneration of crush-injured rat mental nerve

Bone marrow-derived mesenchymal stem cells (BMSCs) have been shown to promote the regeneration of injured peripheral nerves. Pulsed electromagnetic field (PEMF) reportedly promotes the proliferation and neuronal differentiation of BMSCs. Low-frequency PEMF can induce the neuronal differentiation of BMSCs in the absence of nerve growth factors. This study was designed to investigate the effects of low-frequency PEMF pretreatment on the proliferation and function of BMSCs and the effects of low-frequency PEMF pre-treated BMSCs on the regeneration of injured peripheral nerve using in vitro and in vivo experiments. In in vitro experiments, quantitative DNA analysis was performed to determine the proliferation of BMSCs, and reverse transcription-polymerase chain reaction was performed to detect S100 (Schwann cell marker), glial fibrillary acidic protein (astrocyte marker), and brain-derived neurotrophic factor and nerve growth factor (neurotrophic factors) mRNA expression. In the in vivo experiments, rat models of crush-injured mental nerve established using clamp method were randomly injected with low-frequency PEMF pretreated BMSCs, unpretreated BMSCs or PBS at the injury site (1 × 10⁶ cells). DiI-labeled BMSCs injected at the injury site were counted under the fluorescence microscope to determine cell survival. One or two weeks after cell injection, functional recovery of the injured nerve was assessed using the sensory test with von Frey filaments. Two weeks after cell injection, axonal regeneration was evaluated using histomorphometric analysis and retrograde labeling of trigeminal ganglion neurons. In vitro experiment results revealed that low-frequency PEMF pretreated BMSCs proliferated faster and had greater mRNA expression of growth factors than unpretreated BMSCs. In vivo experiment results revealed that compared with injection of unpretreated BMSCs, injection of low-frequency PEMF pretreated BMSCs led to higher myelinated axon count and axon density and more DiI-labeled neurons in the trigeminal ganglia, contributing to rapider functional recovery of injured mental nerve. These findings suggest that low-frequency PEMF pretreatment is a promising approach to enhance the efficacy of cell therapy for peripheral nerve injury repair.

Schwann-like cells differentiated from human dental pulp stem cells combined with a pulsed electromagnetic field can improve peripheral nerve regeneration

The purpose of this study was to investigate the effect of Schwann-like cells combined with pulsed electromagnetic field (PEMF) on peripheral nerve regeneration. Schwann-like cells were derived from human dental pulp stem cells (hDPSCs) and verified with CD104, S100, glial fibrillary acidic protein (GFAP), laminin, and P75^NTR immunocytochemistry. Gene expression of P75^NTR and S100 were analyzed. Male Sprague-Dawley rats (200-250g, 6-week-old) were divided into seven groups (n = 10 each): control, sham, PEMF, hDPSCs, hDPSCs + PEMF, Schwann-like cells, Schwann-like cells + PEMF. Cells were transplanted (1 × 10⁶ /10µl/rat) at crush-injury site or combined with PEMF (50 Hz, 1 h/day, 1 mT). Nerve regeneration was evaluated with functional test, histomorphometry and retrograde labelled neurons. Schwann-like cells expressed CD104, S100, GFAP, laminin, and p75 neurotrophin receptor (P75^NTR ). P75^NTR and S100 mRNA expression was highest in Schwann-like cells + PEMF group, which also showed increased Difference and Gap scores. Axons and retrograde labeled neurons increased in all treatment groups. Schwann-like cells, hDPSCs with or without PEMF, and PEMF only improved peripheral nerve regeneration. Schwann-like cells + PEMF showed highest regeneration ability; PEMF has additive effect on hDPSCs, Schwann-like cell in vitro and nerve regeneration ability after transplantation in vivo. Bioelectromagnetics. 37:163-174, 2016. © 2016 Wiley Periodicals, Inc.

