Contribution of calcium-containing crystals to cartilage degradation and synovial inflammation in osteoarthritis

Discovery of calcite as a new pro-inflammatory calcium-containing crystal in human osteoarthritic synovial fluid

OBJECTIVE

We aimed to characterize calcium-containing crystals present in synovial fluid from patients with knee osteoarthritis (OA) using Raman spectroscopy, and specifically investigate the biological effects of calcite crystals.

DESIGN

Thirty-two synovial fluid samples were collected pre-operatively from knee OA patients undergoing total joint arthroplasty. An integrated Raman polarized light microscope was used for identification of crystals in synovial fluid. Human peripheral blood mononuclear cells (PBMC's), human OA articular chondrocytes (HACs) and fibroblast-like synoviocytes (FLSs) were exposed to calcite crystals. Expression of relevant cytokines and inflammatory genes were measured using ELISA and real-time PCR.

RESULTS

Various calcium-containing crystals were identified, including calcium pyrophosphate (37.5 %) and basic calcium phosphate (21.8 %), but they were never found simultaneously in the same OA synovial fluid sample. For the first time, we discovered the presence of calcite crystals in 93.8 % of the samples, while dolomite was detected in 25 % of the cases. Characterization of the cellular response to calcite crystal exposure revealed increased production of innate immune-derived cytokines by PBMC's, when co-stimulated with lipopolysaccharide (LPS). Additionally, calcite crystal stimulation of HACs and FLSs resulted in enhanced secretion of pro-inflammatory molecules and alterations in the expression of extracellular matrix remodeling enzymes.

CONCLUSIONS

This study highlights the unique role of Raman spectroscopy in OA crystal research and identified calcite as a novel pro-inflammatory crystal type in OA synovial fluid. Understanding the role of specific crystal species in the OA joint may open new avenues for pharmacological interventions and personalized approaches to treating OA.

Cartilage calcification in osteoarthritis: mechanisms and clinical relevance

Pathological calcification of cartilage is a hallmark of osteoarthritis (OA). Calcification can be observed both at the cartilage surface and in its deeper layers. The formation of calcium-containing crystals, typically basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate (CPP) crystals, is an active, highly regulated and complex biological process that is initiated by chondrocytes and modified by genetic factors, dysregulated mitophagy or apoptosis, inflammation and the activation of specific cellular-signalling pathways. The links between OA and BCP deposition are stronger than those observed between OA and CPP deposition. Here, we review the molecular processes involved in cartilage calcification in OA and summarize the effects of calcium crystals on chondrocytes, synovial fibroblasts, macrophages and bone cells. Finally, we highlight therapeutic pathways leading to decreased joint calcification and potential new drugs that could treat not only OA but also other diseases associated with pathological calcification.

Crowned Dens Syndrome: A Rare Complication of Calcium Pyrophosphate Crystal Deposition Disease

Crowned dens syndrome (CDS) is a clinical entity characterized by neck pain associated with fever, headaches, and neck stiffness, along with radiologic evidence of peri-odontoid process calcification in a characteristic “crown” or “halo” distribution. It is likely an underdiagnosed condition and patients can initially be misdiagnosed, leading to costly evaluation and unnecessary treatment interventions. We present the case of a 76-year-old man who presented to the emergency department (ED) with a 3-day history of progressively worsening neck pain that was associated with headaches, malaise, decreased oral intake, chills, and fever. Initial evaluation was significant for the presence of fever, tachycardia, and elevated inflammatory markers. We report a case of CDS attributed to calcium pyrophosphate deposition and review the pertinent literature about the presentation, diagnostic evaluation, and treatment of this rare clinical entity.

Chondrocyte-derived exosomes promote cartilage calcification in temporomandibular joint osteoarthritis

BACKGROUNDS

Abnormal cartilage calcification is one of the pathological changes of temporomandibular joint (TMJ) osteoarthritis (OA). Recent studies have reported that exosomes can regulate the formation of abnormal calcified nodules in diseases including atherosclerosis and chronic kidney disease. However, the influences of chondrocyte-derived exosomes on abnormal cartilage calcification in TMJ OA are still unclear.

METHODS

TMJ OA was induced by unilateral anterior crossbite (UAC) for 4, 8, or 12 weeks in rats to observe abnormal calcification in TMJ condylar cartilage and exosome formation. Concomitantly, GW4869, the inhibitor of exosome formation, was locally injected to the TMJ of rats under stimulation of UAC, while the exosomes extracted from primary condylar chondrocytes stimulated with fluid flow shear stress (FFSS) were locally injected to rats TMJ.

RESULTS

Abnormal calcification was enhanced in the degenerative cartilage of TMJ OA in UAC rats, and a large number of exosome-like structures with diameters of 50-150 nm were found in the calcified cartilage together with decreased expression of matrix Gla protein (MGP) and increased expression of CD63, tissue-nonspecific alkaline phosphatase (TNAP) and nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1). After FFSS stimulation, the number of exosomes secreted by chondrocytes and the numbers of calcified nodules were increased in cultured cells, and the protein levels of MGP, TNAP, and NPP1 in exosomes were changed. Inhibition of exosome formation, TNAP, and NPP1 or supplementation with exogenous MGP effectively alleviated FFSS-induced chondrocyte calcification. Local injection of GW4869, the exosome inhibitor, alleviated TMJ OA-related cartilage degeneration and calcification in UAC rats. Local injection of exosomes obtained from chondrocytes stimulated by FFSS to the TMJs of normal rats induced cartilage degeneration and calcification similar to that in TMJ OA.

