Acceleration of experimental lapine osteoarthritis by calcium pyrophosphate microcrystalline synovitis

Crystal arthropathies and osteoarthritis-where is the link?

Osteoarthritis (OA) is one of the leading causes of disability worldwide. As our understanding of OA progressively has moved from a purely mechanical "wear and tear" concept toward a complex multi-tissue condition in which inflammation plays a central role, the possible role of crystal-induced inflammation in OA incidence and progression may be relevant. In addition to gout, which affects 4% of the US population, basic calcium phosphate and calcium pyrophosphate deposition both may induce joint inflammation and may play a role in pain in OA. This narrative review article discusses the possible mechanisms underlying the associations between crystal-induced arthropathies and OA, and the important implications of these for clinical practice and future research.

Case Report: Posterolateral Epidural Supra-C2-Root Approach (PESCA) for Biopsy of a Retro-Odontoid Lesions in Same Sitting After Occipitocervical Fixation and Decompression in a Case of Crowned Dens Syndrome With Brainstem Compression and Displacement

Background

‘Crowned dens syndrome' (CDS) is a special form of calcium pyrophosphate dihydrate deposition disease which is characterized radiologically by a halo-like or crown-like distribution in the periodontoid region and clinically by cervical pain. Herein, we will describe our experience of posterolateral epidural supra-C2-root approach (PESCA) for biopsy of retro-odontoid lesions in one surgical session after occipitocervical fixation and decompression in a patient with CDS and massive brainstem compression.

Case Presentation

A 70-year-old woman presented to our department with a 4-week history of progressive walking impairment, neck pain, neck rigidity, fever, dizziness, slight palsy of the left hand, and multiple fall episodes. Magnetic resonance imaging (MRI) of the craniovertebral junction (CVJ) and cervical spine revealed a lesion of the odontoid process and the retro-odontoid region with mainly solid components, as well as small cystic components, and brainstem compression and displacement. In first step, fusion surgery of the CVJ C0–C4 was performed with occiptocervical decompression. After fusion and decompression the lower lateral part of the C1 arc and the lateral superior part of the left side of the C2 arc were removed. The entry point was located directly above the superior part of the C2 root. A biopsy of the lateral portions of the lesions was obtained by bioptic forceps under microscope guidance. Pathologic examination of the mass revealed deposition of birefringent crystals compatible with calcium pyrophosphate. In addition to the clinical symptoms (especially neck pain), the diagnosis of CDS was made. Non-steroidal inflammatory drugs (NSAIDs) and colchicine (and later magnesium) were started. At follow-up examination 6 months after surgery, an MRI scan of the cervical spine revealed regression of the pannus and the cyst with replacement of the brainstem, clinical improvement of walking, and increased strength of the left hand.

Conclusions

This study demonstrates that PESCA can be used to obtain tissue for pathological analysis in one surgical sitting after fusion and decompression and that fusion, decompression, and PESCA (in the same session) together with subsequent conservative management could be a good alternative for the treatment of CDS.

There is no difference in postoperative pain, function and complications in patients with chondrocalcinosis in the outcome of total knee arthroplasty for end-stage osteoarthritis

PURPOSE

Chondrocalcinosis is the radiographic appearance of calcium crystals in cartilage and other soft tissue. It is suggested that preoperative chondrocalcinosis predicts a worse outcome after total knee arthroplasty and it is unclear if chondrocalcinosis leads to more postoperative complications. This study aimed to compare function, pain, postoperative complications, postoperative signs of acute arthritis and revision rates between patients with and without chondrocalcinosis undergoing total knee arthroplasty for osteoarthritis.

METHODS

In this retrospective cohort study performed in 2017, 408 knees in 392 patients (16 bilateral total knee arthroplasties) were included. None of the patients received additional synovectomy. PROMs were evaluated after 1 year (n = 294) and 5 years (n = 308). The follow-up for clinical data was 5 years (n = 408). The range of final follow-up was 57-84 months. All preoperative radiographs were scored for chondrocalcinosis and Oxford Knee Score, Knee Society Score and Algofunctional Index were used to assess outcome. All clinical records were screened for postoperative complications (excessive wound discharge, infection, loosening, PAO, stiffness), arthritis after surgery and reoperation or revision for any reason.

