Calcified Matrix Research Articles

Uncoupling the Vicious Cycle of Mechanical Stress and Inflammation in Calcific Aortic Valve Disease.

Calcific aortic valve disease (CAVD) is a common acquired valvulopathy, which carries a high burden of mortality. Chronic inflammation has been postulated as the predominant pathophysiological process underlying CAVD. So far, no effective medical therapies exist to halt the progression of CAVD. This review aims to outline the known pathways of inflammation and calcification in CAVD, focussing on the critical roles of mechanical stress and mechanosensing in the perpetuation of valvular inflammation. Following initiation of valvular inflammation, dysregulation of proinflammatory and osteoregulatory signalling pathways stimulates endothelial-mesenchymal transition of valvular endothelial cells (VECs) and differentiation of valvular interstitial cells (VICs) into active myofibroblastic and osteoblastic phenotypes, which in turn mediate valvular extracellular matrix remodelling and calcification. Mechanosensitive signalling pathways convert mechanical forces experienced by valve leaflets and circulating cells into biochemical signals and may provide the positive feedback loop that promotes acceleration of disease progression in the advanced stages of CAVD. Mechanosensing is implicated in multiple aspects of CAVD pathophysiology. The mechanosensitive RhoA/ROCK and YAP/TAZ systems are implicated in aortic valve leaflet mineralisation in response to increased substrate stiffness. Exposure of aortic valve leaflets, endothelial cells and platelets to high shear stress results in increased expression of mediators of VIC differentiation. Upregulation of the Piezo1 mechanoreceptor has been demonstrated to promote inflammation in CAVD, which normalises following transcatheter valve replacement. Genetic variants and inhibition of Notch signalling accentuate VIC responses to altered mechanical stresses. The study of mechanosensing pathways has revealed promising insights into the mechanisms that perpetuate inflammation and calcification in CAVD. Mechanotransduction of altered mechanical stresses may provide the sought-after coupling link that drives a vicious cycle of chronic inflammation in CAVD. Mechanosensing pathways may yield promising targets for therapeutic interventions and prognostic biomarkers with the potential to improve the management of CAVD.

Protective Roles of Xenotropic and Polytropic Retrovirus Receptor 1 (XPR1) in Uremic Vascular Calcification.

Cellular phosphate transporters play critical roles in the pathogenesis of vascular calcification (VC) in chronic kidney disease (CKD). However, the mechanistic link between VC and xenotropic and polytropic receptor 1 (XPR1), a newly identified phosphate exporter, remains unknown. We developed a new mouse model with rapidly progressive uremic VC in C57BL/6 mice and examined the roles of XPR1. The combination of surgical heminephrectomy and 8weeks of feeding a customized warfarin and adenine-based diet induced extensive aortic VC in almost all mice. The XPR1 mRNA level in the aorta of CKD mice was significantly lower than those in control mice as early as week 2, when there was no apparent VC, which progressively declined thereafter. Dietary phosphate restriction increased XPR1 mRNA expression in the aorta but reduced aortic VC in CKD mice. In cultured vascular smooth muscle cells (VSMCs), a calcifying medium supplemented with high phosphate and calcium did not affect XPR1 mRNA expression. The XPR1 mRNA expression in cultured VCMCs was also unaffected by administration of indoxyl sulfate or calcitriol deficiency but was decreased by 1-34 parathyroid hormone or fibroblast growth factor 23 supplementation. Furthermore, XPR1 deletion in the cultured VSMCs exacerbated calcification of the extracellular matrix as well as the osteogenic phenotypic switch under the condition of calcifying medium. Our data suggest that XPR1 plays protective roles in the pathogenesis of VC and its decrease in the aorta may contribute to the progression of VC in CKD.

Extracellular DNA: A Missing Link in the Pathogenesis of Ectopic Mineralization (Adv. Sci. 5/2022)

Extracellular DNA In article number 2103693, Li-na Niu and co-workers discuss a fascinating novel function of extracellular DNA as mineralization initiators in ectopic calcification. Extracellular DNAs regulate matrix calcification outside cells and participate in extracellular mineral nucleation and collagen mineralization. This significant discovery enables facile preparation of biomimetic hybrid materials for tissue engineering and provides a potential solution for treatment of diseases associated with ectopic mineralization.