Intractable bone marrow edema syndrome of the hip

There is a need for an effective and noninvasive treatment for intractable bone marrow edema syndrome of the hip. Forty-six patients with intractable bone marrow edema syndrome of the hip were retrospectively studied to compare the short-term clinical effects of treatment with high-energy extracorporeal shock wave therapy vs femoral head core decompression. The postoperative visual analog scale score decreased significantly more in the extracorporeal shock wave therapy group compared with the femoral head core decompression group (P<.05). For unilateral lesions, postoperative Harris Hip Scores for all hips in the extracorporeal shock wave therapy group were more significantly improved than Harris Hip Scores for all hips in the femoral head core decompression group (P<.05). Patients who underwent extracorporeal shock wave therapy also resumed daily activities significantly earlier. Average overall operative time was similar in both groups. Symptoms disappeared significantly sooner in the extracorporeal shock wave therapy group in patients with both unilateral (P<.01) and bilateral lesions (P<.05). Hospital costs were significantly lower with extracorporeal shock wave therapy compared with femoral head core decompression. The intraoperative fluoroscopy radiation dose was lower in extracorporeal shock wave therapy than in femoral head core decompression for both unilateral (P<.05) and bilateral lesions (P<.01). On magnetic resonance imaging (MRI), bone marrow edema improved in all patients during the follow-up period. After extracorporeal shock wave therapy, all patients remained pain-free and had normal findings on posttreatment radiographs and MRI scans. Extracorporeal shock wave therapy appears to be a valid, reliable, and noninvasive tool for rapidly resolving intractable bone marrow edema syndrome of the hip, and it has a low complication rate and relatively low cost compared with other conservative and surgical treatment approaches.

Regulation of endothelial MAPK/ERK signalling and capillary morphogenesis by low-amplitude electric field

Low-amplitude electric field (EF) is an important component of wound-healing response and can promote vascular tissue repair; however, the mechanisms of action on endothelium remain unclear. We hypothesized that physiological amplitude EF regulates angiogenic response of microvascular endothelial cells via activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway. A custom set-up allowed non-thermal application of EF of high (7.5 GHz) and low (60 Hz) frequency. Cell responses following up to 24 h of EF exposure, including proliferation and apoptosis, capillary morphogenesis, vascular endothelial growth factor (VEGF) expression and MAPK pathways activation were quantified. A db/db mouse model of diabetic wound healing was used for in vivo validation. High-frequency EF enhanced capillary morphogenesis, VEGF release, MEK-cRaf complex formation, MEK and ERK phosphorylation, whereas no MAPK/JNK and MAPK/p38 pathways activation was observed. The endothelial response to EF did not require VEGF binding to VEGFR2 receptor. EF-induced MEK phosphorylation was reversed in the presence of MEK and Ca(2+) inhibitors, reduced by endothelial nitric oxide synthase inhibition, and did not depend on PI3K pathway activation. The results provide evidence for a novel intracellular mechanism for EF regulation of endothelial angiogenic response via frequency-sensitive MAPK/ERK pathway activation, with important implications for EF-based therapies for vascular tissue regeneration.

Extracorporeal shock wave therapy in early osteonecrosis of the femoral head: prospective clinical study with long-term follow-up

INTRODUCTION

Extracorporeal shock wave therapy (ESWT) may exert beneficial effects in avascular necrosis of femoral head (AVNFH).

PATIENTS

The current study evaluated the effectiveness of ESWT in reducing pain and in slowing down the progression of bone damage in 36 patients with unilateral AVNFH of stage Association Research Circulation Osseous (ARCO) I, II and III. At the beginning of the study, 10 hips were classified as stage I, 11 as stage II and 15 as stage III. Each treatment cycle included four sessions, with 2,400 impulses each administered at 0.50 mJ/mm(2), at 48-72 h intervals. Follow-up examinations were scheduled at 3, 6, 12 and then 24 months.

METHOD

Clinical assessments included assessment of pain scores, Harris Hip Scores and Roles and Maudsley score. Plain radiographs and magnetic resonances of the hip were used to evaluate the size of the lesion, the extent of collapse of subchondral bone, and degenerative changes of the hip joint.

RESULTS

Patients from ARCO stage I group and stage II group achieved significantly better results than patients from ARCO stage III group at all follow-up time points (p < 0.005). During the follow-up period, 10 of the 15 stage III ARCO patients received an arthroplasty. ARCO stages I and II lesions were unchanged on radiographs and on magnetic resonance images.

CONCLUSION

ESWT in ARCO stages I and II may help to prevent progression of the area of avascular necrosis and manage pain.