RESULTS

Sixty-three knees (15.4%) showed signs of chondrocalcinosis. Male gender, higher age and lower BMI were risk factors for chondrocalcinosis. No difference was found in Oxford Knee Score, Knee Society Score and Algofunctional Index, nor in postoperative complications, postoperative signs of acute arthritis and revision rate.

CONCLUSION

Patients with and without chondrocalcinosis have the same outcome after total knee arthroplasty related to pain, functionality, complications, arthritis and revision after surgery for end-stage osteoarthritis. Chondrocalcinosis is not a contraindication for total knee arthroplasty and additional synovectomy is unnecessary.

LEVEL OF EVIDENCE

III.

Arthroscopic diagnosis and medical management of calcium pyrophosphate deposition disease in the temporomandibular joint

Calcium pyrophosphate deposition disease (CPPD) is a crystal arthropathy that can involve the temporomandibular joint. It is known to accelerate the osteoarthritic process, often initially presenting with advanced level of disease. The management of CPPD in the rheumatology and orthopedic literature is one of early diagnosis and medical management of acute attacks. The cases of three patients who presented with initial complaints of joint pain and limited mouth opening are presented. Preoperative imaging identified calcifications in two of these patients. Definitive diagnosis was achieved through arthroscopic-assisted biopsy. Rheumatology referrals revealed chondrocalcinosis of the knee in one patient. All patients had improved mouth opening and pain.

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.

Effects of carrageenan induced synovitis on joint damage and pain in a rat model of knee osteoarthritis

OBJECTIVE

Knee osteoarthritis (OA) is associated with ongoing pain and joint damage that can be punctuated by acute flares of pain and inflammation. Synovitis in normal knees might resolve without long-term detriment to joint function. We hypothesised that osteoarthritis is associated with impaired resilience to inflammatory flares.

DESIGN

We induced synovitis by injecting carrageenan into rat knees with or without meniscal transection (MNX)-induced OA, and measured synovitis, weightbearing asymmetry (pain behaviour), and joint damage up to 35 days after OA induction (23 days after carrageenan-injection).

RESULTS

Carrageenan injection induced weightbearing asymmetry for 1 week, transient increase in knee diameter for 2 days, and a sustained increase in synovial macrophages, endothelial cell proliferation and vascular density compared with naive vehicle-injected controls. MNX surgery induced weightbearing asymmetry and histological evidence of OA. Carrageenan-injection in MNX-operated knees was followed for 2 days by increased weightbearing asymmetry compared either to MNX+vehicle or to sham+carrageenan groups. OA structural damage and synovitis at day 35 were greater in MNX+carrageenan compared to MNX+vehicle and sham+carrageenan groups. Carrageenan injection did not induce OA in Sham-operated knees.

CONCLUSION

Intra-articular injection of the pro-inflammatory compound carrageenan in OA and sham-operated control knees induced a short term increase in joint pain. Even though pain flares resolved in both groups and damage was not induced in sham-operated knees, carrageen injection exacerbated long-term joint damage in OA knees. OA knees display less resilience to inflammatory episodes. Preventing inflammatory flares may be particularly important in preventing symptoms and long term joint damage in OA.

Calcium-Containing Crystals and Osteoarthritis: an Unhealthy Alliance

PURPOSE OF REVIEW

Osteoarthritis (OA) is the most common form of joint disease globally and is associated with significant morbidity and disability. Increasing evidence points to an important inflammatory component in the development and progression of OA. The precise pathways involved in OA inflammatory processes remain to be clarified. Basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate (CPP) crystals can induce inflammation and arthritis and recent studies point to a potential pathogenic role in OA. In the light of this evidence, we explore the relationship and potential mechanistic pathways linking calcium-containing crystals and OA.

RECENT FINDINGS

CPP crystals induce inflammation through the NLRP3 inflammasome while BCP crystals mediate both NLRP3 dependent and independent effects. BCP crystals have been demonstrated to induce key mitogenic and inflammatory pathways and contribute to cartilage degradation. Calcium-containing crystals induce key inflammatory pathways and may represent an attractive novel target in OA, a condition devoid of effective treatments.

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.