Grade 1 and 2 Chondrosarcomas of the Chest Wall: CT Imaging Features and Review of the Literature.

The purpose of our retrospective article is to review the CT imaging features of chondrosarcomas of the chest wall with pathologic correlation. For 26 subjects with biopsy-proven chondrosarcomas of the chest wall, two musculoskeletal radiologists retrospectively reviewed 26 CT scans in consensus. Descriptive statistics were performed. The mean tumor size was 57 mm. Twenty (20/26, 77%) chondrosarcomas were located in the ribs and six (6/26, 23%) in the sternum. The majority were lytic (19/26, 73%) with <25% calcification (15/26, 58%), and with a soft tissue mass (22/27, 85%). In this study CT features of grade 1 chondrosarcoma overlapped with those of grade 2 tumors. In conclusion, chondrosarcomas of the chest wall are generally lytic with an associated soft tissue mass, showing little calcified matrix and low-to-intermediate grade.

Calcified aortic valve disease complicated with and without diabetes mellitus: the underlying pathogenesis.

As the most prevalent valvular heart disease, calcific aortic valve disease (CAVD) is a major health problem with risk of severe morbidity and mortality in the absence of effective medical treatment beyond surgical or interventional aortic valve replacement. The pathology involved in CAVD is multifactorial, including valvular endothelial cells damage, valvular interstitial cells differentiation, extracellular matrix remodeling, inflammation, fibrosis and calcification. Various risk factors for CAVD have been reported, such as age, gender, smoking, hyperlipidemia, hypertension, obesity and bicuspid aortic valves. Recently, diabetes mellitus has also been shown to accelerate the progression of CAVD. CAVD patients complicated with diabetes mellitus may benefit from early aortic valve replacement when compared with those without diabetes mellitus. Hence, diabetes mellitus is considered as an independent risk factor for CAVD. Therefore, in-depth understanding of the pathogenesis of these two diseases and their relationship may help us find appropriate prevention and therapeutic strategies for CAVD patients complicated with diabetes mellitus.

Strategies for accelerating osteogenesis through nanoparticle-based DNA/mitochondrial damage repair.

The efficiency of gene therapy is often dictated by the gene delivery system. Cationic polymers are essential elements of gene delivery systems. The relatively cheap cationic polymer, polyethyleneimine, has high gene delivery efficiency and is often used for gene delivery. However, the efficiency of gene therapy with polyethyleneimine-pDNA polyplex (PEI) is low. Human mesenchymal stem cells transfected with polyethyleneimine and a plasmid carrying the important osteogenic differentiation gene runt-related transcription factor 2 (RUNX2) accumulated DNA double-strand breaks and mitochondrial damage proportional to the amount of polyethyleneimine, reducing viability. Genomic/cellular stabilizer mediating RUNX2 delivery (GuaRD), a new reagent incorporating RS-1 NPs developed in this study, promoted DNA repair and prevented the accumulation of cell damage, allowing the delivery of pRUNX2 into hMSCs. while maintaining genome and mitochondrial stability. DNA damage was significantly lower and the expression of DNA repair-related genes significantly higher with GuaRD than with PEI. In addition, GuaRD improved mitochondrial stability, decreased the level of reactive oxygen species, and increased mitochondrial membrane potential. Osteogenic extracellular matrix (ECM) expression and calcification were higher with GuaRD than with PEI, suggesting improved osteogenic differentiation. These results indicate that lowering the cytotoxicity of PEI and improving cell stability are key to overcoming the limitations of conventional gene therapy, and that GuaRD can help resolve these limitations.

Preparation and characterization of Mg(II) doped hydroxyapatite biocomposites

Bone tissue is a calcified matrix formed mainly by hydroxyapatite (HAp). Given the chemical similarity of HAp with several phosphate salts, researchers have been using them to develop clinical scaffolds for bone repair applications. Calcium polyphosphate (CPP) is an inorganic matrix, which presents biocompatibility and low toxicity, however it is brittle, requiring their association with polymers, such as alginate, to improve their mechanical properties. Furthermore, Mg2+ ions are present in the biological medium, participating in acid-base processes that modulate bone calcification and decalcification. Thus, incorporating Mg2+ ions and alginate in HAp could improve its bioactivity. In this context, this work presents the development of composite materials based on calcium polyphosphate, alginate, and magnesium, as candidates for bone tissue applications, using a simple and practical method, with low temperature. The preparation of the composites was achieved by precipitation of CPP in an aqueous medium containing the pre-solubilized alginate, followed by the addition of Mg2+. The materials were characterized by Raman and infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and dispersive energy spectroscopy. The results confirmed the formation of the desired composites with the hydroxyapatite structure, and with the potential to be evaluated for bone repair applications.

