Effect of synthetic calcium pyrophosphate and hydroxyapatite crystals on the interaction of human blood mononuclear cells with chondrocytes, synovial cells, and fibroblasts

The role of Interleukin-1 receptor antagonist as a treatment option in calcium pyrophosphate crystal deposition disease

Calcium Pyrophosphate Crystal Deposition (CPPD) disease is characterized by the deposition of calcium pyrophosphate crystals in the cartilage. In most cases, it can manifest as a subclinical condition named chondrocalcinosis, often revealed by joint x-ray examination. In other cases, deposition can cause flares of arthritis, known as acute CPP crystal arthritis. In the last few years, many pathogenic pathways have been discovered. Interleukin-1 (IL-1) plays a key role in the pathogenesis of CPPD disease, both as a mediator of inflammatory response to crystals and as a promoter of damage to articular cartilage. In this review, we investigated the role of IL-1R inhibitor, such as Anakinra, as an alternative to the various therapeutic strategies for CPPD disease, especially among patients resistant to traditional treatment with NSAIDs, corticosteroids and colchicine.

Update on colchicine, 2017

Colchicine is an ancient medication that is currently approved for the treatment of gout and FMF. However, colchicine has a wide range of anti-inflammatory activities, and studies indicate that it may be beneficial in a variety of other conditions. This paper reviews the evidence for the well-established use of colchicine in gout, as well as several other rheumatic diseases. In addition, we highlight the potential benefit of colchicine in cardiac disease, including coronary artery disease in patients both with and without gout.

Calcific tendonitis of the rotator cuff: From formation to resorption

Calcific tendonitis of the rotator cuff is due to apatite deposits in the shoulder tendons. Patients affected by calcific tendonitis have chronic shoulder pain and disability. Although the disease is frequent, about 10 to 42% of painful shoulders, mechanisms leading to this pathological mineralization are still largely unknown. Research reported in the 1990s suggested that the formation of calcific deposits is linked to cells looking like chondrocytes identified around calcium deposits within a fibrocartilage area. They were considered to be derived from tenocytes but more recently, tendon stem cells, able to differentiate into chondrocytes, were isolated. The pro-mineralizing properties of these chondrocytes-like cells, especially the role of alkaline phosphatase, are not currently clarified. The calcium deposits contain poorly crystalline carbonated apatite associated with protein. Among these proteins, only osteopontin has been consistently identified as a potential regulating factor. During the disease, spontaneous resorption can occur with migration of apatite crystals into the subacromial bursa causing severe pain and restriction of movement. In in vivo and in vitro experiments, apatite crystals were able to induce an influx of leucocytes and a release of IL-1β and IL-18 through the activation of the NLRP3 inflammasome. However, mechanisms leading to spontaneous resolution of this inflammation and disappearance of the calcification still need to be elucidated.

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.

How can calcium pyrophosphate crystals induce inflammation in hypophosphatasia or chronic inflammatory joint diseases?

Hypophosphatasia (HP) is a rare inborn error of bone and mineral metabolism characterized by a defect in the tissue non-specific alkaline phosphatase (TNSALP) gene. Calcium pyrophosphate dihydrate (CPPD) crystals are known to accumulate as substrates of TNSALP in tissues and joints of patients with HP. In CPPD-induced arthritis these crystals are known to induce an inflammatory response. HP patients do suffer from pain in their lower extremities. However, it is not clear whether CPPD crystals contribute to these musculoskeletal complaints in HP. As long as there is no curative treatment of HP, symptomatic treatment in order to improve clinical features, especially with regard to pain and physical activity, is of major interest to the patients. Knowledge of the mechanisms underlying crystal-induced cell activation, however, is limited. Here we describe recent advances in elucidating the signal transduction pathways activated by CPPD crystals as endogenous "danger signals". Recent investigations provided evidence that Toll/interleukin-1 receptor (TIR) domain containing receptors including Toll-like receptors (TLRs) and interleukin-1 receptor (IL-1R), as well as the triggering receptor expressed on myeloid cells 1 (TREM-1) and the NACHT-leucin rich repeat and pyrin-domain-containing protein (NALP3) containing inflammasome are essentially involved in acute CPPD crystal-induced inflammation. These receptors are considered in part as components of the innate immune system. Further studies are needed to improve our understanding of the pathophysiological mechanisms leading to inflammation and tissue destruction associated with deposition of microcrystals. They might support the development of new therapeutic strategies for crystal-induced inflammation. Eventually, patients with HP might as well profit from such strategies addressing these metabolic disorders secondary to the gene defect.