The structural consequences of calcium crystal deposition

Calcium pyrophosphate dihydrate and basic calcium phosphate (BCP) crystals are the most common calcium-containing crystals associated with rheumatic disease. Clinical manifestations of calcium crystal deposition include acute or chronic inflammatory and degenerative arthritides and certain forms of periarthritis. The intra-articular presence of BCP crystals correlates with the degree of radiographic degeneration. Calcium crystal deposition contributes directly to joint degeneration. Vascular calcification is caused by the deposition of calcium hydroxyapatite crystals in the arterial intima. These deposits may contribute to local inflammation and promote further calcification, thus aggravating the atherosclerotic process. Calcium crystal deposition results in substantial structural consequence in humans.

Pathogenic role of basic calcium phosphate crystals in destructive arthropathies

BACKGROUND

basic calcium phosphate (BCP) crystals are commonly found in osteoarthritis (OA) and are associated with cartilage destruction. BCP crystals induce in vitro catabolic responses with the production of metalloproteases and inflammatory cytokines such as interleukin-1 (IL-1). In vivo, IL-1 production induced by BCP crystals is both dependant and independent of NLRP3 inflammasome. We aimed to clarify 1/ the role of BCP crystals in cartilage destruction and 2/ the role of IL-1 and NLRP3 inflammasome in cartilage degradation related to BCP crystals.

METHODOLOGY PRINCIPAL FINDINGS

synovial membranes isolated from OA knees were analysed by alizarin Red and FTIR. Pyrogen free BCP crystals were injected into right knees of WT, NLRP3 -/-, ASC -/-, IL-1α -/- and IL-1β-/- mice and PBS was injected into left knees. To assess the role of IL-1, WT mice were treated by intra-peritoneal injections of anakinra, the IL-1Ra recombinant protein, or PBS. Articular destruction was studied at d4, d17 and d30 assessing synovial inflammation, proteoglycan loss and chondrocyte apoptosis. BCP crystals were frequently found in OA synovial membranes including low grade OA. BCP crystals injected into murine knee joints provoked synovial inflammation characterized by synovial macrophage infiltration that persisted at day 30, cartilage degradation as evidenced by loss of proteoglycan staining by Safranin-O and concomitant expression of VDIPEN epitopes, and increased chondrocyte apoptosis. BCP crystal-induced synovitis was totally independent of IL-1α and IL-1β signalling and no alterations of inflammation were observed in mice deficient for components of the NLRP3-inflammasome, IL-1α or IL-1β. Similarly, treatment with anakinra did not prevent BCP crystal effects. In vitro, BCP crystals elicited enhanced transcription of matrix degrading and pro-inflammatory genes in macrophages.

CONCLUSIONS SIGNIFICANCE

intra-articular BCP crystals can elicit synovial inflammation and cartilage degradation suggesting that BCP crystals have a direct pathogenic role in OA. The effects are independent of IL-1 and NLRP3 inflammasome.

Treatment and management of pseudogout: insights for the clinician

Pseudogout and the associated calcium pyrophosphate dihydrate (CPPD)- crystal-related arthropathies are common conditions that present particular management problems in clinical practice as they often affect older patients with multiple medical comorbidities. The epidemiology, metabolic and endocrine disease associations, and routine investigations used in the diagnostic workup are briefly reviewed. Current treatment approaches that are mainly directed at relieving the symptoms of joint inflammation are outlined. Unlike gout, there are no agents available that have been shown to decrease crystal load in CPPD-related joint disease. Recent novel insights into the pathogenesis of crystal-induced joint inflammation and subsequent joint degeneration are also discussed. The potential of colchicine as a prophylactic agent in managing recurrent attacks and the likely mechanisms of its effects on the NACHT, LRR and PYD domains-containing protein 3 (NALP-3) inflammasome of the innate immune system are highlighted. The use of agents that directly target the inflammasome, in particular drugs which inhibit the interleukin 1 pathway, in the treatment of severe, refractory pseudogout is also discussed. Finally, there is particular emphasis on the likely pathogenic role of CPPD crystal deposition in degenerative joint disease and the use of targeted anticrystal therapies as potential disease-modifying drugs.