DIFFERENTIATION POTENTIAL OF THE MESENCHYMAL STROMAL CELLS DURING REPLICATIVE SENESCENCE

Mesenchymal stromal/stem cells (MSCs) are capable of multilinear differentiation and participate in tissue homeostasis including the remodeling and reparation processes. With aging these cells more and more often activatesenescence (cell aging) that alters cell functions and microenvironment which can be the reason for age-related pathologies. One of the features of senescent MSCs is thought to be a decline of multipotency that may limit their reparative functions in tissues. The paper presents a study of the MSCs osteogenic and adipogenic potential during replicative senescence. A decline of the MSCs adipogenic potential was associated with downregulation of PPARG,(a key transcription regulator of adipogenesis). There was evidence of reciprocal increasing of the osteogenic potential even though the several positive osteogenesis regulators (BMP2, BMP6, IGF1, IL1B) were downregulated. Besides, during differentiation matrix calcification was enhanced and osteoprotegerin concentration increased that can be an issue in context of atherosclerotic plaques calcification in elder people. Expression of key osteogenesis regulator RUNX2 and markers SPARC, SPP1, COL1A1, BGLAP remained stable during replicative senescence of MSCs.

Correlation between radiographic and histopathological findings of conventional osteosarcoma subtypes: osteoblastic, chondroblastic, and fibroblastic

Background: Osteosarcoma is a connective tissue malignancy producing osteoid and some cartilaginous and fibrous matrix. It provides a challenging diagnostic approach since it is considered as a great mimicker in radiography and histopathology appearance. Triple diagnostic approach is mandatory, involving the clinical, radiologic and histopathologic aspect of all cases suspected. This study aimed to discover the correlation between radiographic and histopathological findings of fibroblastic, chondroblastic and osteoblastic subtypes of conventional osteosarcoma. Methods: This study implemented a cross-sectional study design. Components of radiographic findings of conventional osteosarcoma were bone destruction, transitional zone, periosteal reaction, matrix of calcification, skip lesion and soft tissue mass which were analyzed and correlated with its histopathological subtype. Statistical analysis was performed using the Spearman correlation test with p-value &lt; 0.05.Results: Significant negative correlation was obtained between chondroid matrix calcification and histopathology description of conventional osteosarcoma with osteoblastic subtype (r = -0.383; p &lt; 0.05) and negative correlation between osteoid matrix and histopathologic analysis of fibroblastic subtype (r = -0.435; p &lt; 0.05). All of the radiographic components of the chondroblastic subtype did not show significant correlation with their histopathological findings.Conclusion: Chondroid matrix finding in radiography showed negative correlation with histopathologic evaluation of osteoblastic subtype while osteoid matrix description in radiography had negative correlation with histopathologic analysis of fibroblastic subtype.

Enhanced carbonic anhydrase expression with calcification and fibrosis in bronchial cartilage during COPD

Pulmonary cartilage plays a crucial structural role determining the physiologic airway compressibility and distensibility, necessary for proper mechanical function. This functionality deteriorates with aging due to increased stiffness of both airway muscle and cartilage, as well as, decreased renewal capacity. Altered airway remodeling has been suggested as a pathogenic driver of chronic obstructive pulmonary disease (COPD) through mechanisms still incompletely understood. Using paraffin-embedded lung tissue sections from archived autopsy material from COPD with non-COPD age matched controls a histopathologic analysis focused on inflammation, fibrosis and calcification was performed with special stains (Masson’s trichrome and Von Kossa) and immunohistochemistry for carbonic anhydrase IV (CA IV) and Ki-67. COPD lung tissues showed increased peribronchial inflammation compared to the non-COPD. Coarse amphophilic crystalline deposits in bronchial cartilage were more frequently observed in COPD sections, which were compatible with early dystrophic calcification of the extracellular matrix and chondrocytes. Moreover, Von Kossa staining revealed a significant calcium deposition in the cartilages from COPD in comparison to the controls. Interestingly, Ki-67 immunostains demonstrated a higher overall proliferative rate, including epithelial cells, in COPD. Furthermore, Masson’s trichrome staining revealed relatively increased peribronchial collagen deposition associated with a fibrotic stromal response, which may be secondary to the inflammatory milieu in COPD. To further characterize the tissue microenvironment associated with dystrophic calcification, immunohistochemistry for CA IV was used, revealing significantly increased expression in chondrocytes and peribronchial tissue in COPD. Our findings demonstrate that dystrophic calcification of the extracellular matrix and chondrocytes can be linked to CA IV expression in COPD and suggest that pH changes in pulmonary tissue associated with inflammation and calcification may play an active role in COPD.

