Effect of low- and high-intensity pulsed ultrasound on collagen post-translational modifications in MC3T3-E1 osteoblasts

Ultrasound-derived mechanical stimulation of cell-laden collagen hydrogels for bone repair

Cell therapy is emerging as an effective treatment strategy for many diseases. Here we describe a novel approach to bone tissue repair that combines hydrogel-based cell therapy with low intensity pulsed ultrasound (LIPUS), an FDA approved treatment for fracture repair. Bone marrow-derived stromal cells (BMSCs) have been encapsulated in type I collagen hydrogels and mechanically stimulated using LIPUS-derived acoustic radiation force (ARF). We observed the expression and upward trend of load-sensitive, osteoblast-specific markers and determined that the extent of cell response is dependent on an optimal combination of both hydrogel stiffness and ARF intensity. Specifically, cells encapsulated in hydrogels of optimal stiffness respond at the onset of ultrasound by upregulating early bone-sensitive markers such as calcium, cyclooxygenase-2, and prostaglandin E2 , and later by supporting mineralized tissue formation after 21 days of culture. In vivo evaluation of a critical size calvarial defect in NOD scid gamma (NSG) mice indicated that the implantation of BMSC-laden hydrogels of optimal stiffness improved healing of calvarial defects after daily administration of ARF over 4 weeks. Collectively, these findings validate the efficacy of our system of localized cell delivery for treating bone defects where undifferentiated BMSCs are induced to the osteoblastic lineage. Further, in vivo healing may be enhanced via non-invasive transdermal mechanical stimulation of implanted cells using ARF.

Research Progress of Low-Intensity Pulsed Ultrasound in the Repair of Peripheral Nerve Injury

Peripheral nerve injury (PNI) is a common disease that has profound impact on the health of patients, but has poor prognosis. The gold standard for the treatment of peripheral nerve defects is autologous nerve grafting; notwithstanding, due to the extremely high requirement for surgeons and medical facilities, there is great interest in developing better treatment strategies for PNI. Low-intensity pulsed ultrasound (LIPUS) is a noninterventional stimulation method characterized by low-intensity pulsed waves. It has good therapeutic effect on fractures, inflammation, soft tissue regeneration, and nerve regulation, and can participate in PNI repair from multiple perspectives. This review concentrates on the effects and mechanisms of LIPUS in the repair of PNI from the perspective of LIPUS stimulation of neural cells and stem cells, modulation of neurotrophic factors, signaling pathways, proinflammatory cytokines, and nerve-related molecules. In addition, the effects of LIPUS on nerve conduits are reviewed, as nerve conduits are expected to be a successful alternative treatment for PNI with the development of tissue engineering. Overall, the application advantages and prospects of LIPUS in the repair of PNI are highlighted by summarizing the effects of LIPUS on seed cells, neurotrophic factors, and nerve conduits for neural tissue engineering.

Inflammation Responses to Bone Scaffolds under Mechanical Stimuli in Bone Regeneration

Physical stimuli play an important role in one tissue engineering. Mechanical stimuli, such as ultrasound with cyclic loading, are widely used to promote bone osteogenesis; however, the inflammatory response under physical stimuli has not been well studied. In this paper, the signaling pathways related to inflammatory responses in bone tissue engineering are evaluated, and the application of physical stimulation to promote osteogenesis and its related mechanisms are reviewed in detail; in particular, how physical stimulation alleviates inflammatory responses during transplantation when employing a bone scaffolding strategy is discussed. It is concluded that physical stimulation (e.g., ultrasound and cyclic stress) helps to promote osteogenesis while reducing the inflammatory response. In addition, apart from 2D cell culture, more consideration should be given to the mechanical stimuli applied to 3D scaffolds and the effects of different force moduli while evaluating inflammatory responses. This will facilitate the application of physiotherapy in bone tissue engineering.

Effectiveness and Mechanisms of Low-Intensity Pulsed Ultrasound on Osseointegration of Dental Implants and Biological Functions of Bone Marrow Mesenchymal Stem Cells

Dental implant restoration is the preferred choice for patients with dentition defects or edentulous patients, and obtaining stable osseointegration is the determining factor for successful implant healing. The risk of implant failure during the healing stage is still an urgent problem in clinical practice due to differences in bone quality at different implant sites and the impact of some systemic diseases on bone tissue metabolism. Low-intensity pulsed ultrasound (LIPUS) is a noninvasive physical intervention method widely recognized in the treatment of bone fracture and joint damage repair. Moreover, many studies indicated that LIPUS could effectively promote the osseointegration of dental implants and improve the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). This review is aimed at investigating the research progress on the use of LIPUS in dental implant medicine from three aspects: (1) discuss the promoting effects of LIPUS on osseointegration and peri-implant bone regeneration, (2) summarize the effects and associated mechanisms of LIPUS on the biological functions of BMSCs, and (3) introduce the application and prospects of LIPUS in the clinical work of dental implantation. Although many challenges need to be overcome in the future, LIPUS is bound to be an efficient and convenient therapeutic method to improve the dental implantation success rate and expand clinical implant indications.

Effectiveness of low-intensity pulsed ultrasound on osteoarthritis of the temporomandibular joint: A review

Loading is indispensable for the growth, development, and maintenance of joint tissues, including mandibular condylar cartilage, but excessive loading or reduced host adaptive capacity can considerably damage the temporomandibular joint (TMJ), leading to temporomandibular joint osteoarthritis (TMJ-OA). TMJ-OA, associated with other pathological conditions and aging processes, is a highly degenerative disease affecting the articular cartilage. Many treatment modalities for TMJ-OA have been developed. Traditional clinical treatment includes mainly nonsurgical options, such as occlusal splints. However, non-invasive therapy does not achieve joint tissue repair and regeneration. Growing evidence suggests that low-intensity pulsed ultrasound (LIPUS) accelerates bone fracture healing and regeneration, as well as having extraordinary effects in terms of soft tissue repair and regeneration. The latter have received much attention, and various studies have been performed to evaluate the potential role of LIPUS in tissue regeneration including that applied to articular cartilage. The present article provides an overview of the status of LIPUS stimulation used to prevent the onset and progression of TMJ-OA and enhance the tissue regeneration of mandibular condylar cartilage. The etiology and management of TMJ-OA are explained briefly, animal models of TMJ-OA are described, and the effectiveness of LIPUS on cell metabolism and tissue regeneration in the TMJ is discussed.