Calcifications in human osteoarthritic articular cartilage: ex vivo assessment of calcium compounds using XANES spectroscopy

Calcium (Ca(2+))-containing crystals (CCs), including basic Ca(2+) phosphate (BCP) and Ca(2+) pyrophosphate dihydrate (CPPD) crystals, are associated with severe forms of osteoarthritis (OA). Growing evidence supports a role for abnormal articular cartilage mineralization in the pathogenesis of OA. However, the role of Ca(2+) compounds in this mineralization process remains poorly understood. Six patients, who underwent total knee joint replacement for primary OA, have been considered in this study. Cartilage from femoral condyles and tibial plateaus in the medial and lateral compartments was collected as 1 mm-thick slices cut tangentially to the articular surface. First, CCs presence and biochemical composition were assessed using Fourier transform infrared spectroscopy (FT-IR). Next, Ca(2+) compound biochemical form was further assessed using X-ray absorption spectroscopy (XAS) performed at the Ca(2+) K-absorption edge. Overall, 12 cartilage samples were assessed. Using FT-IR, BCP and CPPD crystals were detected in four and three out of 12 samples, respectively. Ca(2+) compound biochemical forms differed between areas with versus without CCs, when compared using XAS. The complete set of data shows that XANES spectroscopy can be used to accurately characterize sparse CCs in human OA cartilage. It is found that Ca(2+) compounds differ between calcified and non-calcified cartilage areas. In calcified areas they appear to be mainly involved in calcifications, namely Ca(2+) crystals.

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.

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

OBJECTIVES

The role of calcium phosphate and pyrophosphate crystals in osteoarthritis (OA) is unclear: are they a symptom of the damage that occurs to the joint or a key intermediate in the progression of inflammation and joint damage that occurs in OA? The proinflammatory and catabolic response of synthetic calcium phosphate and pyrophosphate crystals and crystals extracted from human osteoarthritic knee cartilage has been investigated. The crystal forms eliciting a response have been characterised allowing a comparison of the biological effects of synthetic and native calcium crystals on human osteoarthritic chondrocytes and synoviocytes to be carried out.

METHODS

Calcium phosphate and pyrophosphate crystals were synthesised in vitro and their crystal forms characterised by X-ray powder diffraction (XRPD). The inorganic crystalline material present in human osteoarthritic cartilage was extracted and its structural composition elucidated by XRPD. These crystals were applied to human primary osteoarthritic chondrocytes and synoviocytes and the production of proinflammatory and catabolic mediators measured.

RESULTS

The crystals extracted from human osteoarthritic knee cartilage were identified as consisting of a mixture of monoclinic and triclinic calcium pyrophosphate dihydrate (m-CPPD and t-CPPD). These crystals elicited an inflammatory and catabolic response in human primary osteoarthritic chondrocytes and synoviocytes as measured by an increase in nitric oxide (NO), matrix metalloproteinase 13 (MMP-13) and prostaglandin E2 (PGE(2)) production. NO, MMP-13 and PGE(2) production was also increased when the synthetic calcium hydrogen phosphate dihydrate (DCPD) and calcium pyrophosphate hydrates were applied to the cells.

CONCLUSIONS

Crystals extracted from human osteoarthritic knee cartilage induce the production of proinflammatory and catabolic mediators (NO, MMP-13 and PGE(2)) in human primary chondrocytes and synoviocytes. Synthetic calcium phosphate and pyrophosphate crystals elicit a similar response in those cells. Our findings suggest that these crystals could contribute to cartilage degradation and synovitis in OA.

Advances in understanding calcium-containing crystal disease

PURPOSE OF REVIEW

Calcium pyrophosphate dihydrate and basic calcium phosphate crystals are the two most common calcium-containing crystals involved in rheumatic diseases. Recent literature concerning their role in the pathogenesis of osteoarthritis is reviewed.

RECENT FINDINGS

In some instances, these calcium crystals might worsen osteoarthritis cartilage destruction. Laboratory investigations have identified determinants of cartilage calcification, especially a better characterization of matrix vesicle content and a better understanding of the regulation of inorganic pyrophosphate and phosphate concentration. In-vitro studies have highlighted new pathogenic mechanisms of calcium crystal-induced cell activation. Several intracellular signalling pathways are activated by calcium crystals. Recent studies suggested the implication of the inflammasome complex and a pivotal role for IL-1 in pseudogout attacks and chondrocyte apoptosis in basic calcium phosphate crystal-related arthropathies.