Imaging features of cartilaginous tumors of the head and neck.

There is a wide spectrum of head and neck cartilaginous lesions which include both neoplastic and nonneoplastic processes. Cartilaginous tumors of the head and neck are uncommon, posing a diagnostic challenge. Benign cartilaginous tumors that may occur in the head and neck include chondroma, chondroblastoma, chondromyxoid fibroma, osteochondroma, and synovial chondromatosis. Chondromesenchymal hamartoma is a rare non-neoplastic cartilaginous lesion that is included for the 1first time in the new WHO classification and radiologically can mimic a tumor. Malignant cartilaginous tumors include chondrosarcoma and chondroid variant of chordoma. Characteristic tumor locations, internal chondroid matrix calcification, and typical T2 hyperintense signal secondary to high-water content within the extracellular matrix of the hyaline cartilage are useful imaging features that narrow the differential diagnosis and help in diagnosing these diseases. This article presents a narrative review of the anatomy of the head and neck cartilaginous structures, discusses the current knowledge and imaging spectrum of benign and malignant cartilaginous tumors and tumor-like lesions of the head and neck.

Calcification and resorption of mouse Meckel's cartilage analyzed by von Kossa and tartrate-resistant acid phosphatase histochemistry and scanning electron microscopy/energy-dispersive X-ray spectrometry.

Meckel's cartilage is essential for the normal development of the mandible. The fate of the intermediate portion of Meckel's cartilage is unique as most of it disappears soon after birth except for the part that forms the sphenomandibular ligament. The mechanism of the disappearance of Meckel's cartilage is unknown; therefore, this study was designed to investigate the process of Meckel's cartilage degradation, focusing on cartilage matrix calcification and the appearance of chondroclasts. Developing mouse mandibles at embryonic days 15, 16, 17, and 18, and postnatal day 2 were processed for whole-mount staining with alcian blue and alizarin red. The mandibles on embryonic days 15, 16, 17, and 18 were fixed and embedded in paraffin. Adjacent sections were processed for von Kossa and tartrate-resistant acid phosphatase (TRAP) histochemistry and scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS). Calcification and the element concentrations of calcium, phosphorus, and carbon were examined with von Kossa histochemistry and SEM/EDS. The involvement of chondroclasts was investigated using TRAP histochemistry. The results demonstrated that the intermediate portion of Meckel's cartilage is resorbed by chondroclasts after chondrocyte hypertrophy and cartilage matrix calcification and that the mineral concentration of calcified Meckel's cartilage is comparable to that of the surrounding bone. This study contributes to the understanding of the mechanism of Meckel's cartilage resorption and provides useful insights into the development of the mandible.

Multicentric epithelioid hemangioendothelioma of humerus and scapula

Epithelioid hemangioendothelioma (EH) is a rare malignant vascular tumor occurring mainly in the liver and lungs, with bones being a rare site and primarily seen in the adult population. We present a rare case of multicentric EH in the right humerus in an adolescent male, who presented with complaints of pain and swelling in the right shoulder. Radiographs and Computed tomography showed a large expansile lytic lesion in the proximal end of the right humerus with areas of cortical destruction and matrix calcification. On Magnetic resonance imaging, the lesion was predominantly isointense on T1-weighted image, hyperintense on T2-weighted, and Short Tau Inversion Recovery images with prominent flow voids within. On post-contrast sequences, the lesion showed intense heterogenous enhancement with a non-enhancing central necrotic area. Multiple smaller lytic lesions with similar imaging characteristics were also found in the mid and distal shaft of the right humerus and the right coracoid process. Differentials of Telangiectatic osteosarcoma, Giant cell tumor, brown tumors of hyperparathyroidism, and metastasis were considered. Core biopsy revealed that the lesion was an EH. Though the imaging features of EH are non-specific, it may be considered in the differential diagnosis of an expansile lytic bone lesion with no periosteal reaction, showing cortical break and soft tissue component, especially if it is multifocal and multicentric.