Long-term follow-up of bone mineral density in childhood hypophosphatasia

OBJECTIVE

Hypophosphatasia (HP; MIM 241510) is an inborn error of bone metabolism, characterized by a genetic defect in the gene of the tissue-non-specific alkaline phosphatase TNSALP. Long-term data on bone mineral density measurements are not available.

METHODS

We have analyzed changes of bone mineral density (pQCT and DXA) prospectively during 4years of follow-up in a cohort of 6 patients with childhood HP.

RESULTS

At diagnosis hypermineralization of the trabecular bone in the metaphyseal area of long bones in affected children was noted. During 4 years of follow-up a gradual, significant decrease of mineralization was noted in the radial metaphyses. In contrast, BMC by DXA and total body DXA values were stable in comparison to healthy controls. During follow-up a systemic hyperprostaglandinism was documented in the majority of the patients. Non-steroidal anti-inflammatory drug treatment was evaluated by measuring prostaglandin excretion in the urine.

CONCLUSIONS

Metaphyseal hypermineralization in childhood HP, which might be a compensation for a mechanically incompetent bony structure, decreased over time. There might be a pathophysiological link to continually elevated systemic prostaglandins.

Calcium crystal deposition diseases: update on pathogenesis and manifestations

Basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate crystals are the most common types of pathologic calcium-containing crystals. Although these crystals long have been associated with a variety of rheumatic syndromes, recent evidence implicates BCP crystals in the pathogenesis of breast cancer and atherosclerosis. Although understanding of molecular mechanisms involved in generating these pathologic effects has been advanced significantly in recent years, they still are understood incompletely. Such advances are essential to the ongoing search for effective therapies for crystal-associated diseases.

Effect of Interleukin-1β on Transforming Growth Factor-Beta and Bone Morphogenetic Protein-2 Expression in Human Periodontal Ligament and Alveolar Bone Cells in Culture: Modulation by Avocado and Soybean Unsaponifiables

BACKGROUND

In periodontal disease, interleukin-1beta (IL-1beta) is responsible for the matrix breakdown through excessive production of degrading enzymes by periodontal ligament fibroblasts and osteoblasts. Transforming growth factor-beta (TGF-beta) plays an important role in tissue regeneration as one of the factors capable of counteracting IL-1beta effects. In this study, we investigated the in vitro effect of avocado and soya unsaponifiables (ASU) on the expression of TGF-beta1, TGF-beta2, and bone morphogenetic protein-2 (BMP-2) by human periodontal ligament (HPL) and human alveolar bone (HAB) cells in the presence of IL-1beta.

METHODS

HPL and HAB cells were incubated for 48 hours with ASU (10 microg/ml) in the presence or absence of IL-1beta (10 ng/ml). The steady-state levels of TGF-beta1, TGF-beta2, and BMP-2 mRNAs were determined by Northern blot or reverse transcription-polymerase chain reaction (RT-PCR). The amounts of TGF-beta1 and TGF-beta2 proteins were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The data indicated that IL-1beta strongly decreases the expression of TGF-beta1 and TGF-beta2 by HPL cells. ASU were capable of opposing the cytokine effect. In HAB cells, TGF-beta1 and BMP-2 mRNA levels were downregulated by the cytokine. ASU were found to reverse the IL-1beta-inhibiting effect. In contrast, the cytokine stimulated the production of TGF-beta2 in alveolar bone cells, with no significant effect of ASU.

CONCLUSIONS

The results indicate that the IL-1beta-driven erosive effect in periodontitis could be enhanced by a decreased expression of members of the TGF-beta family. The ASU stimulation of TGF-beta1, TGF-beta2, and BMP-2 expression may explain their promoting effects in the treatment of periodontal disorders, at least partly. These findings support the hypothesis that ASU could exert a preventive action on the deleterious effects exerted by IL-1beta in periodontal diseases.

Effective NSAID treatment indicates that hyperprostaglandinism is affecting the clinical severity of childhood hypophosphatasia

Background

Hypophosphatasia (HP) is an inborn error of bone metabolism characterized by a genetic defect in the gene encoding the tissue-nonspecific alkaline phosphatase (TNSALP). There is a lack of knowledge as to how the variability and clinical severity of the HP phenotype (especially pain and walking impairment) are related to metabolic disturbances or impairments, subsequent to the molecular defect.