Stimulation of bone formation and fracture healing with pulsed electromagnetic fields: biologic responses and clinical implications

Pulsed electromagnetic fields (PEMF) have been used for several years to supplement bone healing. However, the mode of action of this non-invasive method is still debated and quantification of its effect on fracture healing is widely varied. At cellular and molecular level, PEMF has been advocated to promote the synthesis of extracellular matrix proteins and exert a direct effect on the production of proteins that regulate gene transcription. Electromagnetic fields may also affect several membrane receptors and stimulate osteoblasts to secrete several growth factors such as bone morphogenic proteins 2 and 4 and TGF-beta. They could also accelerate intramedullary angiogenesis and improve the load to failure and stiffness of the bone. Although healing rates have been reported in up to 87 % of delayed unions and non-unions, the efficacy of the method is significantly varied while patient or fracture related variables could not be clearly associated with a successful outcome.

Pulsed radiofrequency energy accelerates wound healing in diabetic mice

BACKGROUND

Impaired healing is a problematic and common complication of chronic wounds. Although pulsed radiofrequency energy has been used in the treatment of chronic wounds with promising efficacy, its mechanism is still poorly characterized. In this study, the authors used a diabetic mouse model to illustrate the action of pulsed radiofrequency energy on cutaneous wounds and set the stage to begin to understand its mechanism.

METHODS

Full-thickness cutaneous wounds were created in diabetic mice (n = 26). The experimental group (n = 13) was subject to pulsed radiofrequency energy treatment two times per day, whereas the sham group (n = 13) was subjected to sham devices. The rate of wound closure was evaluated by digital analysis of surface area of the wound bed, zone of reepithelialization, and rate of contraction. Mice were euthanized on days 7, 10, 22, and 42 and wounds were evaluated qualitatively and quantitatively by hematoxylin and eosin, Masson's trichrome, and Ki-67 assay for cell proliferation.

RESULTS

In the experimental group, the rate of wound closure was significantly accelerated, particularly beyond day 17. Contraction contributed to the wound healing process rather than reepithelialization. This was also associated with increased granulation tissue that was most prominent by day 22 and with enhanced dermal cell proliferation, with 25 percent and 45 percent Ki-67-positive nuclei on days 10 and 22, respectively, as compared with control animals.

CONCLUSION

These results indicate that pulsed radiofrequency energy accelerates impaired wound healing mainly through wound contraction by means of stimulating cell proliferation, granulation tissue formation, and collagen deposition.

Gene expression profile in cultured human umbilical vein endothelial cells exposed to a 300 mT static magnetic field

In a previous investigation we reported that exposure to a moderate (300 mT) static magnetic field (SMF) causes transient DNA damage and promotes mitochondrial biogenesis in human umbilical vein endothelial cells (HUVECs). To better understand the response of HUVECs to the 300 mT SMF, a high-quality subtracted cDNA library representative of genes induced in cells after 4 h of static magnetic exposure was constructed. The global gene expression profile showed that several genes were induced after the SMF exposure. The characterized clones are involved in cell metabolism, energy, cell growth/division, transcription, protein synthesis, destination and storage, membrane injury, DNA damage/repair, and oxidative stress response. Quantitative real-time polymerase chain reaction (qRT-PCR) experiments were performed at 4 and 24 h on four selected genes. Their expression profiles suggest that HUVEC's response to SMF exposure is transient. Furthermore, compared to control cells, an up-regulation of several genes involved in cell growth and division was observed. This up-regulation is likely to be the cause of the slight, but significant, increase in cell proliferation at 12 h post-treatment. These results provide additional support to the notion that SMFs may be harmless to human health, and could support the rationale for their possible use in medical treatments.

In vitro models for the evaluation of angiogenic potential in bone engineering

Blood vessels have a fundamental role both in skeletal homeostasis and in bone repair. Angiogenesis is also important for a successful bone engineering. Therefore, scaffolds should be tested for their ability to favour endothelial cell adhesion, proliferation and functions. The type of endothelial cell to use for in vitro assays should be carefully considered, because the properties of these cells may depend on their source. Morphological and functional relationships between endothelial cells and osteoblasts are evaluated with co-cultures, but this model should still be standardized, particularly for distinguishing the two cell types. Platelet-rich plasma and recombinant growth factors may be useful for stimulating angiogenesis.