CONCLUSIONS

Abnormal biomechanical loading leads to enhanced formation of chondrocyte-derived exosomes, in which promoters of calcification increased and inhibitors decreased, resulting in accelerating abnormal cartilage calcification in TMJ OA. The inhibition of degenerative chondrocyte-derived exosomes is expected to be a new way to prevent and treat TMJ OA.

Amorphous-mediated crystallization of calcium pyrophosphate tetrahydrate: the role of alkaline earth metal ions

Although calcium pyrophosphates are commonly involved in crystal arthropathies, their formation mechanisms remain largely underexplored. Here, we investigated the crystallization pathway of calcium pyrophosphate tetrahydrate in the absence and presence...

Injectable hydrogel mediated delivery of gene-engineered adipose-derived stem cells for enhanced osteoarthritis treatment

Osteoarthritis (OA), a chronic and degenerative joint disease, remains a challenge in treatment due to the lack of disease-modifying therapies. As a promising therapeutic agent, adipose-derived stem cells (ADSCs) have an effective anti-inflammatory and chondroprotective paracrine effect that can be enhanced by genetic modification. Unfortunately, direct cell delivery without matrix support often results in poor viability of therapeutic cells. Herein, a hydrogel implant approach that enabled intra-articular delivery of gene-engineered ADSCs was developed for improved therapeutic outcomes in a surgically induced rat OA model. An injectable extracellular matrix (ECM)-mimicking hydrogel was prepared as the carrier for cell delivery, providing a favorable microenvironment for ADSC spreading and proliferation. The ECM-mimicking hydrogel could reduce cell death during and post injection. Additionally, ADSCs were genetically modified to overexpress transforming growth factor-β1 (TGF-β1), one of the paracrine factors that exert an anti-inflammatory and pro-anabolic effect. The gene-engineered ADSCs overexpressing TGF-β1 (T-ADSCs) had an enhanced paracrine effect on OA-like chondrocytes, which effectively decreased the expression of tumor necrosis factor-alpha and increased the expression of collagen II and aggrecan. In a surgically induced rat OA model, intra-articular injection of the T-ADSC-loaded hydrogel markedly reduced cartilage degeneration, joint inflammation, and the loss of the subchondral bone. Taken together, this study provides a potential biomaterial strategy for enhanced OA treatment by delivering the gene-engineered ADSCs within an ECM-mimicking hydrogel.

Pathogenesis of calcium pyrophosphate deposition disease

Calcium pyrophosphate deposition disease is defined by the presence of calcium pyrophosphate (CPP) crystals in articular cartilage and is the fourth most common type of arthritis in adults. Despite its high prevalence, the etiology of CPPD disease remains unclear and no specific therapies currently exist. It has been known for several decades that abnormalities of cartilage pyrophosphate metabolism are common in patients with CPPD disease, and this classic work will be reviewed here. Recent studies of rare familial forms of CPPD disease have provided additional novel information about its pathophysiology. This work suggests that CPPD disease occurs through at least two unique and potentially intertwined biomolecular pathways. We are hopeful that a detailed understanding of the components and regulation of these pathways will lead to improved therapies for this common disease.

The Gasotransmitter Hydrogen Sulfide (H2S) Prevents Pathologic Calcification (PC) in Cartilage

Pathologic calcification (PC) is a painful and disabling condition whereby calcium-containing crystals deposit in tissues that do not physiologically calcify: cartilage, tendons, muscle, vessels and skin. In cartilage, compression and inflammation triggered by PC leads to cartilage degradation typical of osteoarthritis (OA). The PC process is poorly understood and treatments able to target the underlying mechanisms of the disease are lacking. Here we show a crucial role of the gasotransmitter hydrogen sulfide (H₂S) and, in particular, of the H₂S-producing enzyme cystathionine γ-lyase (CSE), in regulating PC in cartilage. Cse deficiency (Cse KO mice) exacerbated calcification in both surgically-induced (menisectomy) and spontaneous (aging) murine models of cartilage PC, and augmented PC was closely associated with cartilage degradation (OA). On the contrary, Cse overexpression (Cse tg mice) protected from these features. In vitro, Cse KO chondrocytes showed increased calcification, potentially via enhanced alkaline phosphatase (Alpl) expression and activity and increased IL-6 production. The opposite results were obtained in Cse tg chondrocytes. In cartilage samples from patients with OA, CSE expression inversely correlated with the degree of tissue calcification and disease severity. Increased cartilage degradation in murine and human tissues lacking or expressing low CSE levels may be accounted for by dysregulated catabolism. We found higher levels of matrix-degrading metalloproteases Mmp-3 and -13 in Cse KO chondrocytes, whereas the opposite results were obtained in Cse tg cells. Finally, by high-throughput screening, we identified a novel small molecule CSE positive allosteric modulator (PAM), and demonstrated that it was able to increase cellular H₂S production, and decrease murine and human chondrocyte calcification and IL-6 secretion. Together, these data implicate impaired CSE-dependent H₂S production by chondrocytes in the etiology of cartilage PC and worsening of secondary outcomes (OA). In this context, enhancing CSE expression and/or activity in chondrocytes could represent a potential strategy to inhibit PC.