Methods

We analyzed the changes in clinical symptoms and the prostaglandin (PG) metabolism in response to treatment with non-steroidal anti-inflammatory drugs (NSAIDs) in six children affected by childhood HP. In addition, by exposing HP fibroblasts to pyridoxal phosphate and/or calcium pyrophosphate in vitro, we analyzed whether the alterations in PG levels are sequelae related to the metabolic defect.

Results

Childhood HP patients, who often complain about pain in the lower limbs without evident fractures, have systemic hyperprostaglandinism. Symptomatic anti-inflammatory treatment with NSAIDs significantly improved pain-associated physical impairment. Calcium pyrophosphate, but not pyridoxal phosphate, induced cyclooxygenase-2 (COX-2) gene expression and PG production in HP and normal fibroblasts in vitro.

Conclusion

Clinical features of childhood HP related to pain in the lower legs may be, at least in part, sequelae related to elevated PG levels, secondary to the primary metabolic defect. Consequently, NSAID treatment does improve the clinical features of childhood HP.

Octacalcium phosphate crystals directly stimulate expression of inducible nitric oxide synthase through p38 and JNK mitogen-activated protein kinases in articular chondrocytes

Basic calcium phosphate (BCP) crystals, including hydroxyapatite, octacalcium phosphate (OCP) and carbonate-apatite, have been associated with severe osteoarthritis and several degenerative arthropathies. Most studies have considered the chondrocyte to be a bystander in the pathogenesis of calcium crystal deposition disease, assuming that synovial cell cytokines were the only triggers of chondrocyte activation. In the present study we identified direct activation of articular chondrocytes by OCP crystals, which are the BCP crystals with the greatest potential for inducing inflammation. OCP crystals induced nitric oxide (NO) production and inducible nitric oxide synthase (NOS) mRNA expression by isolated articular chondrocytes and cartilage fragments, in a dose-dependent manner and with variations over time. OCP crystals also induced IL-1β mRNA expression. Using pharmacological and cytokine inhibitors, we observed that OCP crystals induced NO production and inducible NOS mRNA activation were regulated at both the transcriptional and the translational levels; were independent from IL-1β gene activation; and involved p38 and c-Jun amino-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) pathways, as further confirmed by OCP crystal-induced p38 and JNK MAPK phosphorylation. Taken together, our data suggest that the transcriptional inducible NOS response to OCP crystals involved both the p38 and the JNK MAPK pathways, probably under the control of activator protein-1. NO, a major mediator of cartilage degradation, can be directly produced by BCP crystals in chondrocytes. Together with synovial activation, this direct mechanism may be important in the pathogenesis of destructive arthropathies triggered by microcrystals.

Biologic effects of calcium-containing crystals

PURPOSE OF REVIEW

Calcium-containing crystals can cause the degeneration of articular tissues in two separate pathways. In the direct pathway, crystals directly induce synoviocytes to proliferate and produce metalloproteinases and prostaglandins. The other pathway, the paracrine pathway, involves the interaction between crystals and macrophages/monocytes, which leads to the synthesis and release of cytokines, which can reinforce the action of crystals on synoviocytes and/or induce chondrocytes to secrete enzymes and which eventually causes the degeneration of articular tissues. The purpose of this review is to highlight the recent findings of the biologic effect of these crystals.

RECENT FINDINGS

In the past few years, major advances in the understanding of the biologic effect of crystals and the signal transduction pathway of crystal-induced cell activation offer a unique opportunity to examine the role of crystal in osteoarthritis and cartilage degeneration.

SUMMARY

Evidence for a causal role of crystals in cartilage degeneration in osteoarthritis is primarily inferential and is based on correlative data. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Measurements of putative markers of cartilage breakdown suggest that these crystals magnify the degenerative process. Studies have shown two potential mechanisms by which crystals cause degeneration. These involve the stimulation of mitogenesis in synovial fibroblasts and the secretion of metalloproteinases by cells that subject these crystals to phagocytosis. New information on how crystals form and how they exert their biologic effects will help in the design of an effective therapeutic approach.