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.

Acceleration of Bone Defect Healing and Regeneration by Low-Intensity Ultrasound Radiation Force in a Rat Tibial Model

The objective was to evaluate the effect of low-intensity pulsed ultrasound (LIPUS)-induced acoustic radiation force on trabecular bone defect repair and healing in a rat tibial model. A uniform surgical defect, 3.5 mm in diameter, was generated in the proximal bilateral tibial region of rats (N = 20). LIPUS was applied to the defects in the left tibia for 20 min every day for 2 wk. Contralateral defects in the right tibia served as a control without active LIPUS treatment. The micro-computed tomography data revealed that LIPUS-treated tibia exhibited higher bone volume/total volume, connectivity density, trabecular number, and bone mineral density and significantly lower trabecular separation. Histomorphometry analysis indicated a similar trend. Mechanical testing data revealed that LIPUS treatment significantly increased bone stiffness relative to that of the control group. Short-term (2-wk) LIPUS therapy initiated trabecular bone repair and regeneration in large trabecular bone defects, whereas cortical bone remained in the initial non-mineralization stage.

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.

Hydroxyapatite calvaria graft repair in experimental diabetes mellitus in rats

Among the systemic conditions that impact negatively on the planning and execution of surgical procedures, diabetes mellitus (DM) is the primary clinical condition responsible for complications. This study investigated bone formation in critical defects surgically filled with hydroxyapatite (HA) in diabetic rats. A descriptive, randomized sample and blinded analysis were conducted to test bone regeneration in critical bone defects surgically performed in rat calvaria. Twenty adult male Wistar rats were randomly divided into two groups: control, normoglycemic animals (CG); and test, streptozotocin-induced hyperglycemic animals (TG). A circular bone defect was filled with HA and maintained subperiosteally. The clinical parameters evaluated were body weight, water and food intake, fasting blood glucose, and bone alkaline phosphatase. Bone-grafted area samples were submitted for histomorphometric and stereological analysis. The TG showed a significantly higher rate of new bone formation compared with the CG, sacrificed 15 days after surgery (p < 0.0001). However, at the end of the study, there was no significant difference in the amount of bone formed between groups (p = 0.077). In parallel, with the increase in osteoblastic activity observed in the TG by the measurement of systemic bone alkaline phosphatase (p = 0.016), the analysis of polarized microscopy and stereology demonstrated a lower level collagen maturation and mineralization in the TG. Quantitatively, the TG showed significantly better results for bone gain in the first 15 days. Qualitative assessments, however, showed fewer collagen fibers and bone maturation in the TG compared with the CG both at 15 and 45 days. Therefore, the postoperative evaluation of bone grafts with HA in hyperglycemic situations should consider the systemic and local effects of this condition on the quality of bone repair, rather than identifying the filling or stability of the grafted area after the process. We conclude that clinically detectable bone repair in diabetic animal models submitted to hydroxyapatite grafts may be satisfactory in the early stages. However, hyperglycemia compromises the quality of the newly formed bone and the collagen cross-linking involved in this process.

Comparison of the in vitro effects of low-level laser therapy and low-intensity pulsed ultrasound therapy on bony cells and stem cells

To compare the in vitro effectiveness of Low-Level Laser Therapy (LLLT) and Low Intensity Pulsed Ultrasound (LIPUS) on bony cells and related stem cells. In this study, we aim to systematically review the published scientific literature which explores the use of LLLT and LIPUS to biostimulate the activity or the proliferation of bony cells or stem cells in vitro. We searched the database PubMed for LLLT or LIPUS, with/without bone, osteoblast, osteocyte, stem cells, the human osteosarcoma cell line (MG63), bone-forming cells, and cell culture (or in vitro). These studies were subdivided into categories exploring the effect of LLLT or LIPUS on bony cells, stem cells, and other related cells. 75 articles were found between 1987 and 2016; these included: 50 full paper articles on LLLT and 25 full papers on LIPUS. These articles met the eligibility criteria and were included in our review. A detailed and concise description of the LLLT and the LIPUS protocols and their individual effects on bony cells or stem cells and their results are presented in five tables. Based on the main results and the conclusions of the reviewed articles in the current work, both, LLLT and LIPUS, apply a biostimulatory effect on osteoblasts, osteocytes, and enhance osteoblast proliferation and differentiation on different bony cell lines used in in vitro studies, and therefore, these may be useful tools for bone regeneration therapy. Moreover, in consideration of future cell therapy protocols, both, LLLT and LIPUS (especially LLLT), enhnce a significant increase in the initial number of SCs before differentiation, thus increasing the number of differentiated cells for tissue engineering, regenerative medicine, and healing. Further studies are necessary to determine the LLLT or the LIPUS parameters, which are optimal for biostimsulating bony cells and SCs for bone healing and regenerative medicine.

Ultrasound Enhances Dentoalveolar Remodeling in an Ex Vivo Orthodontic, Ovariectomy-Induced Osteoporotic Model

The aim of the study was to investigate the effects of low-intensity pulsed ultrasound (LIPUS) on dentoalveolar structures during application of force to a cultured mandible slice taken from an ovariectomized rat model of osteoporosis. Rats were divided based on whether they had ovariectomy and/or LIPUS application into four groups: control osteoporosis group, control normal group, ultrasound-treated osteoporosis group and ultrasound-treated normal group. The mandibles were dissected, sliced and cultured before application of a 0.5-N force. Tissue specimens from five rats per group received LIPUS; the remaining rats served as untreated controls. Tissue sections were evaluated histologically and histomorphometrically. Osteoporosis significantly affected the alveolar bone without any effect on the dentin-pulp complex. LIPUS enhanced osteoporotic alveolar bone remodeling and increased cementum and predentin thickness. Furthermore, LIPUS application significantly increased odontoblast and periodontal ligament cell counts (p < 0.05) in both groups. Therefore, LIPUS enhances alveolar bone remolding and increases cementum and predentin formation in osteoporotic rat mandible slice organ cultures.