Synthesis of Inorganic Pyrophosphatase-Nanodiamond Conjugates Resistant to Calcium and Fluoride

Pyrophosphate arthropathy is the mineralization defect in humans caused by the deposition of microcrystals of calcium pyrophosphate dihydrate in joint tissues. As a potential therapeutic strategy for the treatment of pyrophosphate arthropathy, delivery of exogenous pyrophosphate-hydrolyzing enzymes, inorganic pyrophosphatases (PPases), to the synovial fluid has been suggested. Previously, we synthesized the conjugates of Escherichia coli PPase (Ec-PPase) with detonation synthesis nanodiamonds (NDs) as a delivery platform, obtaining the hybrid biomaterial retaining high pyrophosphate-hydrolyzing activity in vitro. However, most known PPases including Ec-PPase in the soluble form are strongly inhibited by Ca²⁺ ions. Because synovial fluid contains up to millimolar concentrations of soluble calcium, this inhibition might limit the in vivo application of Ec-PPase-based material in joint tissues. In this work, we proposed other bacterial PPases from Mycobacterium tuberculosis (Mt-PPase), which are resistant to the inhibition by Ca²⁺ ions, as an active PP_i-hydrolyzing agent. We synthesized conjugates of Mt-PPase with NDs and tested their activity under various conditions. Unexpectedly, conjugates of both Ec-PPase and Mt-PPase with aminated NDs retained significant hydrolytic activity in the presence of well-known mechanism-based PPase inhibitors, fluoride or calcium. The incomplete inhibition of PPases by fluoride or calcium was found for the first time.

Pathological calcification in osteoarthritis: an outcome or a disease initiator?

In the progression of osteoarthritis, pathological calcification in the affected joint is an important feature. The role of these crystallites in the pathogenesis and progression of osteoarthritis is controversial; it remains unclear whether they act as a disease initiator or are present as a result of joint damage. Recent studies reported that the molecular mechanisms regulating physiological calcification of skeletal tissues are similar to those regulating pathological or ectopic calcification of soft tissues. Pathological calcification takes place when the equilibrium is disrupted. Calcium phosphate crystallites are identified in most affected joints and the presence of these crystallites is closely correlated with the extent of joint destruction. These observations suggest that pathological calcification is most likely to be a disease initiator instead of an outcome of osteoarthritis progression. Inhibiting pathological crystallite deposition within joint tissues therefore represents a potential therapeutic target in the management of osteoarthritis.

BONE MARKERS IN ARTHROPATHIES

Bone endures a lifelong course of construction and destruction, with bone marker (BM) molecules released during this cycle. The field of measuring BM levels in synovial fluid and peripheral blood is a cardinal part of bone research within modern clinical medicine and has developed extensively in the last years. The purpose of our work was to convey an up-to-date overview on synovial fluid and serum BMs in the most common arthropathies.

Vitamin K as a Powerful Micronutrient in Aging and Age-Related Diseases: Pros and Cons from Clinical Studies

Vitamin K is a multifunctional micronutrient implicated in age-related diseases such as cardiovascular diseases, osteoarthritis and osteoporosis. Although vitamin K-dependent proteins (VKDPs) are described to have a crucial role in the pathogenesis of these diseases, novel roles have emerged for vitamin K, independently of its role in VKDPs carboxylation. Vitamin K has been shown to act as an anti-inflammatory by suppressing nuclear factor κB (NF-κB) signal transduction and to exert a protective effect against oxidative stress by blocking the generation of reactive oxygen species. Available clinical evidences indicate that a high vitamin K status can exert a protective role in the inflammatory and mineralization processes associated with the onset and progression of age-related diseases. Also, vitamin K involvement as a protective super-micronutrient in aging and ‘inflammaging’ is arising, highlighting its future use in clinical practice. In this review we summarize current knowledge regarding clinical data on vitamin K in skeletal and cardiovascular health, and discuss the potential of vitamin K supplementation as a health benefit. We describe the clinical evidence and explore molecular aspects of vitamin K protective role in aging and age-related diseases, and its involvement as a modulator in the interplay between pathological calcification and inflammation processes.

Calcium crystal deposition diseases - beyond gout

The most common types of calcium-containing crystals that are associated with joint and periarticular disorders are calcium pyrophosphate dihydrate (CPP) and basic calcium phosphate (BCP) crystals. Several diverse but difficult-to-treat acute and chronic arthropathies and other clinical syndromes are associated with the deposition of these crystals. Although the pathogenic mechanism of calcium crystal deposition is partially understood, much remains to be investigated, as no drug is available to prevent crystal deposition, permit crystal dissolution or specifically target the pathogenic effects that result in the clinical manifestations. In this Review, the main clinical manifestations of CPP and BCP crystal deposition are discussed, along with the biological effects of these crystals, current therapeutic approaches and future directions in therapy.

Emergent nanotherapies in microcrystal-induced arthritis

The anti-inflammatory and immunomodulatory effects of nanoparticles in several chronic diseases have been extensively researched. The aim of this review is to examine how nanoparticles modulate the inflammatory pathways that characterize the most prevalent forms of microcrystal-induced arthritis, including gout, pseudogout, and BCP-induced arthritis. The nanoparticles of chitosan-coated calcium phosphate, uricase, aceclofenac, and gold have been investigated in crystal-inducedarthritis. The most important results of the studies outlined in this review show that nanoparticles can inhibit the expression and the release of some pro-inflammatory mediators and proteolytic enzymes, and the activity of different transcriptional factors in vitro, as well as decrease the uric acid levels in several studies of in vitro and in vivo models of gout, which show interesting results in terms of decreasing the amount of crystals and tissue damage, respectively. In view of their multiple beneficial effects, nanoparticles can be considered a valuable therapy that contributes to the pharmacological treatment in crystalinduced arthritis.