Hydroxyapatite deposition disease of the joint

Basic calcium phosphate (BCP) crystals include partially carbonate-substituted hydroxyapatite, octacalcium phosphate, and tricalcium phosphate. They may form deposits, which are frequently asymptomatic but may give rise to a number of clinical syndromes including calcific periarthritis, Milwaukee shoulder syndrome, and osteoarthritis, in and around joints. Recent data suggest that magnesium whitlockite, another form of BCP, may play a pathologic role in arthritis. Data from the past year have provided further understanding of the mechanisms by which BCP crystals induce inflammation and degeneration. There remains no specific treatment to modify the effects of BCP crystals. Although potential drugs are being identified as the complex pathophysiology of BCP crystals is unraveled, much work remains to be done in order to translate research advances to date into tangible clinical benefits.

Milwaukee shoulder: correlating possible etiologic variables

The current study evaluated the relative correlation of apatite crystal-induced inflammation and rotator cuff deficiency in the development of cuff tear arthropathy. Thirty-seven patients with full thickness rotator cuff tears were evaluated by history, physical examination, and plain radiographs. Thirty patients had surgical intervention for their rotator cuff defects, and calipers were used intraoperatively to quantify the size of the tear in its largest diameter. The remaining seven patients were treated nonoperatively and the size of the tear was quantified using magnetic resonance imaging. Synovial fluid was obtained from all patients and analyzed for crystal content using an alizarin red stain. Synovial fluid also was analyzed for leukocyte count and differential, prostaglandin E, and matrix metalloproteinase. An unpaired Student's t test revealed that significantly higher levels of prostaglandin E were found in the synovial fluid of patients with apatite crystals, shown by alizarin red stain. Chi squared analysis showed that patients with elevated crystal levels were significantly more likely to have large rotator cuff tears or glenohumeral arthritis. Establishing such relations potentially can elucidate the etiology and treatment of this complex disorder.(2) (2)

The role of crystals in articular tissue degeneration

The deposition of calcium-containing crystals in articular tissues is probably an underrecognized event. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Perhaps the most compelling argument favoring a role for crystals in causing osteoarthritis stems from their in vitro effects on articular tissues. In this short review, we will discuss the fact that crystals can cause the degeneration of articular tissues in 2 separate pathways. In the "Direct" pathway, crystals directly induce fibroblast-like synoviocytes to proliferate and produce metalloproteinases and prostaglandins. The other "Paracrine pathway" involves the interaction between crystals and macrophages/monocytes, which leads to synthesis and release of cytokines that can reinforce the action of crystals on synoviocytes and induce chondrocytes to secrete enzymes, eventually causing the degeneration of articular tissues.

Treatment of childhood hypophosphatasia with nonsteroidal antiinflammatory drugs

Hypophosphatasia (HP) is an inborn error of metabolism that is characterized by reduced bone mineralization. The aim of this investigation was to evaluate treatment of incapacitating lower limb pain in patients with childhood HP using nonsteroidal antiinflammatory drugs (NSAID). All patients (seven boys; age 32 months to 16 years) presented with delayed walking, the typical waddling gait, muscular weakness of the lower limbs, and a limited walking distance. Six patients had severe diffuse lower limb pain following physical activity and were therefore treated with NSAID. The benefit of this treatment was evaluated clinically and by measurement of renally (PGE2) and systemically (PGE-M) derived prostaglandins (PG) in urine before and during therapy. After treatment with NSAID all six patients showed marked clinical improvement with reduced pain, increased muscle strength, and a normalized walking distance. Levels of PGE-M, which had been elevated in four patients prior to therapy, returned to normal. The use of NSAID in childhood HP should be considered as a possible therapeutic approach because the quality of life in these patients is markedly impaired by pain of the limbs. Elevated PG might play a role in the bone metabolism of HP patients.

Bone metabolism and bone mineral density in childhood hypophosphatasia

Childhood hypophosphatasia (HP) is an inborn error of bone metabolism, characterized by a reduced tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). Bone mineral density (BMD) in childhood HP has not been reported so far. We measured BMD, in addition to markers of bone metabolism, in 6 boys with childhood HP (age 2-13 years) and in 10 parents and one sibling, each carrying the autosomal-recessive trait. BMD, measured by peripheral quantitative computed tomography (pQCT) and by dual-energy X-ray absorptiometry (DXA), was expressed as standard deviation from the normal mean (Z scores) and compared with bone mineralization by standard X-rays of the same locations. HP was confirmed by low TNSALP and its elevated substrates. In patients, BMD of the total body or spine, measured by DXA, was in the lower normal range. Total BMD of the distal metaphyses of the radius, measured by pQCT, was normal (Z score: mean +1.5). However, trabecular BMD of both radius (Z score: mean +4) and femur was grossly elevated. In parallel, X-rays showed reduced transradiancy of the radial and femoral metaphyses in all patients. In parents of patients with HP, BMD was in the lower normal range. Only one father had a decreased lumbar BMD. The discrepancy in BMD between cortical and trabecular bone of the metaphyses in patients was not present in their relatives. TNSALP levels in all first degree relatives were just below or in the lower normal range. The markers of bone turnover hydroxyproline and free deoxypyridinoline in urine were normal in patients and relatives. Hypermineralization/sclerosis of trabecular bone might serve as a compensation for a mechanically incompetent bony structure due to an impaired mineralization of cartilage caused by the genetic deficiency of alkaline phosphatase.