The Role of the Lysyl Oxidases in Tissue Repair and Remodeling: A Concise Review

Tissue injury provokes a series of events containing inflammation, new tissue formation and tissue remodeling which are regulated by the spatially and temporally coordinated organization. It is an evolutionarily conserved, multi-cellular, multi-molecular process via complex signalling network. Tissue injury disorders present grievous clinical problems and are likely to increase since they are generally associated with the prevailing diseases such as diabetes, hypertension and obesity. Although these dynamic responses vary not only for the different types of trauma but also for the different organs, a balancing act between the tissue degradation and tissue synthesis is the same. In this process, the degradation of old extracellular matrix (ECM) elements and new ones' synthesis and deposition play an essential role, especially collagens. Lysyl oxidase (LOX) and four lysyl oxidase-like proteins are a group of enzymes capable of catalyzing cross-linking reaction of collagen and elastin, thus initiating the formation of covalent cross-links that insolubilize ECM proteins. In this way, LOX facilitates ECM stabilization through ECM formation, development, maturation and remodeling. This ability determines its potential role in tissue repair and regeneration. In this review, based on the current in vitro, animal and human in vivo studies which have shown the significant role of the LOXs in tissue repair, e.g., tendon regeneration, ligament healing, cutaneous wound healing, and cartilage remodeling, we focused on the role of the LOXs in inflammation phase, proliferation phase, and tissue remodeling phase of the repair process. By summarizing its healing role, we hope to shed light on the understanding of its potential in tissue repair and provide up to date therapeutic strategies towards related injuries.

Applying low-intensity pulsed ultrasounds (LIPUS) to a zoledronate-associated atypical femoral shaft fracture without cessation of zoledronate therapy for 3 years follow up: a case report

Reports are increasing regarding atypical femoral fractures (AFFs) caused by minor trauma in patients using bisphosphonates (BPs) for long periods. Patients with malignant skeletal metastases potentially are at greater risk for these AFFs, especially considering the high dose and the duration of treatment with BPs. We evaluated a case of atypical femoral shaft fracture treated with an intramedullary nail in a patient treated for five years with zoledronate who had breast cancer with metastases to bone. Although bone union was achieved without cessation of zoledronate therapy by applying low-intensity pulsed ultrasounds (LIPUS), the remodeling phase of the fracture healing process was delayed. For BPs-associated AFFs, LIPUS is an alternative to parathyroid hormone (PTH) analogs such as teriparatide that are contraindicated in patients with malignant skeletal metastases. LIPUS is an effective treatment for fracture healing and may avoid the necessity to discontinue BP therapy.

Ultrasound field characterization and bioeffects in multiwell culture plates

Background

Ultrasound with frequencies in the kilohertz range has been demonstrated to promote biological effects and has been suggested as a non-invasive tool for tissue healing and repair. However, many challenges exist to characterize and develop kilohertz ultrasound for therapy. In particular there is a limited evidence-based guidance and standard procedure in the literature concerning the methodology of exposing biological cells to ultrasound in vitro.

Methods

This study characterized a 45-kHz low-frequency ultrasound at three different preset intensity levels (10, 25, and 75 mW/cm²) and compared this with the thermal and biological effects seen in a 6-well culture setup using murine odontoblast-like cells (MDPC-23). Ultrasound was produced from a commercially available ultrasound-therapy system, and measurements were recorded using a needle hydrophone in a water tank. The transducer was displaced horizontally and vertically from the hydrophone to plot the lateral spread of ultrasound energy. Calculations were performed using Fourier transform and average intensity plotted against distance from the transducer. During ultrasound treatment, cell cultures were directly exposed to ultrasound by submerging the ultrasound transducer into the culture media. Four groups of cell culture samples were treated with ultrasound. Three with ultrasound at an intensity level of 10, 25, and 75 mW/cm², respectively, and the final group underwent a sham treatment with no ultrasound. Cell proliferation and viability were analyzed from each group 8 days after three ultrasound treatments, each separated by 48 h.

Results

The ultrasonic output demonstrated considerable lateral spread of the ultrasound field from the exposed well toward the adjacent culture wells in the multiwell culture plate; this correlated well with the dose-dependent increase in the number of cultured cells where significant biological effects were also seen in adjacent untreated wells. Significant thermal variations were not detected in adjacent untreated wells.

Conclusions

This study highlights the pitfalls of using multiwell plates when investigating the biological effect of kilohertz low-frequency ultrasound on adherent cell cultures.

Dynamic acoustic radiation force retains bone structural and mechanical integrity in a functional disuse osteopenia model

Disuse osteopenia and bone loss have been extensively reported in long duration space mission and long term bed rest. The pathology of the bone loss is similar to osteoporosis but highly confined to weight bearing bones. The current anabolic and/or anti-resorptive drugs have systemic effects and are costly over extended time, with concerns of long term fracture risk. This study use Low Intensity Pulsed Ultrasound (LIPUS) as a non-invasive acoustic force and anabolic stimulus to countermeasure disuse induced bone loss. Four-month old C57BL/6 mice were randomized into five groups, 1) age-matched (AM), 2) non-suspended sham (NS), 3) non-suspended-LIPUS (NU), 4) suspended sham (SS), and 5) suspended-LIPUS (SU) groups. After four weeks of suspension, μCT analyses showed significant decreases in trabecular bone volume fraction (BV/TV) (-36%, p<0.005), bone tissue mineral density (TMD) (-3%, p<0.05), trabecular thickness (Tb.Th) (-12.5%, p<0.005), and increase in bone surface/bone volume (+BS/BV) (+16%, p<0.005), relative to age-matched (AM). The application of LIPUS for 20 min/day for 5 days/week, significantly increased TMD (+3%, p<0.05), Tb.Th (+6%, p<0.05), and decreased BS/BV (-10%, p<0.005), relative to suspension alone (SS) mice. Histomorphometry analyses showed a breakdown of bone microstructure under disuse conditions consist with μCT results. In comparison to SS mice, LIPUS treated bone showed increased structural integrity with increased bone formation rates at metaphysical endosteal and trabecular surfaces (+0.104±0.07 vs 0.031±0.30 μm(3)/μm(2)/day) relative to SS. Four-point bending mechanical tests of disused SS femurs showed reduced elastic modulus (-53%, p<0.05), yield (-33%, p<0.05) and ultimate strength (-45%, p<0.05) at the femoral diaphysis relative to AM bone. LIPUS stimulation mitigated the adverse effects of disuse on bone elastic modulus (+42%, p<0.05), yield strength (+29%, p<0.05), and ultimate strength (+39%, p<0.05) relative to SS femurs. LIPUS provides the essential mechanical stimulus to retain bone morphological and mechanical integrity in disuse conditions. This study demonstrates LIPUS potential as regional therapeutic agent to countermeasure disuse induced bone loss while maintaining bone's integrity.