Implication of a novel vitamin K dependent protein, GRP/Ucma in the pathophysiological conditions associated with vascular and soft tissue calcification, osteoarthritis, inflammation, and carcinoma

Gla-rich protein (GRP) or unique cartilage matrix-associated protein (Ucma), the newest member of vitamin K dependent proteins, carries exceptionally high number of γ-carboxyglutamic acid (Gla) residues which contributes to its outstanding capacity of binding with calcium in the extracellular environment indicating its potential role as a global calcium modulator. Recent studies demonstrated a critical function of GRP in the regulation of different pathophysiological conditions associated with vascular and soft tissue calcification including cardiovascular diseases, osteoarthritis, inflammation, and skin and breast carcinomas. These findings established an important relationship between γ-carboxylation of GRP and calcification associated disease pathology suggesting a critical role of vitamin K in the pathophysiological features of various health disorders. This review for the first time summarizes all of the updated findings related to the functional activities of GRP in the pathogenesis of several diseases associated with vascular and soft tissue mineralization, osteoarthritis, inflammation, and carcinoma. The outcome of this review will improve the understanding about the role of GRP in the pathogenesis of tissue calcification and its associated health disorders, which should in turn lead to the design of clinical interventions to improve the condition of patients associated with these health disorders.

Calcium-phosphate complex increased during subchondral bone remodeling affects earlystage osteoarthritis

An activation of osteoclasts and subchondral bone remodeling is a major histologic feature of early-stage osteoarthritis (OA), which can be accompanied by an increase of calcium (Ca) and phosphate (Pi) level in the subchondral milieu. Considering articular cartilage gets most of nutrition from subchondral bone by diffusion, these micro-environmental changes in subchondral bone can affect the physiology of articular chondrocytes. Here, we have shown that Ca is increased and co-localized with Pi in articular cartilage of early-stage OA. The Ca-Pi complex increased the production of MMP-3 and MMP-13 in the hypertrophic chondrocytes, which was dependent on nuclear factor-kappa B (NF-kB), p38 and extracellular signal-regulated kinase (Erk) 1/2 mitogen-activated protein (MAP) kinase and Signal transducer and activator of transcription 3 (STAT3) signaling. The Ca-Pi complexes increased the expression of endocytosis markers, and the inhibition of the formation of the Ca-Pi complex ameliorated the Ca-Pi complex-mediated increases of MMPs expression in hypertrophic chondrocytes. Our data provide insight regarding the Ca-Pi complex as a potential catabolic mediator in the subchondral milieu and support the pathogenic role of subchondral bone in the early stages of cartilage degeneration.

Association of Chondrocalcinosis in Knee Joints With Pain and Synovitis: Data From the Osteoarthritis Initiative

OBJECTIVE

To evaluate the relationship between chondrocalcinosis and pain or synovitis in knee joints by examining data from the Osteoarthritis Initiative (OAI).

METHODS

Data were obtained from the OAI public-use data sets. The relationship between chondrocalcinosis on baseline knee radiograph and pain at baseline and at 4 years was examined. Analyses were adjusted for age, sex, body mass index, and Kellgren-Lawrence (K/L) grade and the correlation between 2 knees in a subject was controlled using generalized estimating equations. The relationship between chondrocalcinosis and synovitis on magnetic resonance imaging (MRI) was examined by comparing knees with chondrocalcinosis at baseline and age, sex, and K/L grade-matched knees with no chondrocalcinosis. We read MRIs of a subset of knees for synovitis using the MRI Osteoarthritis Knee Score (MOAKS) on baseline and 4-year MRI.

RESULTS

Knees with chondrocalcinosis (n = 162) more often had pain compared to knees without chondrocalcinosis (n = 2,030) at baseline and had higher Western Ontario and McMaster Universities Osteoarthritis Index pain scores, both at baseline (mean 2.4 [95% confidence interval (95% CI) 1.9, 2.9]) versus mean 1.8 [95% CI 1.7, 1.9]) and at 4 years (mean 2.5 [95% CI 1.9, 3.1] versus mean 1.6 [95% CI 1.5, 1.8]), as well as higher Intermittent and Constant Osteoarthritis Pain intermittent pain scores at 4 years. There was no difference in MOAKS synovitis scores at baseline and at 4 years between the chondrocalcinosis group (n = 102) and the control group (n = 99).

CONCLUSION

Knees with chondrocalcinosis had increased pain and did not have higher synovitis scores on MRI compared to knees without chondrocalcinosis. The mechanisms by which chondrocalcinosis is associated with increased pain remain to be determined.

Low prevalence of knee chondrocalcinosis and its catabolic association with serum matrix metalloproteinase 3: A rural Japanese population study

AIM

This study aimed to elucidate the prevalence of radiographic knee chondrocalcinosis (CC) and to clarify whether CC is correlated with self-reported knee symptoms and a serum catabolic biomarker.

METHODS

A total of 1278 volunteers participated. Plain radiographs of both knees were obtained. Identification of a linear calcification in the knee joint space was defined as CC. Patients with a Kellgren-Lawrence grade of 2 or more were considered to have knee osteoarthritis (OA). Symptoms were evaluated using the Knee injury and Osteoarthritis Outcome Score (KOOS) Pain scale, and serum matrix metalloproteinase-3 (MMP-3) concentration was determined. Multiple regression analysis was conducted to determine whether CC was correlated with OA, the KOOS Pain scale and MMP-3 concentration.

RESULTS

Twenty-eight subjects were found to have CC (2.2%), and 389 had OA (30.4%). CC was correlated with OA (odds ratio: 5.797; P = 0.006). Additionally, CC was correlated with MMP-3 concentration (B = 11.415, β = 0.059, P = 0.014), but not with KOOS Pain scale.

CONCLUSIONS

The prevalence of CC was low in the Japanese population evaluated in this study. While CC was not correlated with self-reported knee symptoms, it was positively correlated with serum MMP-3 concentration.

Unilateral anterior crossbite induces aberrant mineral deposition in degenerative temporomandibular cartilage in rats

OBJECTIVE

To investigate whether mechanical stress induces mineral deposits that contribute to matrix degradation at the onset of osteoarthritis (OA) in temporomandibular joint (TMJ) cartilage.