Basic calcium phosphate crystal induction of collagenase 1 and stromelysin expression is dependent on a p42/44 mitogen-activated protein kinase signal transduction pathway

Synovial fluid basic calcium phosphate (BCP) crystals are markers of severe joint degeneration in osteoarthritis. These crystals are mitogenic and induce protooncogene expression and matrix metalloproteinase (MMP) synthesis and secretion in human fibroblasts, effects that are specifically blocked by phosphocitrate (PC). We have recently determined that crystals transduce signals to the nucleus via the activation of the p42 and p44 mitogen-activated protein (MAP) kinases (Nair et al., 1997, J Biol Chem 272:18920-18925). Treatment of human fibroblasts (HF) with BCP induces phosphorylation of p42/44 MAPK, which is inhibited by PC in a dose-dependent manner. Blocking of p42/44 MAPK signal transduction with an inhibitor (PD98059) of MEK1, an upstream activator of MAPKs, reduces crystal-induced p42/44 MAPK activation and significantly inhibits crystal-induced cell proliferation. Based on these findings, we sought to determine the role of the p42/44 MAPK signal transduction pathway in crystal-induced expression of matrix MMPs. We demonstrate suppression of crystal-induced MMPs via the utilization of two different MEK inhibitors: PD98059 and the recently described U0126, a novel inhibitor of MEK1 and MEK2. Treatment of HF with PD98059 blocks the induction of crystal-stimulated collagenase 1 (MMP-1) and stromelysin (MMP-3) expression. PD98059 and PC reduced the level of crystal-induced MMP-1 and MMP-3 mRNA expression to that observed in nonstimulated cells. Likewise, PD98059 treatment of HF blocked the epidermal growth factor (EGF)- and crystal-induced increases in MMP-1 and MMP-3 protein expression and secretion as demonstrated by Western blotting and zymography. Treatment of HF with U0126 inhibits EGF-induced phosphorylation of p42/44 MAPK as well as crystal- and EGF-induced upregulation of MMP-1 mRNA. Additionally, we demonstrate that treatment of HF with BCP, EGF, or PD98059 does not significantly alter levels of gelatinase A (MMP-2) mRNA and protein expression.

Monosodium Urate Microcrystals Induce Cyclooxygenase-2 in Human Monocytes

The formation and deposition of monosodium urate (MSU) microcrystals in articular and periarticular tissues is the causative agent of acute or chronic inflammatory responses known as gouty arthritis. Mononuclear phagocyte activation is involved in early triggering events of gout attacks. Because stimulated mononuclear phagocytes can constitute an important source of the inducible isoform of cyclooxygenase (COX-2), we evaluated the effects that proinflammatory microcrystals might have on COX-2 protein expression in crystal-stimulated monocytes. We found that MSU crystals, but not calcium pyrophosphate dihydrate (CPPD) crystals, induced COX-2, which correlated with the synthesis of prostaglandin E2 (PGE2) and thromboxane A2(TXA2). Crystal-induced de novo synthesis of COX-2 was dependent on transcriptional and translational events. Inhibition of tyrosine phosphorylation, by herbimycin A, blocked crystal-induced COX-2. Similarly, an inhibitor of the p38 mitogen-activated protein kinase, SB 203580, inhibited the stimulation of COX-2. Colchicine inhibited crystal-induced COX-2. In all cases, prostanoid synthesis was concomitantly inhibited. Taken together, these results implicate COX-2 in the development of MSU-induced inflammation.