Progenitor Cells in Healthy and Osteoarthritic Human Cartilage Have Extensive Culture Expansion Capacity while Retaining Chondrogenic Properties.

Articular cartilage-derived progenitor cells (ACPCs) are a potential new cell source for cartilage repair. This study aims to characterize endogenous ACPCs from healthy and osteoarthritic (OA) cartilage, evaluate their potential for cartilage regeneration, and compare this to cartilage formation by chondrocytes. ACPCs were isolated from full-thickness healthy and OA human cartilage and separated from the total cell population by clonal growth after differential adhesion to fibronectin. ACPCs were characterized by growth kinetics, multilineage differentiation, and surface marker expression. Chondrogenic redifferentiation of ACPCs was compared with chondrocytes in pellet cultures. Pellets were assessed for cartilage-like matrix production by (immuno)histochemistry, quantitative analyses for glycosaminoglycans and DNA content, and expression of chondrogenic and hypertrophic genes. Healthy and OA ACPCs were successfully differentiated toward the adipogenic and chondrogenic lineage, but failed to produce calcified matrix when exposed to osteogenic induction media. Both ACPC populations met the criteria for cell surface marker expression of mesenchymal stromal cells (MSCs). Healthy ACPCs cultured in pellets deposited extracellular matrix containing proteoglycans and type II collagen, devoid of type I collagen. Gene expression of hypertrophic marker type X collagen was lower in healthy ACPC pellets compared with OA pellets. This study provides further insight into the ACPC population in healthy and OA human articular cartilage. ACPCs show similarities to MSCs, yet do not produce calcified matrix under well-established osteogenic culture conditions. Due to extensive proliferative potential and chondrogenic capacity, ACPCs show potential for cartilage regeneration and possibly for clinical application, as a promising alternative to MSCs or chondrocytes.

Low kindlin-3 levels in osteoclasts of kindlin-3 hypomorphic mice result in osteopetrosis due to leaky sealing zones.

Osteoclasts form special integrin-mediated adhesion structures called sealing zones that enable them to adhere to and resorb bone. Sealing zones consist of densely packed podosomes tightly interconnected by actin fibers. Their formation requires the presence of the hematopoietic integrin regulator kindlin-3 (also known as Fermt3). In this study, we investigated osteoclasts and their adhesion structures in kindlin-3 hypomorphic mice expressing only 5-10% of the kindlin-3 level of wild-type mice. Low kindlin-3 expression reduces integrin activity, results in impaired osteoclast adhesion and signaling, and delays cell spreading. Despite these defects, in vitro-generated kindlin-3-hypomorphic osteoclast-like cells arrange their podosomes into adhesion patches and belts, but their podosome and actin organization is abnormal. Remarkably, kindlin-3-hypomorphic osteoclasts form sealing zones when cultured on calcified matrix in vitro and on bone surface in vivo. However, functional assays, immunohistochemical staining and electron micrographs of bone sections showed that they fail to seal the resorption lacunae properly, which is required for secreted proteinases to digest bone matrix. This results in mild osteopetrosis. Our study reveals a new, hitherto understudied function of kindlin-3 as an essential organizer of integrin-mediated adhesion structures, such as sealing zones.

Bone Regeneration Using MMP-Cleavable Peptides-Based Hydrogels.

Accumulating evidence has suggested the significant potential of chemically modified hydrogels in bone regeneration. Despite the progress of bioactive hydrogels with different materials, structures and loading cargoes, the desires from clinical applications have not been fully validated. Multiple biological behaviors are orchestrated precisely during the bone regeneration process, including bone marrow mesenchymal stem cells (BMSCs) recruitment, osteogenic differentiation, matrix calcification and well-organized remodeling. Since matrix metalloproteinases play critical roles in such bone metabolism processes as BMSC commitment, osteoblast survival, osteoclast activation matrix calcification and microstructure remodeling, matrix metalloproteinase (MMP) cleavable peptides-based hydrogels could respond to various MMP levels and, thus, accelerate bone regeneration. In this review, we focused on the MMP-cleavable peptides, polymers, functional modification and crosslinked reactions. Applications, perspectives and limitations of MMP-cleavable peptides-based hydrogels for bone regeneration were then discussed.

