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A naturally occurring nonsense truncation mutation of the inorganic pyrophosphate (PPi)-generating nucleoside triphosphate pyrophosphohydrolase (NTPPPH) PC-1 is associated with spinal and periarticular ligament hyperostosis and cartilage calcification in "tiptoe walking" (ttw) mice. Thus, we tested the hypothesis that PC-1 acts directly in the extracellular matrix to restrain mineralization. Cultured osteoblastic MC3T3 cells expressed PC-1 mRNA and produced hydroxyapatite deposits at 12-14 days. NTPPPH activity increased steadily over 14 days. Transforming growth factor-beta and 1,25-dihydroxyvitamin D3 increased PC-1 and NTPPPH in matrix vesicles (MVs). Because PC-1/NTPPPH was regulated in mineralizing MC3T3 cells, we stably transfected or infected cells with recombinant adenovirus, in order to express 2- to 6-fold more PC-1. PC-1/NTPPPH and PPi content increased severalfold in MVs derived from cells transfected with PC-1. Furthermore, MC3T3 cells transfected with PC-1 deposited approximately 80-90% less hydroxyapatite (by weight) than cells transfected with empty plasmid or enzymatically inactive PC-1. ATP-dependent 45Ca precipitation by MVs from cells overexpressing active PC-1 was comparably diminished. Thus, regulation of PC-1 controls the PPi content and function of osteoblast-derived MVs and matrix hydroxyapatite deposition. PC-1 may provide a novel therapeutic target in certain disorders of bone mineralization.

The recruitment of mononuclear leukocytes, and the migration, growth and activation of macrophages, lymphocytes and smooth muscle cells within lesions, are critical features of the chronic inflammatory response that typifies atherogenesis. Chemokines are members of a superfamily of small polypeptides that mediate not only migration, but also growth and activation of leukocytes and a variety of other cells. Monocyte chemoattractant and activating protein-1 was the first chemokine to be implicated in leukocyte-mediated inflammation in atherosclerosis. This review emphasizes new information on the potential atherogenic roles of monocyte chemoattractant and activating protein-1 and several other closely related chemokines of the C-C subfamily. We focus particular attention on the newly recognized atherogenic role of a subgroup of closely related chemokines of the C-X-C subfamily that includes interleukin-8 and growth regulated oncogene alpha. We also discuss new studies that reveal how CD40 ligand and certain other stimuli can promote chemokine expression in atherosclerosis.

A fundamental question in endochondral development is why the expression of parathyroid hormone-related protein (PTHrP), which inhibits chondrocyte maturation and mineralization, becomes attenuated at the stage of chondrocyte hypertrophy. To address this question, we used clonal, phenotypically stable SV40-immortalized murine endochondral chondrocytes that express a growth-arrested hypertrophic phenotype in culture (MCT cells). Addition of individual cytokines to the medium of MCT cells revealed that bone morphogenetic protein (BMP)-6, which commits chondrocytes to hypertrophy, markedly inhibited PTHrP production. This activity was shared by three other osteogenic bone morphogenetic proteins (BMP-2, BMP-4, and BMP-7) and by transforming growth factor beta (TGF-beta), which all inhibited the level of PTHrP mRNA. In contrast, basic fibroblast growth factor (bFGF), an inhibitor of chondrocyte maturation to hypertrophy, induced PTHrP in MCT cells and antagonized the effects of BMP-2, BMP-4, BMP-6, and BMP-7 and TGF-beta on PTHrP expression. Opposing effects of bFGF and BMPs also were exerted on the elaboration of inorganic pyrophosphatase (PPi), which regulates the ability of hypertrophic chondrocytes to mineralize the matrix. Specifically, BMP-2 and BMP-4, but not BMP-6 and BMP-7, shared the ability of TGF-beta to induce PPi release, and this activity was inhibited by bFGF in MCT cells. Our results suggest that effects on PTHrP expression could contribute to the ability of BMP-6 to promote chondrocyte maturation. BMPs and bFGF exert opposing effects on more than one function in immortalized hypertrophic chondrocytes. Thus, the normal decrease in bFGF responsiveness that accompanies chondrocyte hypertrophy may function in part by removing the potential for bFGF to induce PTHrP expression and to oppose the effects of BMPs. MCT cells may be useful in further understanding the mechanisms regulating the differentiation and function of hypertrophic chondrocytes.

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 α [GROα]) 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/GROα 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/GROα 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.