SUMMARY

Animal models of osteoarthritis and in-vitro studies using calcium pyrophosphate dihydrate and basic calcium phosphate crystals will improve our knowledge of these common crystals and could suggest new targets for drugs, as these common diseases are 'orphan' with respect to therapy.

Point: Hydroxyapatite crystal deposition is intimately involved in the pathogenesis and progression of human osteoarthritis

The cause of osteoarthritis (OA), the most common form of arthritis, is most likely multifactorial. No drug exists to slow the progression or reverse OA disease progression. Ample data support a key role of calcium-containing crystals, such as hydroxyapatite, in OA pathogenesis. The presence of these crystals, far higher in OA than in any other form of arthritis, correlates with the degree of radiographic degeneration. Calcium-containing crystals have potent biologic effects in vitro that emphasize their pathogenic potential. OA-associated matrix and chondrocyte alterations play an intimate role in the crystal deposition process. A major difficulty has been the lack of a simple technique for crystal identification in affected joints. Enhanced effort is needed to establish calcium-containing crystals as a therapeutic target in OA, as current data suggest an intimate association in its pathogenesis and progression.

Calcium crystal deposition and osteoarthritis

Calcium crystals are common and under-recognized participants in osteoarthritis. Excellent evidence supports two hypotheses explaining the relationship between calcium crystal deposition and osteoarthritis. There is ample support for the theory that calcium crystals cause or worsen osteoarthritis and equally compelling evidence to support the theory that osteoarthritis causes or worsens calcium crystal formation. Further research in this area will improve understanding of the pathogenesis of these conditions and should lead to the development of effective therapy for all types of degenerative arthritis.

Lack of association between chondrocalcinosis and increased risk of cartilage loss in knees with osteoarthritis: Results of two prospective longitudinal magnetic resonance imaging studies

OBJECTIVE

To evaluate the relationship between chondrocalcinosis and the progression of knee osteoarthritis (OA) using longitudinal magnetic resonance imaging (MRI) assessments.

METHODS

Longitudinal knee MRIs were obtained in the Boston OA Knee Study (BOKS) and in the Health, Aging and Body Composition (Health ABC) Study. Chondrocalcinosis was determined as present or absent on baseline knee radiographs. Cartilage morphology was graded on paired longitudinal MRIs using the Whole-Organ Magnetic Resonance Imaging Score in 5 cartilage subregions of each of the medial and lateral tibiofemoral joints. Cartilage loss in a subregion was defined as an increase in the cartilage score of > or = 1 (0-4 scale). The risk for change in the number of subregions with cartilage loss was assessed using Poisson regression, with generalized estimating equations to account for correlations. Analyses were adjusted for age, sex, body mass index, baseline cartilage score, and presence of damaged menisci.

RESULTS

In BOKS, 23 of the 265 included knees (9%) had chondrocalcinosis. In Health ABC, 373 knees were included, of which 69 knees (18.5%) had chondrocalcinosis. In BOKS, knees with chondrocalcinosis had a lower risk of cartilage loss compared with knees without chondrocalcinosis (adjusted risk ratio [RR] 0.4, 95% confidence interval [95% CI] 0.2-0.7) (P = 0.002), and there was no difference in risk in Health ABC (adjusted RR 0.9, 95% CI 0.6-1.5) (P = 0.7). Stratification by intact versus damaged menisci produced similar results within each cohort.

CONCLUSION

In knees with OA, the presence of chondrocalcinosis was not associated with increased cartilage loss. These findings do not support the hypothesis that chondrocalcinosis worsens OA progression.