Monosodium Urate Microcrystals Induce Cyclooxygenase-2 in Human Monocytes

The formation and deposition of monosodium urate (MSU) microcrystals in articular and periarticular tissues is the causative agent of acute or chronic inflammatory responses known as gouty arthritis. Mononuclear phagocyte activation is involved in early triggering events of gout attacks. Because stimulated mononuclear phagocytes can constitute an important source of the inducible isoform of cyclooxygenase (COX-2), we evaluated the effects that proinflammatory microcrystals might have on COX-2 protein expression in crystal-stimulated monocytes. We found that MSU crystals, but not calcium pyrophosphate dihydrate (CPPD) crystals, induced COX-2, which correlated with the synthesis of prostaglandin E2 (PGE2) and thromboxane A2(TXA2). Crystal-induced de novo synthesis of COX-2 was dependent on transcriptional and translational events. Inhibition of tyrosine phosphorylation, by herbimycin A, blocked crystal-induced COX-2. Similarly, an inhibitor of the p38 mitogen-activated protein kinase, SB 203580, inhibited the stimulation of COX-2. Colchicine inhibited crystal-induced COX-2. In all cases, prostanoid synthesis was concomitantly inhibited. Taken together, these results implicate COX-2 in the development of MSU-induced inflammation.

Phosphocitrate inhibits a basic calcium phosphate and calcium pyrophosphate dihydrate crystal-induced mitogen-activated protein kinase cascade signal transduction pathway

Calcium deposition diseases caused by calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals are a significant source of morbidity in the elderly. We have shown previously that both types of crystals can induce mitogenesis, as well as metalloproteinase synthesis and secretion by fibroblasts and chondrocytes. These responses may promote degradation of articular tissues. We have also shown previously that both CPPD and BCP crystals activate expression of the c-fos and c-jun proto-oncogenes. Phosphocitrate (PC) can specifically block mitogenesis and proto-oncogene expression induced by either BCP or CPPD crystals in 3T3 cells and human fibroblasts, suggesting that PC may be an effective therapy for calcium deposition diseases. To understand how PC inhibits BCP and CPPD-mediated cellular effects, we have investigated the mechanism by which BCP and CPPD transduce signals to the nucleus. Here we demonstrate that BCP and CPPD crystals activate a protein kinase signal transduction pathway involving p42 and p44 mitogen-activated protein (MAP) kinases (ERK 2 and ERK 1). BCP and CPPD also cause phosphorylation of a nuclear transcription factor, cyclic AMP response element-binding protein (CREB), on serine 133, a residue essential for CREB's ability to transactivate. Treatment of cells with PC at concentrations of 10(-3) to 10(-5) M blocked both the activation of p42/p44 MAP kinases, and CREB serine 133 phosphorylation, in a dose-dependent fashion. At 10(-3) M, a PC analogue, n-sulfo-2-aminotricarballylate and citrate also modulate this signal transduction pathway. Inhibition by PC is specific for BCP- and CPPD-mediated signaling, since all three compounds had no effect on serum-induced p42/P44 or interleukin-1beta induced p38 MAP kinase activities. Treatment of cells with an inhibitor of MEK1, an upstream activator of MAPKs, significantly inhibited crystal-induced cell proliferation, suggesting that the MAPK pathway is a significant mediator of crystal-induced signals.

Calcium phosphate particle induction of metalloproteinase and mitogenesis: effect of particle sizes

Calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals [hydroxyapatite (HA), octacalcium phosphate, tricalcium phosphate] are common in osteoarthritis knee effusions, and are often associated with low-grade synovial proliferation and inflammation. Calcium-containing crystals including HA, are known to have a number of biologic effects on culture cells such induction of mitogenesis, stimulation of Prostaglandin E2 (PGE2) production via the phospholipase A2/cyclo-oxygenase pathway, activation of phospholipase C and inositol phospholipid hydrolysis, induction of metalloproteinase synthesis and induction of proto-oncogenes (c-fos and c-myc). While endocytosis of HA particles is prerequisite of the mitogenic effect of calcium-containing crystals in fibroblasts, it is not known whether endocytosis is required for crystal-induced metalloproteinase synthesis. In the present series of experiments, we examine the effect of three different sizes (106, 46, and 17 microns mean diameters) well-characterized spherical HA particles on the induction of mitogenesis and metalloproteinase synthesis on human fibroblasts. We showed that endocytosis is required for HA particles to induce synthesis of metalloproteinases.