DESIGN

Female Spraguee-Dawley rats were subjected to an unilateral anterior crossbite (UAC) procedure. Histology, electron microscopy, and energy dispersive spectrometer (EDS) were used to examine cartilage matrix structures and composition of mineral deposit in the affected TMJ cartilage. Protein and/or RNA expression of phenotypic markers and mineralization modulators and matrix degradation was analyzed by immunohistochemistry and/or real-time PCR. Synthetic basic calcium phosphate (BCP) and calcium pyrophosphate dehydrate (CPPD) crystals were used to stimulate ATDC5 cells for their impact on cell differentiation and gene expression.

RESULTS

Fragmented and disorganized collagen fibers, expanded fibrous spaces, and enhancement of matrix vesicle production and mineral deposition were observed in matrices surrounding hypertrophic chondrocytes in cartilage as early as 2-weeks post-UAC and exacerbated with time. The mineral deposits in TMJ cartilage at 12- and 20-weeks post-UAC had Ca/P ratios of 1.42 and 1.44, which are similar to the ratios for BCP. The expression of mineralization inhibitors, NPP1, ANK, CD73, and Matrix gla protein (MGP) was decreased from 2 to 8 weeks post-UAC, so were the chondrogenic markers, Col-2, Col-X and aggrecan. In contrast, the expression of tissue-nonspecific alkaline phosphatase (TNAP) and MMP13 was increased 4-weeks post-UAC. Treating ADTC5 cells with BCP crystals increased MMPs and ADAMTS5 expression, but reduced matrix production in a time-dependent manner.

CONCLUSION

UAC induces deposition of BCP-like minerals in osteoarthritic cartilage, which can stimulate matrix degradation by promoting the expression of cartilage-degrading enzymes to facilitate OA progression.

Inflammatory mediators in osteoarthritis: A critical review of the state-of-the-art, current prospects, and future challenges

Osteoarthritis (OA) has traditionally been defined as a prototypical non-inflammatory arthropathy, but today there is compelling evidence to suggest that it has an inflammatory component. Many recent studies have shown the presence of synovitis in a large number of patients with OA and demonstrated a direct association between joint inflammation and the progression of OA. Pro-inflammatory cytokines, reactive oxygen species (ROS), nitric oxide, matrix degrading enzymes and biomechanical stress are major factors responsible for the progression of OA in synovial joints. The aim of this review is to discuss the significance of a wide range of implicated inflammatory mediators and their contribution to the progression of OA. We also discuss some of the currently available guidelines, practices, and prospects. In addition, this review argues for new innovation in methodologies and instrumentation for the non-invasive detection of inflammation in OA by modern imaging techniques. We propose that identifying early inflammatory events and targeting these alterations will help to ameliorate the major symptoms such as inflammation and pain in OA patients.

Gla-rich protein is involved in the cross-talk between calcification and inflammation in osteoarthritis

Osteoarthritis (OA) is a whole-joint disease characterized by articular cartilage loss, tissue inflammation, abnormal bone formation and extracellular matrix (ECM) mineralization. Disease-modifying treatments are not yet available and a better understanding of osteoarthritis pathophysiology should lead to the discovery of more effective treatments. Gla-rich protein (GRP) has been proposed to act as a mineralization inhibitor and was recently shown to be associated with OA in vivo. Here, we further investigated the association of GRP with OA mineralization-inflammation processes. Using a synoviocyte and chondrocyte OA cell system, we showed that GRP expression was up-regulated following cell differentiation throughout ECM calcification, and that inflammatory stimulation with IL-1β results in an increased expression of COX2 and MMP13 and up-regulation of GRP. Importantly, while treatment of articular cells with γ-carboxylated GRP inhibited ECM calcification, treatment with either GRP or GRP-coated basic calcium phosphate (BCP) crystals resulted in the down-regulation of inflammatory cytokines and mediators of inflammation, independently of its γ-carboxylation status. Our results strengthen the calcification inhibitory function of GRP and strongly suggest GRP as a novel anti-inflammatory agent, with potential beneficial effects on the main processes responsible for osteoarthritis progression. In conclusion, GRP is a strong candidate target to develop new therapeutic approaches.

Crystal structure of monoclinic calcium pyrophosphate dihydrate (m-CPPD) involved in inflammatory reactions and osteoarthritis

Pure monoclinic calcium pyrophosphate dihydrate (m-CPPD) has been synthesized and characterized by synchrotron powder X-ray diffraction and neutron diffraction. Rietveld refinement of complementary diffraction data has, for the first time, allowed the crystal structure of m-CPPD to be solved. The monoclinic system P2(1)/n was confirmed and unit-cell parameters determined: a = 12.60842 (4), b = 9.24278 (4), c = 6.74885 (2) Å and β = 104.9916 (3)°. Neutron diffraction data especially have allowed the precise determination of the position of H atoms in the structure. The relationship between the m-CPPD crystal structure and that of the triclinic calcium pyrophosphate dihydrate (t-CPPD) phase as well as other pyrophosphate phases involving other divalent cations are discussed by considering the inflammatory potential of these phases and/or their involvement in different diseases. These original structural data represent a key step in the understanding of the mechanisms of crystal formation involved in different types of arthritis and to improve early detection of calcium pyrophosphate (CPP) phases in vivo.