Many developmentally regulated membrane proteins of lymphocytes are ecto-enzymes, with their active sites on the external surface of the cell. These enzymes commonly have peptidase, phosphodiesterase or nucleotidase activity. Their biological roles are just beginning to be discovered. Although their expression is usually associated with particular stages of lymphoid differentiation, the same gene products are often expressed on the surface of certain non-lymphoid cell types outside the immune system, indicating that their functions cannot be unique to lymphocytes, nor can they be ubiquitous. The plasma cell membrane protein PC-1 (phosphodiesterase I; EC 3.1.4.1/nucleotide pyrophosphatase; EC 3.6.1.9), which was one of the first serological markers for lymphocyte subsets to be discovered, is a typical example. Within the immune system, PC-1 is confined to plasma cells, which represent about 0.1% of lymphocytes. However, PC-1 is also expressed on cells of the distal convoluted tubule of the kidney, chondrocytes, osteoblasts, epididymis and hepatocytes. Recent work has shown that PC-1 is a member of a multigene family of ecto-phosphodiesterases that currently has two other members, PD-1 alpha (autotaxin) and PD-1 beta (B10). Within this family, the extracellular domains are highly conserved, especially around the active site. In contrast, the transmembrane and cytoplasmic domains are highly divergent. Individual members of the eco-phosphodiesterase family have distinct patterns of distribution in different cell types, and even within the same cell. For example, PC-1 is present only on the basolateral surface of hepatocytes, while B10 (PD-1 beta) is confined to the apical surface. Analysis of conservation and differences in the sequence of their cytoplasmic tails may illuminate intracellular targetting signals. Ecto-phosphodiesterases may play a part in diverse activities in different tissues, including recycling of nucleotides. They may also regulate the concentration of pharmacologically active extracellular compounds such as adenosine or its derivatives and cell motility. Some members may modulate local concentrations of pyrophosphate, and hence influence calcification in bone and cartilage.

Chondrocytes exposed to nitric oxide (NO) or antibody to Fas undergo cell death by apoptosis. This study examines structural and functional properties of chondrocyte-derived apoptotic bodies. In NO treated cartilage, the dense pericellular matrix that normally surrounds the cells is degraded and apoptotic bodies accumulate within and in the vicinity of the chondrocyte lacunae. Functional analysis shows that apoptotic bodies isolated from NO-treated chondrocytes or cartilage produce pyrophosphate. The levels of pyrophosphate produced by apoptotic bodies are increased by pretreatment of the chondrocytes with transforming growth factor β and decreased by interleukin 1. Apoptotic bodies contain alkaline phosphatase and NTP pyrophosphohydrolase activities and can precipitate calcium. These results suggest that chondrocyte-derived apoptotic bodies express functional properties that may contribute to the pathologic cartilage calcification observed in aging and osteoarthritis.

Chronic macrophage-mediated inflammation is central to atherosclerosis. A role of the monocyte chemotactic and activating C-C chemokine JE/monocyte chemotactic protein-1 has been proposed. However, the human C-X-C chemokines growth-regulated oncogene (GROalpha) and IL-8, and their shared receptor, CXCR-2, also can be expressed at sites of chronic inflammation. Because we detected CXCR-2 in the intima of human atherosclerotic lesions, we examined the role of leukocyte CXCR-2 expression in affecting lesion cellularity. Atherosclerosis-susceptible LDL receptor-deficient mice were irradiated, successfully repopulated with bone marrow cells that either lacked or expressed mIL-8RH (the homologue of CXCR-2), and fed an atherogenic diet for 16 wk. In recipients of mIL-8RH+/+ marrow, mIL-8RH colocalized with densely accumulated intimal MOMA-2 positive macrophages. In contrast, lesions in recipients of mIL-8RH-/- marrow lacked mIL-8RH, had little intimal MOMA-2 staining, and were less extensive. The mIL-8RH ligand KC/GROalpha was detected in the intima of all aortic atherosclerotic lesions. Thus, the capacity of leukocytes to express mIL-8RH, and associated intralesional expression of its ligands such as KC/GROalpha, mediated the intimal accumulation of macrophages in atherosclerotic lesions of LDL receptor-deficient mice.

Our understanding of the participatory role of platelets in biologic processes other than hemostasis and coagulation is rapidly evolving. Platelets are implicated in the maintenance of capillary integrity and wound healing. Platelets may also contribute to the acceleration of atherogenesis, as the activation of these cells promotes vascular injury and platelets promote cholesterol accumulation within smooth muscle cells and macrophages. This chapter addresses the structure, function, and modes of activation of platelets as they relate to the potential role of these cells in certain immunologically mediated and inflammatory diseases in which alterations of blood vessel function and integrity occur.