Low-intensity pulsed ultrasound in dentofacial tissue engineering

Oral and maxillofacial diseases affect millions of people worldwide and hence tissue engineering can be considered an interesting and clinically relevant approach to regenerate orofacial tissues after being affected by different diseases. Among several innovations for tissue regeneration, low-intensity pulsed ultrasound (LIPUS) has been used extensively in medicine as a therapeutic, operative, and diagnostic tool. LIPUS is accepted to promote bone fracture repair and regeneration. Furthermore, the effect of LIPUS on soft tissues regeneration has been paid much attention, and many studies have performed to evaluate the potential use of LIPUS to tissue engineering soft tissues. The present article provides an overview about the status of LIPUS stimulation as a tool to be used to enhance regeneration/tissue engineering. This review consists of five parts. Part 1 is a brief introduction of the acoustic description of LIPUS and mechanical action. In Part 2, biological problems in dentofacial tissue engineering are proposed. Part 3 explores biologic mechanisms of LIPUS to cells and tissues in living body. In Part 4, the effectiveness of LIPUS on cell metabolism and tissue regeneration in dentistry are summarized. Finally, Part 5 relates the possibility of clinical application of LIPUS in orthodontics. The present review brings out better understanding of the bioeffect of LIPUS therapy on orofacial tissues which is essential to the successful integration of management remedies for tissue regeneration/engineering. To develop an evidence-based approach to clinical management and treatment of orofacial degenerative diseases using LIPUS, we would like to be in full pursuit of LIPUS biotherapy. Still, there are many challenges for this relatively new strategy, but the up to date achievements using it promises to go far beyond the present possibilities.

Diabetes, collagen, and bone quality

Diabetes increases risk of fracture, although type 2 diabetes is characterized by normal or high bone mineral density (BMD) compared with the patients without diabetes. The fracture risk of type 1 diabetes as well as type 2 diabetes increases beyond an explained by a decrease of BMD. Thus, diabetes may reduce bone strength without change in BMD. Whole bone strength is determined by bone density, structure, and quality, which encompass the micro-structural and tissue material properties. Recent literature showed that diabetes reduces bone material properties rather than BMD. Collagen intermolecular cross-linking plays an important role in the expression of bone strength. Collagen cross-links can be divided into beneficial enzymatic immature divalent and mature trivalent cross-links and disadvantageous nonenzymatic cross-links (Advanced glycation end products: AGEs) induced by glycation and oxidation. The formation pathway and biological function are quite different. Not only hyperglycemia, but also oxidative stress induces the reduction in enzymatic cross-links and the formation of AGEs. In this review, we describe the mechanism of low bone quality in diabetes and the usefulness of the measurement of plasma or urinary level of AGEs for estimation of fracture risk.

Insight concerning the mechanism of therapeutic ultrasound facilitating gene delivery: increasing cell membrane permeability or interfering with intracellular pathways?

Nonviral gene delivery methods encounter major barriers in plasmid DNA (pDNA) trafficking toward the nucleus. The present study aims to understand the role and contribution of therapeutic ultrasound (TUS), if any, in pDNA trafficking in primary cells such as fibroblasts and cell lines (e.g., baby hamster kidney [BHK]) during the transfection process. Using compounds that alter the endocytic pathways and the cytoskeletal network, we show that after TUS application, pDNA trafficking in the cytoplasm is not mediated by endocytosis or by the cytoskeletal network. Transfection studies and confocal analyses showed that the actin fibers impeded TUS-mediated transfection in BHK cells, but not in fibroblasts. Flow cytometric analyses indicated that pDNA uptake by cells occurs primarily when the pDNA is added before and not after TUS application. Taken together, these results suggest that TUS by itself operates as a mechanical force driving the pDNA through the cell membrane, traversing the cytoplasmic network and into the nucleus.

Osteogenic differentiation of human adipose-derived stem cells can be accelerated by controlling the frequency of continuous ultrasound

OBJECTIVES

The purpose of this study was to demonstrate that the effects of continuous ultrasound on the osteogenic differentiation of human adipose-derived stem cells (hASCs) are dependent on the frequency in vitro.

METHODS

Before stimulation, we characterized the hASCs using cluster of differentiation marker profiles and tridifferentiation. Then we selected effective frequencies in the range of 0.5 to 1.5 MHz (with a peak negative pressure of 52 kPa), which upregulated runt-related transcription factor 2 messenger RNA expression. Next, the effects of ultrasound at the selected frequencies on the osteogenic differentiation were evaluated at the protein level. Alkaline phosphatase activity and the formation of mineralized nodules were measured. We additionally identified the cellular mechanisms underlying the effects of ultrasound stimulation using Western blotting.

RESULTS

The hASCs showed general cluster of differentiation marker profiles of stem cells and confirmed their potentials to yield adipogenic, chondrogenic, and osteogenic differentiation. Frequencies of 0.5, 1.0, and 1.5 MHz were selected for higher runt-related transcription factor 2 expression in the range of 0.5 to 1.5 MHz. Among the 3 groups, alkaline phosphatase activity and the formation of mineralized nodules were increased in cells exposed to 1.5-MHz ultrasound compared with cells exposed to 0.5-or 1.0-MHz ultrasound and nontreated control cells. We additionally confirmed that this acceleration of osteogenic differentiation was related to p38 and protein kinase B signaling pathways.

CONCLUSIONS

In this study, we found that, in the selected range, 1.5 MHz was the most effective frequency for inducing the osteogenic differentiation of hASCs.

Bone quality in diabetes

Diabetes is associated with increased risk of fracture, although type 2 diabetes is characterized by normal bone mineral density (BMD). The fracture risk of type 1 diabetes increases beyond an explained by a decrease of BMD. Thus, diabetes may be associated with a reduction of bone strength that is not reflected in the measurement of BMD. Based on the present definition, both bone density and quality, which encompass the structural and material properties of bone, are important factors in the determination of bone strength. Diabetes reduces bone quality rather than BMD. Collagen cross-linking plays an important role in bone strength. Collagen cross-links can be divided into lysyl hydroxylase and lysyl oxidase-mediated enzymatic immature divalent cross-links, mature trivalent cross-links, and glycation- or oxidation-induced non-enzymatic cross-links (Advanced Glycation End-products: AGEs) such as pentosidine. These types of cross-links differ in the mechanism of formation and in function. Not only hyperglycemia, but also oxidative stress induces the reduction in enzymatic beneficial cross-links and the accumulation of disadvantageous AGEs in bone. In this review, we describe the mechanism of low bone quality in diabetes.