From crystalline to amorphous calcium pyrophosphates: A solid state Nuclear Magnetic Resonance perspective

Hydrated calcium pyrophosphates (CPP, Ca2P2O7·nH2O) are a fundamental family of materials among osteoarticular pathologic calcifications. In this contribution, a comprehensive multinuclear NMR (Nuclear Magnetic Resonance) study of four crystalline and two amorphous phases of this family is presented. (1)H, (31)P and (43)Ca MAS (Magic Angle Spinning) NMR spectra were recorded, leading to informative fingerprints characterizing each compound. In particular, different (1)H and (43)Ca solid state NMR signatures were observed for the amorphous phases, depending on the synthetic procedure used. The NMR parameters of the crystalline phases were determined using the GIPAW (Gauge Including Projected Augmented Wave) DFT approach, based on first-principles calculations. In some cases, relaxed structures were found to improve the agreement between experimental and calculated values, demonstrating the importance of proton positions and pyrophosphate local geometry in this particular NMR crystallography approach. Such calculations serve as a basis for the future ab initio modeling of the amorphous CPP phases.

STATEMENT OF SIGNIFICANCE

The general concept of NMR crystallography is applied to the detailed study of calcium pyrophosphates (CPP), whether hydrated or not, and whether crystalline or amorphous. CPP are a fundamental family of materials among osteoarticular pathologic calcifications. Their prevalence increases with age, impacting on 17.5% of the population after the age of 80. They are frequently involved or associated with acute articular arthritis such as pseudogout. Current treatments are mainly directed at relieving the symptoms of joint inflammation but not at inhibiting CPP formation nor at dissolving these crystals. The combination of advanced NMR techniques, modeling and DFT based calculation of NMR parameters allows new original insights in the detailed structural description of this important class of biomaterials.

Structure of the calcium pyrophosphate monohydrate phase (Ca2P2O7·H2O): towards understanding the dehydration process in calcium pyrophosphate hydrates

Calcium pyrophosphate hydrate (CPP, Ca(2)P(2)O(7) · nH2O) and calcium orthophosphate compounds (including apatite, octacalcium phosphate etc.) are among the most prevalent pathological calcifications in joints. Even though only two dihydrated forms of CPP (CPPD) have been detected in vivo (monoclinic and triclinic CPPD), investigations of other hydrated forms such as tetrahydrated or amorphous CPP are relevant to a further understanding of the physicochemistry of those phases of biological interest. The synthesis of single crystals of calcium pyrophosphate monohydrate (CPPM; Ca(2)P(2)O(7) · H2O) by diffusion in silica gel at ambient temperature and the structural analysis of this phase are reported in this paper. Complementarily, data from synchrotron X-ray diffraction on a CPPM powder sample have been fitted to the crystal parameters. Finally, the relationship between the resolved structure for the CPPM phase and the structure of the tetrahydrated calcium pyrophosphate β phase (CPPT-β) is discussed.

Insights into the association of Gla-rich protein and osteoarthritis, novel splice variants and γ-carboxylation status

SCOPE

Gla-rich protein (GRP) is a vitamin K dependent protein, characterized by a high density of γ-carboxylated Glu residues, shown to accumulate in mouse and sturgeon cartilage and at sites of skin and vascular calcification in humans. Therefore, we investigated the involvement of GRP in pathological calcification in osteoarthritis (OA).

METHODS AND RESULTS

Comparative analysis of GRP patterning at transcriptional and translational levels was performed between controls and OA patients. Using a RT-PCR strategy we unveiled two novel splice variants in human-GRP-F5 and F6-potentially characterized by the loss of full γ-carboxylation and secretion functional motifs. GRP-F1 is shown to be the predominant splice variant expressed in mouse and human adult tissues, particularly in OA cartilage, while an overexpressing human cell model points it as the major γ-carboxylated isoform. Using validated conformational antibodies detecting carboxylated or undercarboxylated GRP (c/uc GRP), we have demonstrated cGRP accumulation in controls, whereas ucGRP was the predominant form in OA-affected tissues, colocalizing at sites of ectopic calcification.

CONCLUSION

Overall, our results indicate the predominance of GRP-F1, and a clear association of ucGRP with OA cartilage and synovial membrane. Levels of vitamin K should be further assessed in these patients to determine its potential therapeutic use as a supplement in OA treatment.

Deleterious effects of osteoarthritis on the structure and function of the meniscal enthesis

OBJECTIVE

The ability of menisci to prevent osteoarthritis (OA) is dependent on the integrity of the complex meniscal entheses, the attachments of the menisci to the underlying subchondral bone (SB). The goal of this study was to determine mechanical and structural changes in meniscal entheses after the onset of OA.

DESIGN

Healthy and osteoarthritic meniscal entheses were evaluated for changes in histomorphological characteristics, mineralization, and mechanical properties. Glycosaminoglycans (GAG) and calcium in the insertion were evaluated with histological staining techniques. The extent of calcium deposition was assessed and tidemark (TM) integrity was quantified. Changes in the mineralized zone of the insertion were examined using micro-computed tomography (μCT) to determine bone mineral density, cortical zone thickness, and mineralization gradient. Mechanical properties of the entheses were measured using nano-indentation techniques to obtain material properties based on viscoelastic analysis.

RESULTS

GAG thickness in the calcified fibrocartilage (CFC) zone and calcium content were significantly greater in osteoarthritic anterior meniscal entheses. TM integrity was significantly decreased in OA tissue, particularly in the medial anterior (MA) enthesis. The mineralized zone of osteoarthritic meniscal entheses was significantly thicker than in healthy entheses and showed decreased bone mineral density. Fitting of mineralization data to a sigmoidal Gompertz function revealed a lower rate of increase in mineralization in osteoarthritic tissue. Analysis of viscoelastic mechanical properties revealed increased compliance in osteoarthritic tissue.