Calcium-containing crystals and osteoarthritis: implications for the clinician

The clinical implication of articular deposits of calcium-containing crystals (specifically of calcium pyrophosphate dihydrate and hydroxyapatite) in osteoarthritis is unknown. Recent longitudinal studies have suggested that in some instances calcium crystals are direct participants in cartilage damage, while in other situations they are merely markers of joint damage. Better understanding of the mechanisms of crystal formation, especially in relation to inorganic pyrophosphate regulation, has lead to potential avenues for therapeutic intervention. The current treatment of osteoarthritis associated with calcium-containing crystals should involve nonsteroidal anti-inflammatory drugs, intra-articular steroids, and in resistant cases, joint irrigation can be considered. While preliminary studies suggest the possibility of favorable benefits from colchicine and hydroxycholorquine in this osteoarthritis disease subset, more rigorous studies need to be conducted to establish their roles.

Apoptosis and the loss of chondrocyte survival signals contribute to articular cartilage degradation in osteoarthritis

Apoptotic death of articular chondrocytes has been implicated in the pathogenesis of osteoarthritis (OA). Apoptotic pathways in chondrocytes are multi-faceted, although some cascades appear to play a greater in vivo role than others. Various catabolic processes are linked to apoptosis in OA cartilage, contributing to the reduction in cartilage integrity. Recent studies suggest that beta1-integrin mediated cell-matrix interactions provide survival signals for chondrocytes. The loss of such interactions and the inability to respond to IGF-1 stimulation may be partly responsible for the hypocellularity and matrix degradation that characterises OA. Here we have reviewed the literature in this area of cartilage cell biology in an effort to consolidate the existing information into a plausible hypothesis regarding the involvement of apoptosis in the pathogenesis of OA. Understanding of the interactions that promote chondrocyte apoptosis and cartilage hypocellularity is essential for developing appropriately targeted therapies for inhibition of chondrocyte apoptosis and the treatment of OA.

Role of S100A8 and S100A9 in neutrophil recruitment in response to monosodium urate monohydrate crystals in the air-pouch model of acute gouty arthritis

OBJECTIVE

To examine the role of chemokines, S100A8, and S100A9 in neutrophil accumulation induced by the causative agent of gout, monosodium urate monohydrate (MSU) crystals.

METHODS

MSU crystal-induced neutrophil migration was studied in the murine air-pouch model. Release of chemokines, S100A8, S100A9, and S100A8/A9 in response to MSU crystals was quantified by enzyme-linked immunosorbent assays. Recruited cells were counted following acetic blue staining, and the subpopulations were characterized by Wright-Giemsa staining of cytospins.

RESULTS

MSU crystals induced the accumulation of neutrophils following injection in the air pouch, which correlated with the release of the chemokines CXCL1, CXCL2, CCL2, and CCL3. However, none of these was found to play an important role in neutrophil migration induced by MSU crystals by passive immunization with antibodies directed against each chemokine. S100A8, S100A9, and S100A8/A9 were also found at high levels in the pouch exudates following injection of MSU crystals. In addition, injection of S100A8, S100A9, or S100A8/A9 led to the accumulation of neutrophils in the murine air pouch, demonstrating their proinflammatory activities in vivo. Passive immunization with anti-S100A8 and anti-S100A9 led to a total inhibition of the accumulation of neutrophils. Finally, S100A8/A9 was found at high concentrations in the synovial fluid of patients with gout.

CONCLUSION

S100A8 and S100A8/A9 are essential to neutrophil migration induced by MSU crystals. These results suggest that they might be involved in the pathogenesis of gout.

Calcium crystals in osteoarthritis

Osteoarthritis is the most common form of arthritis in adults and its incidence increases with age. More than 50% of people aged 65 and older have radiographic changes of knee osteoarthritis. Calcium crystals, including calcium pyrophosphate dihydrate and basic calcium phosphate crystals, are also common in the elderly. Not surprisingly, osteoarthritis and crystal arthropathy frequently coexist. The question of a role for calcium crystals in causing or worsening osteoarthritis has been pondered for many years. Progress in understanding the interrelationships between calcium crystals and osteoarthritis has been slowed by our limited knowledge of the pathogenesis of both osteoarthritis and calcium crystal-induced arthritis and our limited ability to accurately detect calcium crystals. Nonetheless, there are good data from clinical and laboratory studies supporting an important role for calcium crystals in osteoarthritis.

Crystal deposition and osteoarthritis

Calcium-containing crystals are commonly found in osteoarthritic (OA) joints. Although most often found in advanced OA, some calcium pyrophosphate dihydrate and apatite can be present in early stages. These crystals could be factors in pathogenesis of OA and even more likely in the progression of disease. Calcium pyrophosphate dihydrate apatites and other calcium phosphates can be mitogenic, can stimulate the release of metalloproteases, and might have mechanical abrasive effects.