Current status of low intensity pulsed ultrasound for dental purposes

Over the past few years, tissue engineering applied to the dental field has achieved relevant results. Tissue engineering can be described by actions taken to improve biological functions. Several methods have been described to enhance cellular performance and low intensity pulsed ultrasound (LIPUS) has shown to play an important role in cell metabolism. The present article provides an overview about the current status of LIPUS as a tissue engineering tool to be used to enhance tooth and periodontal regeneration.

How linear tension converts to curvature: geometric control of bone tissue growth

This study investigated how substrate geometry influences in-vitro tissue formation at length scales much larger than a single cell. Two-millimetre thick hydroxyapatite plates containing circular pores and semi-circular channels of 0.5 mm radius, mimicking osteons and hemi-osteons respectively, were incubated with MC3T3-E1 cells for 4 weeks. The amount and shape of the tissue formed in the pores, as measured using phase contrast microscopy, depended on the substrate geometry. It was further demonstrated, using a simple geometric model, that the observed curvature-controlled growth can be derived from the assembly of tensile elements on a curved substrate. These tensile elements are cells anchored on distant points of the curved surface, thus creating an actin “chord” by generating tension between the adhesion sites. Such a chord model was used to link the shape of the substrate to cell organisation and tissue patterning. In a pore with a circular cross-section, tissue growth increases the average curvature of the surface, whereas a semi-circular channel tends to be flattened out. Thereby, a single mechanism could describe new tissue growth in both cortical and trabecular bone after resorption due to remodelling. These similarities between in-vitro and in-vivo patterns suggest geometry as an important signal for bone remodelling.

Effects of combined mechanical stimulation on the proliferation and differentiation of pre-osteoblasts

We observed how combined mechanical stimuli affect the proliferation and differentiation of pre-osteoblasts. For this research, a bioreactor system was developed that can simultaneously stimulate cells with cyclic strain and ultrasound, each of which is known to effectively stimulate bone tissue regeneration. MC3T3-E1 pre-osteoblasts were chosen for bone tissue engineering due to their osteoblast-like characteristics. 3-D scaffolds were fabricated with polycaprolactone and poly-L-lactic acid using the salt leaching method. The cells were stimulated by the bioreactor with cyclic strain and ultrasound. The bioreactor was set at a frequency of 1.0 Hz and 10 % strain for cyclic strain and 1.0 MHz and 30 mW/cm(2) for ultrasound. Three experimental groups (ultrasound, cyclic strain, and combined stimulation) and a control group were examined. Each group was stimulated for 20 min/day. Mechanical stimuli did not affect MC3T3-E1 cell proliferation significantly up to 10 days when measured with the cell counting kit-8. However, gene expression analysis of collagen type-I, osteocalcin, RUNX2, and osterix revealed that the combined mechanical stimulation accelerated the matrix maturation of MC3T3-E1 cells. These results indicate that the combined mechanical stimulation can enhance the differentiation of pre-osteoblasts more efficiently than simple stimuli, in spite of no effect on cell proliferation.

Mitigation of bone loss with ultrasound induced dynamic mechanical signals in an OVX induced rat model of osteopenia

This study tests the hypothesis that an ultrasound generated dynamic mechanical signal can attenuate bone loss in an estrogen deficient model of osteopenia. Eighty-four 16-week-old Sprague-Dawley rats were divided into six groups: baseline control, age-matched control, ovariectomy (OVX) control, OVX+5mW/cm(2) ultrasound (US), OVX+30mW/cm(2) US and OVX+100mW/cm(2) US. Low intensity pulsed ultrasound (LIPUS) was delivered transdermally at the L4/L5 vertebrae, using gel-coupled plane wave US transducers. The signal, characterized by 200μs pulses of 1.5MHz sine waves repeating at 1kHz with spatial-averaged temporal-averaged (SATA) intensities of 5, 30 or 100mW/cm(2), was applied 20 min/day, 5 days/week for 4 weeks. OVX treatment reduced bone volume fraction 40% and compromised microstructure at 4 weeks. LIPUS treatment, however, significantly increased BV/TV (+33%) compared to OVX controls for the 100mW/cm(2) treated group. SMI and Tb.N showed significant improvements compared with OVX for the 100mW/cm(2) treated group and Tb.Th was significantly improved in the 30 and 100mW/cm(2) treated groups. Improvements in bone's microstructural characteristics with 100mW/cm(2) US treatment translated into improved load bearing characteristics, including a significant 42% increase in apparent level elastic modulus compared to OVX controls. Significant improvement of trabecular mechanical strength was also observed in the treated animals, e.g., principal compressive stress (represent bone's ability to resist loads) was significantly higher compared to OVX controls. Histomorphometric analysis also showed that treatment with 100mW/cm(2) US resulted in a 76% improvement in MS/BS. In addition, measures of bone quantity and quality at the femoral metaphysis suggest that LIPUS is site specific. This study indicates that localized ultrasound treatment, delivered at specific intensities, has beneficial effects on intact bone and may represent a novel intervention for bone loss.

Osteogenic differentiation of rat bone marrow stromal cells by various intensities of low-intensity pulsed ultrasound

Bone growth and repair are under the control of biochemical and mechanical signals. Low-intensity pulsed ultrasound (LIPUS) stimulation at 30mW/cm(2) is an established, widely used and FDA approved intervention for accelerating bone healing in fractures and non-unions. Although this LIPUS signal accelerates mineralization and bone regeneration, the actual intensity experienced by the cells at the target site might be lower, due to the possible attenuation caused by the overlying soft tissue. The aim of this study was to investigate whether LIPUS intensities below 30mW/cm(2) are able to provoke phenotypic responses in bone cells. Rat bone marrow stromal cells were cultured under defined conditions and the effect of 2, 15, 30mW/cm(2) and sham treatments were studied at early (cell activation), middle (differentiation into osteogenic cells) and late (biological mineralization) stages of osteogenic differentiation. We observed that not only 30mW/cm(2) but also 2 and 15mW/cm(2), modulated ERK1/2 and p38 intracellular signaling pathways as compared to the sham treatment. After 5 days with daily treatments of 2, 15 and 30mW/cm(2), alkaline phosphatase activity, an early indicator of osteoblast differentiation, increased by 79%, 147% and 209%, respectively, compared to sham, indicating that various intensities of LIPUS were able to initiate osteogenic differentiation. While all LIPUS treatments showed higher mineralization, interestingly, the highest increase of 225% was observed in cells treated with 2mW/cm(2). As the intensity increased to 15 and 30mW/cm(2), the increase in the level of mineralization dropped to 120% and 82%. Our data show that LIPUS intensities lower than the current clinical standard have a positive effect on osteogenic differentiation of rat bone marrow stromal cells. Although Exogen™ at 30mW/cm(2) continues to be effective and should be used as a clinical therapy for fracture healing, if confirmed in vivo, the increased mineralization at lower intensities might be the first step towards redefining the most effective LIPUS intensity for clinical use.