Specific inhibition of basic calcium phosphate and calcium pyrophosphate crystal-induction of metalloproteinase synthesis by phosphocitrate

Calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystal deposition diseases are a group of heterogeneous arthritides which are a significant source of morbidity in the elderly. Both crystals induced mitogenesis and metalloproteinase (MP) synthesis and secretion by fibroblasts and chondrocytes which may promote degradation of intra-articular tissue. We have previously shown that phosphocitrate (PC), an inhibitor of hydroxyapatite crystallization, specifically blocks BCP crystal-induced mitogenesis in 3T3 cells. This led us to examine the effect of PC on BCP and CPPD crystal induction of MP synthesis in human fibroblasts. PC (10(-3) to 10(-4) M) specifically inhibited the crystal-induced collagenase and stromelysin mRNA accumulation while having no effect on epidermal growth factor-induced or basal levels of mRNA for both enzymes. Western blots (collagenase) of conditioned media confirmed that PC blocked crystal-induced proteinase secretion as well. Moreover, PC (10(-3) M) also blocked the crystal induction of c-fos and c-jun. Since FOS and JUN proteins form a transacting activator (AP-1) for expression of collagenase and stromelysin genes, PC may block the synthesis of both enzymes by inhibiting the transcription of c-fos and c-jun.

Acceleration of experimental lapine osteoarthritis by calcium pyrophosphate microcrystalline synovitis

OBJECTIVE

To investigate the effects of chronic calcium pyrophosphate dihydrate (CPPD) synovitis on the development of osteoarthritic (OA) lesions in an animal model.

METHODS

OA was induced in the right knees of 30 male New Zealand white rabbits by partial lateral meniscectomy and section of the fibular collateral and sesamoid ligaments (PLM/LS), followed by 8 weekly intraarticular (IA) injections of 1 mg (low-dose) or 10 mg (high-dose) of CPPD crystals in 3 sets of experiments (10 rabbits each). The contralateral left knees served as controls: experiment 1 PLM/LS alone, experiment 2 8 weekly IA injections of CPPD crystals alone, and experiment 3 sham surgery plus 8 weekly IA injections of CPPD crystals.

RESULTS

At 8 weeks, repeated IA injections of low-dose and high-dose CPPD crystals into meniscectomized right knees resulted in more severe OA than in meniscectomized but noninjected left knees (experiment 1) (P = 0.003 and P = 0.001, respectively). One-fourth of the meniscectomized knees (11 of 40), both CPPD-injected and noninjected, showed embedded synovial cartilage shards.

CONCLUSION

The data demonstrate a worsening effect of chronic CPPD crystal-induced synovitis on experimental OA produced in the rabbit knees by PLM/LS, and support a possible role for CPPD microcrystalline inflammation in the progression of OA lesions in clinical CPPD crystal deposition disease.

Crystals in equine articular cartilage

Crystal deposits have been observed in equine articular cartilage and identified by scanning electron microscopy and X-ray diffraction as octacalcium phosphate and calcium pyrophosphate dihydrate. Of 89 equine fetlock joints examined 10 contained evidence of calcification visible by eye. It is suggested that the deposition of crystals may be a mediator of arthritis in horses and may also cause damage directly.

Crystal-neutrophil interactions lead to interleukin-1 synthesis

Normal human blood neutrophils were studied for their capacity to synthesize and release interleukin-1 (IL-1) species after phagocytosis of triclinic monosodium urate (MSU) and calcium pyrophosphate dihydrate crystals (CPPD). MSU crystals were more potent inducers of IL-1 generation than CPPD or unopsonized zymosan. Microcrystal-stimulated neutrophils characteristically secreted most of the newly synthesized IL-1. Colchicine partly inhibited the secretion of IL-1 by neutrophils during phagocytosis of solid particles. However, colchicine selectively inhibited IL-1 synthesis induced by microcrystals. These results suggest that neutrophil-derived IL-1 may contribute to the pathogenesis of crystal-induced arthritis.