Role of Runx2 in Calcific Aortic Valve Disease in Mouse Models.

Background: Calcific aortic valve disease is common in the aging population and is characterized by the histological changes of the aortic valves including extracellular matrix remodeling, osteochondrogenic differentiation, and calcification. Combined, these changes lead to aortic sclerosis, aortic stenosis (AS), and eventually to heart failure. Runt-related transcription factor 2 (Runx2) is a transcription factor highly expressed in the calcified aortic valves. However, its definitive role in the progression of calcific aortic valve disease (CAVD) has not been determined. In this study, we utilized constitutive and transient conditional knockout mouse models to assess the molecular, histological, and functional changes in the aortic valve due to Runx2 depletion.Methods: Lineage tracing studies were performed to determine the provenance of the cells giving rise to Runx2+ osteochondrogenic cells in the aortic valves of LDLr−/− mice. Hyperlipidemic mice with a constitutive or temporal depletion of Runx2 in the activated valvular interstitial cells (aVICs) and sinus wall cells were further investigated. Following feeding with a diabetogenic diet, the mice were examined for changes in gene expression, blood flow dynamics, calcification, and histology.Results: The aVICs and sinus wall cells gave rise to Runx2+ osteochondrogenic cells in diseased mouse aortic valves. The conditional depletion of Runx2 in the SM22α+ aVICs and sinus wall cells led to the decreased osteochondrogenic gene expression in diabetic LDLr−/− mice. The transient conditional depletion of Runx2 in the aVICs and sinus wall cells of LDLr−/−ApoB100 CAVD mice early in disease led to a significant reduction in the aortic peak velocity, mean velocity, and mean gradient, suggesting the causal role of Runx2 on the progression of AS. Finally, the leaflet hinge and sinus wall calcification were significantly decreased in the aortic valve following the conditional and temporal Runx2 depletion, but no significant effect on the valve cusp calcification or thickness was observed.Conclusions: In the aortic valve disease, Runx2 was expressed early and was required for the osteochondrogenic differentiation of the aVICs and sinus wall cells. The transient depletion of Runx2 in the aVICs and sinus wall cells in a mouse model of CAVD with a high prevalence of hemodynamic valve dysfunction led to an improved aortic valve function. Our studies also suggest that leaflet hinge and sinus wall calcification, even in the absence of significant leaflet cusp calcification, may be sufficient to cause significant valve dysfunctions in mice.

Biomimicking Bone-Implant Interface Facilitates the Bioadaption of a New Degradable Magnesium Alloy to the Bone Tissue Microenvironment.

The most critical factor determining the success of biodegradable bone implants is the host tissue response, which greatly depends on their degradation behaviors. Here, a new magnesium‐based implant, namely magnesium–silicon–calcium (Mg–0.2Si–1.0Ca) alloy, that coordinates its biodegradation along with the bone regenerative process via a self‐assembled, multilayered bone–implant interface is designed. At first, its rapid biocorrosion contributes to a burst release of Mg2+, leading to a pro‐osteogenic immune microenvironment in bone. Meanwhile, with the simultaneous intervention of Ca and Si in the secondary phases of the new alloy, a hierarchical layered calcified matrix is rapidly formed at the degrading interface that favored the subsequent bone mineralization. In contrast, pure Mg or Mg–0.2Si alloy without the development of this interface at the beginning will unavoidably induce detrimental bone loss. Hence, it is believed this biomimicking interface justifies its bioadaptability in which it can modulate its degradation in vivo and accelerate bone mineralization.