Low-Intensity Amplitude Modulated Ultrasound Increases Osteoblastic Mineralization

The purpose of this study was to assess the effect of pulsed amplitude modulated ultrasound (pAMUS) on the level of mineralization in osteoblast cell in comparison to cells stimulated with low-intensity pulsed ultrasound (LIPUS). To make the ultrasound effects more enhanced and targeted at region of interest, this study uses a novel approach of applying pulsed amplitude modulated ultrasound to osteoblast cells. The pAMUS signal was generated using two signal generators. Pulsed signal was amplified through a power amplifier and drove two identical focused ultrasound probes, focusing at the same point in the culture dish. The effects of pAMUS were evaluated using a pAMUS signal of 45 kHz and 100 kHz with 20% duty cycle. The hydrophone verified the formation of a focal point at equal distances (16 mm) from the surface of both transducers. Intensity profile using computer controlled 2D scanner showed circular focal point with a diameter of approximately 10 mm. The effect of the signal was studied using MC3T3-E1 cells cultured in osteogenic medium at time points Day 7, 12 and 18. The cells were analyzed for ALP activity and calcium mineralization. The pAMUS significantly increased the ALP activity and matrix calcification in comparison with LIPUS stimulated cultures.

Ultrasound stimulation induces PGE(2) synthesis promoting cementoblastic differentiation through EP2/EP4 receptor pathway

The present study aims to provide insights into how ultrasound treatment (US) can affect the regenerative response of cementum by evaluating the role of prostaglandin E(2) induced by ultrasound stimulation on cementoblastic differentiation. The mouse cementoblast cell line OCCM-30 was exposed to low-intensity ultrasound and the cyclooxygenase-2 (COX-2) mRNA expression and prostaglandin E(2) (PGE(2)) production were quantified. The role of the US-induced PGE(2) in mineralization was examined using COX-2 inhibitor and prostaglandin receptors (EP-receptors) agonists and antagonists. In addition, gene expression of differentiation markers related to mineral metabolism was evaluated. Ultrasound significantly enhanced COX-2 mRNA expression and PGE(2) production. PGE(2) induced by US mediated mineral nodule formation, whereas COX-2 inhibitor treatment eliminated the enhancement of mineralization induced by US stimulation. Mineral deposition was also inhibited by treatment with EP2 or EP4 antagonist. Moreover, up-regulation of differentiation markers induced by US was suppressed by treatment with COX-2 inhibitor. The present findings provide evidence that US stimulation has a positive effect on mineralization ability of cementoblasts through the activation of EP2/EP4 pathway, suggesting that US can be a promising therapeutic tool for cementum repair.

Collagen cross-links as a determinant of bone quality: a possible explanation for bone fragility in aging, osteoporosis, and diabetes mellitus

Collagen cross-linking, a major post-translational modification of collagen, plays important roles in the biological and biomechanical features of bone. Collagen cross-links can be divided into lysyl hydroxylase and lysyloxidase-mediated enzymatic immature divalent cross-links,mature trivalent pyridinoline and pyrrole cross-links, and glycation- or oxidation-induced non-enzymatic cross-links(advanced glycation end products) such as glucosepane and pentosidine. These types of cross-links differ in the mechanism of formation and in function. Material properties of newly synthesized collagen matrix may differ in tissue maturity and senescence from older matrix in terms of crosslink formation. Additionally, newly synthesized matrix in osteoporotic patients or diabetic patients may not necessarily be as well-made as age-matched healthy subjects. Data have accumulated that collagen cross-link formation affects not only the mineralization process but also microdamage formation. Consequently, collagen cross-linking is thought to affect the mechanical properties of bone. Furthermore,recent basic and clinical investigations of collagen cross-links seem to face a new era. For instance, serum or urine pentosidine levels are now being used to estimate future fracture risk in osteoporosis and diabetes. In this review, we describe age-related changes in collagen cross-links in bone and abnormalities of cross-links in osteoporosis and diabetes that have been reported in the literature.

The science of ultrasound therapy for fracture healing

Fracture healing involves a complex interplay of cellular processes, culminating in bridging of a fracture gap with bone. Fracture healing can be compromised by numerous exogenous and endogenous patient factors, and intense research is currently going on to identify modalities that can increase the likelihood of successful healing. Low-intensity pulsed ultrasound (LIPUS) has been proposed as a modality that may have a benefit for increasing reliable fracture healing as well as perhaps increasing the rate of fracture healing. We conducted a review to establish basic scince evidence of therapeutic role of lipus in fracture healing. An electronic search without language restrictions was accomplished of three databases (PubMed, Embase, Cinahl) for ultrasound-related research in osteocyte and chondrocyte cell culture and in animal fracture models, published from inception of the databases through December, 2008. Studies deemed to be most relevant were included in this review. Multiple in vitro and animal in vivo studies were identified. An extensive body of literature exists which delineates the mechanism of action for ultrasound on cellular and tissue signaling systems that may be related to fracture healing. Research on LIPUS in animal fracture models has demonstrated promising results for acceleration of fracture healing and for promotion of fracture healing in compromised tissue beds. A large body of cellular and animal research exists which reveals that LIPUS may be beneficial for accelerating normal fracture healing or for promoting fracture healing in compromised tissue beds. Further investigation of the effects of LIPUS in human fracture healing is warranted for this promising new therapy.

Low-intensity pulsed ultrasound-promoted bone healing is not entirely cyclooxgenase 2 dependent

OBJECTIVE

The purpose of this study was to investigate whether low-intensity pulsed ultrasound (LIPUS) promotes bone healing through the cyclooxgenase 2 (COX-2) pathway.