The authors report that the nucleotide numbering for two mutations and one amino acid change in family 7 is not correct. The mutations c.2454G>C (p.Asp804His) and c.2496G>A (p.Arg821Pro) should correctly read as c.2410G>C (p.Asp804His) and c.2462G>A (p.Arg821His). Please note that the correct amino acid change at position 821 is Arginine to Histidine. Also, for families 8 and 9, nucleotide numbering for another mutation is listed incorrectly. c.2680C>T (p.Arg888Trp) should correctly read as c.2662C>T (p.Arg888Trp). The errors can be found in the Abstract, Table 1, and in Figure 1. © 2005 Wiley-Liss, Inc.

Background The IL-1 antagonist rilonacept demonstrated efficacy for gout flare (GF) prevention in patients (pts) initiating uric acid-lowering therapy (ULT) in two phase 3 trials of similar design (PRE-SURGE 1 and PRE-SURGE 2). Objectives To evaluate the efficacy and safety of subcutaneous rilonacept for GF prevention in various patient subpopulations using pooled data from these trials. Methods In both trials, pts with serum urate ≥7.5 mg/dL and ≥2 GFs within the past year who were initiating allopurinol were randomized to weekly treatment with rilonacept 80mg (R80), rilonacept 160mg (R160), or placebo (PBO). 16-week efficacy endpoints of GFs per pt and proportion of pts with ≥1 and ≥2 GFs were determined. Risk or rate ratios were estimated as treatment value divided by placebo value using generalized linear models and weighted for subgroup size; 1-risk ratio in percentage indicates relative risk reduction. Results Baseline characteristics were similar across treatment groups. The population was mainly male (93%), white (67%), and mean age was 51.7±12.3 yrs. By week 16, the R80 (n=162) and R160 (n=165) pts experienced GF rate reductions of 72%>76% relative to PBO (1.15 GFs per pt) (n=161) (both P Conclusions Pooled efficacy and safety data are consistent with those from the individual trials in demonstrating efficacy and tolerability of rilonacept for GF prevention in pts initiating ULT. Reductions in GFs were broadly observed regardless of demographic or clinical characteristics. Disclosure of Interest R. Evans Shareholder of: Regeneron Pharmaceuticals, Inc., Employee of: Regeneron Pharmaceuticals, Inc., R. Terkeltaub Grant/Research support from: Regeneron Pharmaceuticals, Inc., Consultant for: Regeneron Pharmaceuticals, Inc., E. Mitha Grant/Research support from: Regeneron Pharmaceuticals, Inc., J. Wang Shareholder of: Regeneron Pharmaceuticals, Inc., Employee of: Regeneron Pharmaceuticals, Inc., C. Barton Shareholder of: Regeneron Pharmaceuticals, Inc., Employee of: Regeneron Pharmaceuticals, Inc., H. Schumacher Grant/Research support from: Regeneron Pharmaceuticals, Inc., Consultant for: Regeneron Pharmaceuticals, Inc.

Background Patients (pts) with visible tophi and/or polyarticular disease (T/PD) may be at greater risk of gout flares (GFs) when initiating uric acid-lowering therapy (ULT). Objectives To determine the risk presented by T/PD for occurrence of GFs during initiation of ULT and to evaluate the efficacy of the IL-1 antagonist rilonacept for GF prevention in these pts using data from three Phase 3 clinical trials. Methods PRE-SURGE 1, PRE-SURGE 2, and RE-SURGE were randomized, double-blind, placebo (PBO)-controlled trials evaluating safety and efficacy of weekly SC doses of rilonacept 80mg (R80) and 160mg (R160) for prevention of GFs during initiation of ULT. Treatment duration was 16 wks. GF rate ratios were calculated in the PBO group for each study by comparing pts with T/PD vs pts without T/PD. GFs per pt and proportion of pts with ≥1 GF were estimated for pts with baseline serum urate ≥445 μmol/L (7.5 mg/dL), >2 GFs in the past year, and initiating allopurinol in each of the treatment groups within each study and pooled from the 3 studies. GFs were defined as pt-reported acute articular pain typical of a gout attack that required anti-inflammatory treatment. Results Pts with T/PD had significantly higher rates of GFs than those with monoarticular, non-tophaceous disease: GF rate ratios (95% confidence intervals) in PBO groups were 1.97 (1.02, 3.79), 3.69 (1.51, 9.02), and 1.93 (1.30, 2.86), in PRE-SURGE 1, PRE-SURGE 2, and RE-SURGE, respectively. Pooled data showed that for pts with T/PD, R80 resulted in a 69.5% reduction in mean number of GFs per pt vs PBO (from 1.81±2.52 [PB0] to 0.55±1.20 [R80]; P≤0.0001); the reduction with R160 was 67.7% (to 0.59±1.19; P≤0.0001). Reductions were generally similar to that observed in the total population. The proportions of pts with ≥1GF in the pooled T/PD population were 59.4%, 29.8%, and 30.7% for PBO, R80, and R160, respectively, almost a 50% reduction with rilonacept. For the total study population, the most commonly reported adverse event (AE), infections, was balanced among treatment groups; the most frequently reported treatment-related AE was injection site reaction. Conclusions The presence of T/PD represents a risk factor for GFs in pts initiating ULT. Among patients with these risk factors, rilonacept demonstrated efficacy for GF prevention that was generally similar to that of the overall population. Disclosure of Interest R. Evans Shareholder of: Regeneron Pharmaceuticals, Inc., Employee of: Regeneron Pharmaceuticals, Inc., H. Schumacher Grant/Research support from: Regeneron Pharmaceuticals, Inc., Consultant for: Regeneron Pharmaceuticals, Inc., R. Wu Shareholder of: Regeneron Pharmaceuticals, Inc., Employee of: Regeneron Pharmaceuticals, Inc., C. Barton Shareholder of: Regeneron Pharmaceuticals, Inc., Employee of: Regeneron Pharmaceuticals, Inc., R. Terkeltaub Grant/Research support from: Regeneron Pharmaceuticals, Inc., Consultant for: Regeneron Pharmaceuticals, Inc.