What is the relation between crystals and osteoarthritis?

The nature of the relation between osteoarthritis and the various forms of calcium crystals that are found within osteoarthritic joints continues to challenge and confound researchers. The most basic question is whether such crystals are directly relevant to the development of osteoarthritis, or are merely a byproduct or marker of the disease itself. The past year has produced several studies that elucidate important aspects of the molecular and cellular mechanisms of calcium pyrophosphate dihydrate and apatite crystal formation. Such studies may yield novel targets for therapeutic intervention in crystal-associated osteoarthritis. Other recent studies have provided further understanding of the mechanisms by which crystals induce inflammation. Arthroscopic assessment of patients with knee osteoarthritis refractory to traditional therapy suggests that the combined absence of chondrocalcinosis on plain films and identifiable crystals on compensated polarized light microscopy of synovial fluid from arthrocentesis may not be adequate to exclude clinically relevant crystalline deposition and inflammation. Clinical criteria are needed to identify patients with occult crystalline disease who, by virtue of crystal-induced inflammation, require more aggressive anti-inflammatory therapy than those with noninflammatory osteoarthritis.

The murine homolog of the interleukin-8 receptor CXCR-2 is essential for the occurrence of neutrophilic inflammation in the air pouch model of acute urate crystal-induced gouty synovitis

OBJECTIVE

Acute neutrophil-dependent inflammation is central to acute gout. Urate crystals induce different classes of neutrophil chemotaxins, including certain chemokines (e.g., interleukin-8 [IL-8], growth-related oncogene alpha [GROalpha]) that share CXCR-2 as a receptor. This study was undertaken to assess the role of CXCR-2 ligands in a model of acute gout.

METHODS

Urate crystals were injected into subcutaneous air pouches in mice that expressed or lacked the murine CXCR-2 homolog (mIL-8RH), and the development of neutrophilic inflammation was assessed.

RESULTS

In normal mice, urate crystals induced a 10-fold increase (P < 0.01) in pouch fluid leukocytes (principally neutrophils) at 4 hours. Leukocytes adhered to the pouch lining, where crystals, the mIL-8RH ligand KC/GROalpha, and cells bearing mIL-8RH were abundant. In mIL-8RH(-/-) mice, urate crystals induced a proteinaceous leukocyte-poor exudate at 4 hours, despite crystal-induced activation of resident cells (documented by KC/GROalpha expression).

CONCLUSION

Chemokines that bind the IL-8 receptor CXCR-2 are essential for the development of acute neutrophilic inflammation in response to urate crystals in the subcutaneous air pouch model.

Periodontoid calcium pyrophosphate dihydrate deposition disease: "pseudogout" mass lesions of the craniocervical junction

Between 1984 and 1996, seven patients with symptomatic masses located posterior to the odontoid process and containing calcium pyrophosphate dihydrate crystals were evaluated by the senior author (A.H.M). All patients presented with distal paresthesias and myelopathy and underwent transoral-transpharyngeal resection of the anterior arch of C-I, the odontoid process, and the compressing mass. Histological examination revealed the characteristic changes of calcium pyrophosphate dihydrate (CPPD) deposition disease, with nodular deposits of birefringent rhomboid crystals. On magnetic resonance imaging, the masses appeared predominantly isointense with neural tissue on T1-weighted images and iso-to hyperintense on T2-weighted images. On computerized tomography scans, small area of calcifications within the masses were apparent in all cases. All patients improved postoperatively, with six of seven patients requiring posterior fixation for instability as a second procedure. Calcium pyrophosphate dihydrate deposition causing periodontoid mass lesions is a distinct clinical disease entity that probably is underdiagnosed. In the authors' l opinion, the diagnosis can often be established preoperatively by the distinctive neuroradiological appearance of the masses. Therefore, CPPD deposition disease should be considered in the differential diagnosis of masses of the craniocervical junction, because it is amenable to early surgical intervention. The consulting neuropathologist should be made aware of this diagnostic possibility at the time of surgery.