CONCLUSIONS

These data suggest that significant changes occur at meniscal enthesis sites with the onset of OA. Mechanical and structural changes in meniscal entheses may contribute to meniscal extrusion, which has been shown to increase the progression of OA.

Follow-up study of inflammatory ultrasound features in hand osteoarthritis over a period of 3 months: variable as well as constant

OBJECTIVE

To study inflammatory ultrasound (US) features and pain over a 3-month period in hand osteoarthritis (HOA).

DESIGN

In 25 consecutive HOA patients (mean age 60 years, 76% female), fulfilling the American College of Rheumatology (ACR) criteria, visual analogue scale (VAS) pain scores were collected at baseline and 3 months. In 750 [all first carpometacarpal (CMC), metacarpalphalangeal (MCP), proximal interphalangeal (PIP), distal interphalangeal (DIP) and first interphalangeal (IP)] joints, pain was assessed upon palpation and synovial thickening, effusion and power Doppler signal (PDS) were scored with standardized methods by US. Associations between inflammatory features and painful joints were analysed using generalized estimated equations to account for patient effects, adjusting for confounders, and presented as odds ratios (ORs) with 95% confidence intervals (95%CI).

RESULTS

Inflammatory US features were seen in (nearly) all patients. The median number (range) of inflammatory joints per patient did not change over time: 9 (0-16) to 9 (2-18). In 18.7% of joints inflammatory features were present at both time points; in 20.5% inflammatory features occurred only at baseline or follow-up. Pain decreased over time: median VAS pain 49-39 mm; median number of painful joints 8-3. Synovial thickening, effusion and PDS were associated with pain upon palpation both at baseline and follow-up: OR 2.9 (1.4, 5.7), 2.7 (1.7, 4.3), 3.6 (2.1, 6.3) and 7.3 (3.2, 16.5), 3.3 (2.3, 4.7), 4.1 (2.1, 7.9). respectively.

CONCLUSIONS

In HOA inflammatory US features are stable over time at patient level, but vary on joint level. Pain diminished after 3 months, while associations between painful joints and inflammation seem to increase, emphasizing the multifactorial aetiology of pain.

Crystal suspensions of poorly soluble peptides for intra-articular application: a novel approach for biorelevant assessment of their in vitro release

Crystal suspensions of 3 poorly soluble peptides (MSC1, 2 and 3), intended for intra-articular administration were prepared and in vitro release was tested by a modified USP IV apparatus, combined with a dialysis system. Half-lives of release profiles were ∼5 days for MSC1 and ∼0.5 days for MSC2 and MSC3, showing the potential to achieve sustained exposure from crystal suspensions after intra-articular administration. The in vitro release setup discriminated between (i) different formulations, (ii) different concentrations of API and (iii) different APIs. In addition it was shown that this method allows the modification of release conditions in order to gain more biorelevance for in vitro release testing in the field of intra-articular application: the influence of synovial fluid components hyaluronic acid and albumin was demonstrated, showing prolonged half-lives for suspensions containing 2.5% bovine serum albumin (5 days) and accelerated release rates for suspensions containing 1% sodium hyaluronate (2.5 days) in comparison to a suspension in phosphate buffered saline (4 days). Furthermore, it was demonstrated that release rates of a suspension containing an artificial synovial fluid were in accordance with suspensions containing bovine synovial fluid (t1/2∼4 days).

Diagnosis and clinical presentation of osteoarthritis

Osteoarthritis (OA), the commonest arthropathy, targets the knees, hips, finger interphalangeal joints, thumb bases, first metatarsophalangeal joints, and spinal facet joints, and displays marked heterogeneity of clinical presentation. Signs of OA include coarse crepitus, bony enlargement, reduced range of movement, and joint-line tenderness. Muscle wasting and joint deformity occur with severe OA. Painful periarticular disorders often coexist with OA. Inflammation is absent or only modest, although mild-moderate effusions are common at the knee. The diagnosis of OA may be made without recourse to radiographic or laboratory investigations in the at-risk age group with typical symptoms and signs.

Mechanisms involved in suppression of ADAMTS4 expression in synoviocytes by high molecular weight hyaluronic acid

Aggrecan degradation is considered to play a key role in the progression of osteoarthritis (OA). Aggrecanases are members of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) family, and degrade aggrecan in OA cartilage. The aim of this study was to clarify the mechanisms of expression of ADAMTS4 induced by IL-1β in human fibroblast-like synoviocyte (HFLS) cells by high molecular weight hyaluronan (HMW-HA), a therapeutic agent used for OA. Monolayer cultures of HFLS cells were incubated with IL-1β and HMW-HA. In some experiments, cells were pretreated with the CD44 function-blocking monoclonal antibody or inhibitors of signaling pathways prior to addition of IL-1β and HMW-HA. The expressions of ADAMTS4 mRNA and protein were monitored using real-time RT-PCR, Western blotting, and immunofluorescence microscopy. To further determine the role of HMW-HA in IL-1β-induced ADAMTS4 expression, activation of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-jun NH2-terminal kinase (JNK), Akt, and NF-κB were analyzed by Western blotting. HMW-HA suppressed ADAMTS4 mRNA and protein expressions induced by IL-1β. Pretreatment with the anti-CD44 monoclonal antibody recovered the inhibitory effect of HMW-HA on expression of ADAMTS4 mRNA induced by IL-1β. Western blotting analysis revealed that IL-1β-induced phosphorylation of p38 MAPK and JNK protein were diminished by HMW-HA. Furthermore, inhibition of the p38 MAPK and JNK pathways by chemical inhibitors suppressed ADAMTS4 mRNA expression stimulated by IL-1β. These results suggest that HMW-HA plays an important role as a regulatory factor in synovial tissue inflammation.