METHODS

Each male Sprague Dawley rat (n = 48 total) in the study underwent bilateral drilled hole injury in the proximal tibiae. Then the animals were randomly assigned to 2 groups: a COX-2 inhibitor (COX-2in) group, treated with the selective COX-2 inhibitor rofecoxib (3 mg/kg/d), and a control (CON) group, treated with distilled water. Low-intensity pulsed ultrasound was applied to the injured site of a single limb of each rat for 20 min/d at a consistent intensity (30 mW/cm(2)) and frequency (1.5 MHz). Subsets of animals from both groups were killed after 3, 7, or 14 days of single-limb LIPUS treatment. Tissue sections were subjected to alcian blue staining, and the healing status was quantified according to a scoring system.

RESULTS

After 3 and 7 days, the CON group's LIPUS-treated limbs had significantly higher healing scores than its nontreated limbs and the COX-2in group's LIPUS-treated limbs (P < .05). Interestingly, after the 14-day treatment, the COX-2in group's LIPUS-treated limbs had significantly higher healing scores than its nontreated limbs (P < .05) but showed no difference when compared with the CON group.

CONCLUSIONS

Low-intensity pulsed ultrasound did show accelerative efficacy on bone healing. Selective inhibition of COX-2 could delay but not entirely block the benefits of LIPUS on bone healing. Low-intensity ultrasound treatment could promote bone healing through other, non-COX-2-dependent, pathways.

Collagen maturity, glycation induced-pentosidine, and mineralization are increased following 3-year treatment with incadronate in dogs

Collagen cross-linking is a determinant of bone quality. A three-year treatment of bisphosphonate-incadronate disodium-in beagles increased degree of mineralization, collagen maturity, and pentosidine, a compound with advanced glycation end products. The treatment had no effect on the total amount of enzymatic cross-link formation.

INTRODUCTION

Collagen cross-linking is a determinant of bone quality. Recently, we reported that long-term treatment with bisphosphonate increased microdamage accumulation. The aim of this study was to clarify the effect of a three-year treatment with bisphosphonate on degree of mineralization and immature and mature enzymatic cross-links and non-enzymatic collagen cross-link, pentosidine, in cortical bone in the same dogs.

METHODS

Twenty-nine 1-year-old beagles (15 males, 14 females) were divided into three groups that daily were given vehicle or incadronate at doses of 0.3 or 0.6 mg/kg/day orally for three years. A cortex of a rib was fractionated into low- and high-density portions. The contents of calcium, phosphorus, enzymatic immature and mature cross-links, and the non-enzymatic glycation product pentosidine were determined in each fraction.

RESULTS

Calcium, phosphorus, and pentosidine contents and the ratio of mature to immature cross-links increased significantly with incadronate in a dose-dependent manner, but the total amount of enzymatic cross-links was unchanged. The pentosidine content correlated inversely with cortical activation frequency (p < 0.01).

CONCLUSION

Long-term suppression of bone remodeling by bisphosphonate increases degree of mineralization, collagen maturity, and non-enzymatic cross-linking.

Ultrasound mimics the effect of mechanical loading on bone formation in vivo on rat ulnae

While the effect of ultrasound as an extreme example of low-magnitude high-frequency stimulation has been explored in the response of bone to injury, little is known about its effect on normal bone. This experiment was designed to test the hypothesis that ultrasound exerts a similar influence on bone as mechanical stimulation at a physiological level. Three groups of female Wistar rats were anaesthetised (6 per group). In one group, the left ulna was loaded cyclically in vivo 40 times, repeated on a further 5 occasions on alternate days. In a second group, transcutaneous low-intensity pulsed ultrasound stimulation was applied to the left ulnae for the same duration as the period of loading. In a third group, loading and ultrasound stimulation were applied concurrently. The right ulna served as non-loaded control in each animal. At the end of the experiment after 14 days, both ulnae were removed. Induced bone formation was assessed by measuring the proportion of medial periosteal bone surface with double label (dLS/BS, %) and by calculation of mineral apposition rate (MAR) from the inter-label distance. All three treatments induced a significant periosteal response, increasing dLS/BS values from <10% in control limbs to >80% in treated limbs. Increases in MAR of experimental ulnae versus contralateral control ulnae were 2.9 (+/-0.9), 8.6 (+/-2.4) and 8.7 microm (+/-3.2) for the ultrasound only, ultrasound and load, and load only groups, respectively. The effects of loading plus ultrasound were not significantly different from ultrasound alone. These data suggest that ultrasound is able to induce changes in bone that share at least some features with mechanical loading.

Fracture repair with ultrasound: clinical and cell-based evaluation

Fracture repair continues to be widely investigated, both within the clinical realm and at the fundamental research level, in part due to the fact that 5% to 10% of fractures result in either delayed union or nonunion, depending on the duration of incomplete healing. Beyond the temporal delay in repair, nonunions share the same unifying characteristic: all periosteal and endosteal repair processes have stopped and the fracture will not heal without surgical intervention. A less-invasive alternative method--low-intensity pulsed ultrasound--has shown promise as a treatment for delayed unions and nonunions and as a method to facilitate distraction osteogenesis. In this paper, we summarize the clinical effectiveness of low-intensity pulsed ultrasound with regard to fracture repair, treatment of nonunion, and distraction osteogenesis and we discuss the results of a multitude of published studies that have sought to elucidate the mechanisms behind that effectiveness through research on low-intensity pulsed ultrasound exposure on osteoblasts and osteoblast precursors. When evaluated clinically, low-intensity pulsed ultrasound was shown to enhance bone repair (most commonly noted as a decrease in healing time), although variations in patient population hindered a definitive claim to clinical effectiveness. In vitro cellular evaluation and in vivo studies on animal models have revealed an increase in cell proliferation, protein synthesis, collagen synthesis, membrane permeability, integrin expression, and increased cytosolic Ca(2+) levels as well as other increased indicators of bone repair in response to low-intensity pulsed ultrasound exposure. Many of the cellular responses to low-intensity pulsed ultrasound mirror the cellular responses to fluid-induced shear flow, suggesting a link between the two as one potential mechanism of action. The considerable amount of information that has been revealed about the behavior of osteoblasts under low-intensity pulsed ultrasound exposure suggests that the exact mechanism of action is complex. It is clear, however, that considerable progress is being made toward uncovering these mechanisms, which has served to encourage the use of low-intensity pulsed ultrasound in new applications. It is posited that successful noninvasive treatment strategies such as low-intensity pulsed ultrasound may be combined with other conventional and novel tissue-regeneration strategies to develop new treatments for large-scale bone defects.