Chondroprotective action of salmon calcitonin in experimental arthropathies

To assess whether calcitonin exerts an influence on cartilage, three models of arthropathies in rabbits--representing three different modes of cartilage destruction--were used: (1) corticosteroid administration (endocrinological disturbances model); (2) meniscectomy (mechanical stress model); and (3) immobilization of the hind leg (nutritional disorder model). After 12 weeks of methylprednisolone (MP) administration, the rabbit femur heads displayed cartilage erosions, marked decrease of glycosaminoglycans (GAG) content, and narrowing of joint spaces. Elevation of serum uronic acid, activity of alkaline phosphatase, and calmodulin content was evident. All these changes were minimal--close to normal--in the group treated for 12 weeks with MP + salmon calcitonin (sCT). Partial meniscectomy and hind leg immobilization caused statistically significant loss of GAG from the cartilage and narrowing of the knee joint space during the same experimental period, 12 weeks. In both these models the groups of rabbits treated simultaneously with sCT showed only insignificantly smaller joint spaces and GAG content. These results support our hypothesis of a chondroprotective property of calcitonin. However, the mechanism through which calcitonin influences joint cartilage remains unknown. A direct effect of calcitonin on cultivated chondrocytes, as well as the role of calmodulin, beta-endorphins, calcium, and interleukin-1 in the process are discussed.

Inhibition of basic calcium phosphate crystal-induced mitogenesis by phosphocitrate

Basic calcium phosphate crystals control the traverse of cells from the Go/G1 to S-phase of the cell cycle and initiate proliferation by rendering fibroblasts competent to respond to insulin-like growth factors in plasma. Simultaneous addition of phosphocitrate [a powerful inhibitor of hydroxyapatite crystallization] to cells exposed to basic calcium phosphate crystals caused a dose-dependent inhibition of crystal-induced DNA synthesis and c-fos transcription. This inhibition was specific for crystal-induced mitogenesis, since similar concentrations of phosphocitrate had no effects on either PDGF or 10% calf serum-induced thymidine incorporation and c-fos transcription.

Inflammatory microcrystals stimulate interleukin-6 production and secretion by human monocytes and synoviocytes

Crystal-related joint diseases are often associated with systemic inflammatory manifestations, including increased levels of acute-phase proteins, leukocytosis, and fever. Recently, interleukin-6 (IL-6) has been identified as a pluripotent mediator of inflammatory and immunologic responses and the major hepatocyte-stimulating factor. In this study, we demonstrated that monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals, and to a lesser extent, hydroxyapatite crystals, increased IL-6 production by synoviocytes and monocytes in vitro. Immunoprecipitation experiments showed that MSU and CPPD crystals, but not hydroxyapatite crystals, were able to increase the release of newly synthesized IL-6. Crystal-induced IL-6 stimulated acute-phase protein synthesis, immunoglobulin production, and hybridoma cell proliferation, which was neutralized by a specific antibody to IL-6. High levels of IL-6 were found in synovial fluid from patients with gout and pseudogout. These results demonstrate that MSU and CPPD crystals can induce IL-6 production in synoviocytes and monocytes, and that synovial fluid from patients with gout and pseudogout contains high levels of IL-6. Crystal-induced IL-6 is likely to be an important mediator of inflammatory responses in acute gout and pseudogout.

Synovial fluid hydroxyapatite crystals: detection thresholds of two methods

A method of synovial fluid preparation giving optimal hydroxyapatite detection as well as definitions of the threshold masses of hydroxyapatite in viscous synovial fluid detectable by x ray diffraction and scanning electron microscopy with energy dispersive analysis is reported. Use of an equal volume of 100% hydrazine with the synovial fluid optimised detection of hydroxyapatite. By x ray diffraction the threshold mass of hydroxyapatite was 500 micrograms and by scanning electron microscopy with associated energy dispersive analysis 5 micrograms.

Synovium as a source of interleukin 6 in vitro. Contribution to local and systemic manifestations of arthritis

Synovial inflammation is often associated with systemic changes, such as increased levels of acute phase proteins and hypergammaglobulinemia, which cannot be explained by the cytokines described in synovial fluids and synoviocyte secretions. Interleukin 6 (IL-6) has recently been characterized as a mediator of multiple inflammatory responses. This cytokine promotes T and B lymphocyte growth and differentiation, and acute phase protein synthesis. We therefore examined IL-6 production by human synoviocytes and its presence in synovial fluids. In vitro, synoviocytes spontaneously released IL-6, which was increased by IL-1 and tumor necrosis factor-alpha. Synoviocyte-derived IL-6 activity was able to induce hybridoma-plasmacytoma proliferation, and immunoglobulin and acute-phase protein synthesis. The synovial fluids from patients with diverse arthropathies contained IL-6 activity, but higher levels were present in inflammatory arthropathies than in osteoarthritis. These results demonstrate that synoviocytes are a potent source of IL-6, which can contribute to important manifestations of inflammatory arthropathies.