Chondrocalcinosis of femoro-tibial and proximal tibio-fibular joints in cadaveric specimens: a high-resolution CT imaging study of the calcification distribution

Objectives

To analyze calcium deposits by computed tomography (CT) in femoro-tibial compartments and proximal tibio-fibular joints; to assess the relationship with CT-assessed osteoarthritis (OA).

Methods

68 (34 pairs) cadaveric knees (mean age of 84) were scanned at high resolution CT. Menisci and hyaline cartilage calcifications in the femoro-tibial and proximal tibio-fibular joints were analyzed. OA was CT-assessed by the Kellgren and Lawrence score. Gross appearance of OA was evaluated on 29 left knees after dissection and India ink staining of tibial plateaus.

Results

In femoro-tibial joints, meniscal calcifications (MC) and hyaline cartilage calcifications (HCC) were detected in 23(34%) and 14(21%) knees respectively. Calcifications mainly involved the three meniscal segments and were mainly observed in all thirds of the femoro-tibial compartments. In proximal tibio-fibular joints, HCC were detected in 19(28%) knees. The association HCC-MC in femoro-tibial joints and between calcifications in femoro-tibial and proximal tibio-fibular joints was strong (p<0.0001). Femoro-tibial and proximal tibio-fibular CT-assessed OA were respectively found in 23(34%) and 19(28%) knees. HCC were significantly associated with femoro-tibial OA (p = 0.04) while MC were not (p = 0.34). OA macroscopic evaluation showed a mean surface of cartilage lesions of 35% (range 0.13–0.55). No significant difference was demonstrated regarding the CT-detection of MC, HCC or CT-assessed OA.

Conclusions

This is the first study to report a strong association of chondrocalcinosis between femoro-tibial and tibio-fibular joints in addition to a strong association between MC and HCC in femoro-tibial compartments. No significant relationship between chondrocalcinosis and OA was demonstrated.

Pathophysiology of articular chondrocalcinosis--role of ANKH

Calcium pyrophosphate (CPP) crystal deposition (CPPD) is associated with ageing and osteoarthritis, and with uncommon disorders such as hyperparathyroidism, hypomagnesemia, hemochromatosis and hypophosphatasia. Elevated levels of synovial fluid pyrophosphate promote CPP crystal formation. This extracellular pyrophosphate originates either from the breakdown of nucleotide triphosphates by plasma-cell membrane glycoprotein 1 (PC-1) or from pyrophosphate transport by the transmembrane protein progressive ankylosis protein homolog (ANK). Although the etiology of apparent sporadic CPPD is not well-established, mutations in the ANK human gene (ANKH) have been shown to cause familial CPPD. In this Review, the key regulators of pyrophosphate metabolism and factors that lead to high extracellular pyrophosphate levels are described. Particular emphasis is placed on the mechanisms by which mutations in ANKH cause CPPD and the clinical phenotype of these mutations is discussed. Cartilage factors predisposing to CPPD and CPP-crystal-induced inflammation and current treatment options for the management of CPPD are also described.

The role of uric acid and other crystals in osteoarthritis

Clinicians have long assumed that an association exists between crystal arthropathies and the presence of osteoarthritis (OA). However, studies establishing an independent association between calcium pyrophosphate or uric acid crystal disease and OA are sparse. Even less is known about a possible pathogenic relationship. Whereas some studies suggest that the relationships between crystals and OA may not be incidental and that crystal deposition may contribute to the onset and/or acceleration of OA joint damage, other authors have challenged this assertion. In this review, we provide an overview of past and current research elucidating the role of crystal deposition, including monosodium urate, calcium pyrophosphate, and other crystals, in OA. Given the clinical frequency of gout and that agents exist to modulate serum UA levels, special attention is given to the role of monosodium urate crystals.

Expression and functional role of adenosine receptors in regulating inflammatory responses in human synoviocytes

BACKGROUND AND PURPOSE

Adenosine is an endogenous modulator, interacting with four G-protein coupled receptors (A(1), A(2A), A(2B) and A(3)) and acts as a potent inhibitor of inflammatory processes in several tissues. So far, the functional effects modulated by adenosine receptors on human synoviocytes have not been investigated in detail. We evaluated mRNA, the protein levels, the functional role of adenosine receptors and their pharmacological modulation in human synoviocytes.

EXPERIMENTAL APPROACH

mRNA, Western blotting, saturation and competition binding experiments, cyclic AMP, p38 mitogen-activated protein kinases (MAPKs) and nuclear factor (NF)-kappaB activation, tumour necrosis factor alpha (TNF-alpha) and interleukin-8 (IL-8) release were assessed in human synoviocytes isolated from patients with osteoarthritis.

KEY RESULTS

mRNA and protein for A(1), A(2A), A(2B) and A(3) adenosine receptors are expressed in human synoviocytes. Standard adenosine agonists and antagonists showed affinity values in the nanomolar range and were coupled to stimulation or inhibition of adenylyl cyclase. Activation of A(2A) and A(3) adenosine receptors inhibited p38 MAPK and NF-kappaB pathways, an effect abolished by selective adenosine antagonists. A(2A) and A(3) receptor agonists decreased TNF-alpha and IL-8 production. The phosphoinositide 3-kinase or G(s) pathways were involved in the functional responses of A(3) or A(2A) adenosine receptors. Synoviocyte A(1) and A(2B) adenosine receptors were not implicated in the inflammatory process whereas stimulation of A(2A) and A(3) adenosine receptors was closely associated with a down-regulation of the inflammatory status.

CONCLUSIONS AND IMPLICATIONS

These results indicate that A(2A) and A(3) adenosine receptors may represent a potential target in therapeutic modulation of joint inflammation.