Pulsed low intensity ultrasound enhances mineralisation in preosteoblast cells

Pulsed low intensity ultrasound has been shown to be highly efficacious in the treatment of nonunion fractures and in the acceleration of fresh fracture healing. MC3T3-E1 subclone 14 cells were cultured for up to 25 days either with or without a daily treatment with low intensity pulsed ultrasound. It was determined that, on day 10 there was a dramatic increase in alkaline phosphatase and MMP-13 mRNA levels detected in ultrasound-treated cultures compared with untreated controls. The activity of alkaline phosphatase was significantly increased at days 6, 8 and 10. On day 10, the amount of mineralisation within cultures, assessed using alizarin red staining, was significantly increased in ultrasound-treated cultures compared with untreated controls. These results suggest that one of the mechanisms that low intensity pulsed ultrasound has on fracture repair is to enhance the process of endochondral ossification where the soft callus is converted to mineralised hard callus.

Role of collagen enzymatic and glycation induced cross-links as a determinant of bone quality in spontaneously diabetic WBN/Kob rats

INTRODUCTION

Diabetes is associated with an increased risk of fracture, although type 2 diabetes is often characterized by normal bone mineral density (BMD). Enzymatic and glycation-induced non-enzymatic cross-links play important roles in the expression of bone strength. The serum vitamin B6 concentration is lower in patients with diabetes than in healthy controls. The aim our study was to see if spontaneously diabetic WBN/Kob rats in the pre- and post-onset of diabetes would serve as a suitable model for studying the pathogenesis of the susceptibility to fracture in diabetes without the reduction of bone mineral density. Seventy male WBN/Kob rats were obtained at the ages of 1 to 18 months.

METHODS

Seventy normal male Wistar rats were used as the non-diabetic, age-matched control. The contents of enzymatic cross-links (dihydroxylysinonorleucine, hydroxylysinonorleucine, lysinonorleucine, pyridinoline and deoxypyridinoline) and non-enzymatic cross-links (pentosidine) were determined in femoral bone. We also analyzed the serum concentration of vitamin B6 (pyridoxal and pyridoxamine), femoral BMD and a three-point bending test of the femur.

RESULTS

A low level of serum vitamin B6 was associated with a decrease in enzymatic crosslinking in bone during the subclinical diabetes stage. After the onset of diabetes, there was a steady decrease in enzymatic cross-links and a steep increase in pentosidine. Furthermore, impaired bone mechanical properties in the WBN/Kob rats despite the lack of reduction in BMD coincided with impaired enzymatic cross-link formation and increases in glycation-induced pentosidine.

CONCLUSIONS

These results indicate that the alteration of enzymatic and non-enzymatic crosslinking in bone could be important for explaining the variation of fracture susceptibility in diabetes.

Degree of mineralization-related collagen crosslinking in the femoral neck cancellous bone in cases of hip fracture and controls

Based on the present definition of osteoporosis, both bone density and quality are important factors in the determination of bone strength. Collagen crosslinking is a determinant of bone quality. Cross-links can form enzymatically by the action of lysyl oxidase or non-enzymatically, resulting in advanced glycation end products. Collagen crosslinking is affected by tissue maturation as well as the degree of mineralization. Homocysteine and vitamin B6 (pyridoxal) are also regulatory factors of collagen crosslinking. We elucidate the relationship between the degree of mineralization and collagen cross-links in cancellous bone from hip fracture cases. We also determined plasma levels of homocysteine and pyridoxal. Twenty-five female intracapsular hip fracture cases (78 +/- 6 years) and 25 age-matched postmortem controls (77 +/- 6 years) were included in this study. Collagen crosslinking was analyzed after each bone specimen was fractionated into low (1.7-2.0 g/ml) and high (>2.0 g/ml) density fractions. The content of enzymatic (immature reducible and mature nonreducible cross-links) and nonenzymatic cross-link (pentosidine) were determined. In the controls, there was no difference in total enzymatic cross-links between low and high density bone, while pentosidine content was significantly higher in high density bone. In the fracture cases, not only reduced enzymatic cross-links in high density bone and increased pentosidine in both low and high density bone, but also higher plasma homocysteine and lower pyridoxal levels were evident compared with the controls. These results indicate that detrimental crosslinking in both low and high mineralized bone result in impaired bone quality in osteoporotic patients.

Reductions in degree of mineralization and enzymatic collagen cross-links and increases in glycation-induced pentosidine in the femoral neck cortex in cases of femoral neck fracture

INTRODUCTION

Enzymatic and glycation-induced nonenzymatic cross-links play important roles in the expression of bone strength. The cross-link pattern is affected by tissue maturation and senescence. The aim of our study was to understand the distinctive posttranslational modifications of collagen in areas with different degrees of mineralization with and without hip fracture.

METHODS

Sixteen female cases of intracapsular hip fracture (78+/-6 years) and 16 age- and gender-matched postmortem controls (76+/-6 years) were included in this study. A sample of each femoral neck cortex was fractionated into low (1.7 to 2.0 g/ml) and high (>2.0 g/ml) density portions. The contents of enzymatic cross-links (dihydroxylysinonorleucine, hydroxylysinonorleucine, lysinonorleucine, pyridinoline, and deoxypyridinoline) and nonenzymatic cross-links (pentosidine) and the extent of lysine (Lys) hydroxylation were determined in each fraction.

RESULTS

In the controls, there was no significant difference in the contents of enzymatic cross-links between low- and high-mineralized bone fractions whereas pentosidine content was significantly higher in high-mineralized bone compared with low-mineralized bone (p=0.0014). When comparing enzymatic cross-link contents between controls and fracture cases, a trend toward lower (p=0.0961) cross-link content in low-mineralized bone and a significant reduction (p<0.0001) in high-mineralized bone were observed. Pentosidine content of low-mineralized bone was significantly higher in fracture cases than in controls (p<0.0001). The extent of Lys hydroxylation was significantly higher in fracture cases than in controls (p<0.001). The higher hydroxylation of Lys in collagen from fracture cases relative to controls was associated with significantly higher values of hydroxylysine-derived cross-link such that the enzymatic cross-link patterns correlated with the extent of Lys hydroxylation in the collagen molecules.

CONCLUSIONS

These results suggest that reductions in the degree of mineralization and enzymatic cross-links and excessive formation of pentosidine may play an important role in explaining poor bone quality in osteoporosis.