A Three-Dimensional Mechanical Loading Model of Human Osteocytes in Their Native Matrix

Osteocytes are mechanosensory cells which are embedded in calcified collagenous matrix. The specific native matrix of osteocytes affects their regulatory activity, i.e., transmission of signaling molecules to osteoclasts and/or osteoblasts, in the mechanical adaptation of bone. Unfortunately, no existing in vitro model of cortical bone is currently available to study the mechanosensory function of human osteocytes in their native matrix. Therefore, we aimed to develop an in vitro three-dimensional mechanical loading model of human osteocytes in their native matrix. Human cortical bone explants containing osteocytes in their three-dimensional native matrix were cultured and mechanically loaded by three-point bending using a custom-made loading apparatus generating sinusoidal displacement. Osteocyte viability and sclerostin expression were measured 1–2 days before 5 min loading and 1 day after loading. Bone microdamage was visualized and quantified by micro-CT analysis and histology using BaSO4 staining. A linear relationship was found between loading magnitude (2302–13,811 µɛ) and force (1.6–4.9 N) exerted on the bone explants. At 24 h post-loading, osteocyte viability was not affected by 1600 µɛ loading. Sclerostin expression and bone microdamage were unaffected by loading up to 8000 µɛ. In conclusion, we developed an in vitro 3D mechanical loading model to study mechanoresponsiveness of viable osteocytes residing in their native matrix. This model is suitable to study the effect of changed bone matrix composition in metabolic bone disease on osteocyte mechanoresponsiveness.

Rivaroxaban attenuates valvular inflammation and tissue remodeling in patients with severe aortic stenosis

Abstract Background It has been demonstrated in a mouse model of atherosclerosis that non-vitamin K antagonist oral anticoagulants (NOACs) attenuate atherosclerotic plaque progression. However, it is not known whether NOACs can inhibit aortic stenosis (AS) progression. Aims To evaluate whether rivaroxaban at therapeutic concentrations can impair valvular inflammation and valve remodeling in patients with severe AS. Methods We recruited 38 patients with isolated severe AS aged 68±8 years (mean gradient 54 mmHg, max gradient 86 mmHg), including 18 individuals with AS and atrial fibrillation taking rivaroxaban (20 mg/daily for at least 3 years). Stenotic aortic valves were obtained during valve replacement surgery. Valvular expression of NFκB, matrix metalloproteinase 9 (MMP-9) and bone morphogenetic protein 2 (BMP-2) was evaluated by immunostaining. Primary cultures of valve interstitial cells (VICs) obtained from stenotic aortic valves were stimulated with TNF-α to induce inflammation. In parallel, VICs were cultured with TNF-α and rivaroxaban at therapeutic concentrations (1 and 10 μg/ml, corresponding to about 2.5 mg and 25 mg daily in vivo). The expression of NFκB, interleukin 1β (IL-1β), reactive oxygen species (ROS), MMP-9 and BMP-2 in VICs was assessed. The control VICs were cultured without any additives. All VICs were cultured for 72 hours and experiments were repeated 3 times. The fluorescence intensity was computed as the ratio (%) of positively and negatively stained areas. Results We observed decreased valvular expression of NFκB (−54%), MMP-9 (−32%) and BMP-2 (−23%) in patients taking rivaroxaban compared to those without such treatment. TNF-α stimulation up-regulated expression of NFκB, IL-1β and ROS (+58%; +34%; +38%; all p&amp;lt;0.01) accompanied by higher expression of MMP-9 and BMP-2 (+49% for MMP-9 and +32% for BMP-2; both p&amp;lt;0.01), when compared to control cells. Rivaroxaban at a concentration of 10 μg/ml decreased the expression of ROS (−31%, p&amp;lt;0.01), inflammatory markers (NFκB −47% and IL-1β −22%, both p&amp;lt;0.01) and MMP-9 (−39%, p&amp;lt;0.01) compared to VICs cultured without rivaroxaban. Similarly, BMP-2 expression was down regulated after 10 μg/ml of rivaroxaban (−26%, p&amp;lt;0.01). Even low dose of rivaroxaban decreased VICs expression of NFκB, IL-1β and ROS by 38%, 18% and 25%, respectively (all p&amp;lt;0.01) as compared to cells stimulated with TNF-α only. Comparable effect was observed for MMP-9 and BMP-2 expression (−33%; −22%; both p&amp;lt;0.01). Conclusions Rivaroxaban can decrease valvular inflammation and its remodelling and significantly inhibits inflammation, extracellular matrix activity and calcification of VICs. Our study suggests that NOACs, even at a low dose, could slow the rate of AS progression, at least in AS patients with mild-to-moderate AS and indications for anticoagulant therapy. Clinical relevance of these findings requires further studies. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Science Centre (NCN)