Background Most gout patients treated with 300 mg/d allopurinol do not reach the therapeutic goal range serum uric acid concentration (sUA) of

Hypercalcemia is commonly caused by the increased production of parathyroid hormone-related protein (PTHrP) by a malignancy. In fact, the demonstration of increased PTHrP production in a patient with hypercalcemia is virtually pathognomonic of malignancy. We studied a patient with systemic lupus erythematosus (SLE), generalized lymphadenopathy, and hypercalcemia. Immunohistology of 2 biopsied lymph nodes revealed the abundant expression of PTHrP and the absence of malignant transformation. Although apparently rare, PTHrP production by non-malignant lymphoid tissue may occur in SLE and should be considered in the differential diagnosis of hypercalcemia.

The optimal clinical management of patients with antiphospholipid antibody syndrome (APS) is uncertain because of a lack of an underlying hypothesis to explain why antiphospholipid autoantibodies (aPL) form to such ubiquitous compounds as phospholipids (PL). In this paper, we demonstrate that many, if not most, aPL are actually directed at neoepitopes of oxidized PL, or neoepitopes generated by adduct formation between breakdown products of oxidized PL and associated proteins. Each cardiolipin (CL) molecule contains four unsaturated fatty acids and is highly susceptible to oxidation, particularly upon exposure to air. Yet, standard anticardiolipin antibodies (aCL) immunoassays routinely bind CL to microtiter wells by evaporation of the ethanol solvent overnight at 4 degrees C. Using a variety of techniques, we demonstrated that rapid oxidation occurs when CL is plated and exposed to air. Sera from apo E-deficient mice, which have high autoantibody titers to oxidized low density lipoprotein, showed a striking time-dependent increase in binding to CL that was exposed to air for increasing periods of time. Monoclonal antibodies to oxidized LDL, cloned from the apo E-deficient mice, also bound to oxidized CL. Both sera and affinity-purified aCL-IgG from APS patients bound to CL progressively as it was oxidized. However, the monoclonal antibodies from apo E-deficient mice, or sera or aCL-IgG from APS patients did not bind to a reduced CL analog that was unable to undergo peroxidation. These data demonstrate that many aPL are directed at neoepitopes of oxidized phospholipids, and suggest that oxidative events may be important in the pathophysiology of APS. In turn, this suggests new therapeutic strategies, possibly including intensive antioxidant therapy.

Introduction In phase-3 clinical trials, the interleukin (IL-1) blocker, rilonacept (IL-1 Trap), demonstrated efficacy for gout flare prevention during initiation of urate-lowering therapy. This trial evaluated rilonacept added to a standard-of-care, indomethacin, for treatment of acute gout flares. Methods Adults, aged 18-70 years, with gout presenting within 48 hours of flare onset and having at least moderate pain as well as swelling and tenderness in the index joint were randomized to subcutaneous (SC) rilonacept 320 mg at baseline plus oral indomethacin 50 mg TID for 3 days followed by 25 mg TID for up to 9 days (n = 74); SC placebo at baseline plus oral indomethacin as above (n = 76); or SC rilonacept 320 mg at baseline plus oral placebo (n = 75). The primary efficacy endpoint was change in pain in the index joint (patient-reported using a Likert scale (0 = none; 4 = extreme)) from baseline to the average of values at 24, 48 and 72 hours (composite time point) for rilonacept plus indomethacin versus indomethacin alone. Comparison of rilonacept monotherapy with indomethacin monotherapy was dependent on demonstration of significance for the primary endpoint. Safety evaluation included clinical laboratory and adverse event (AE) assessments. Results Patient characteristics were comparable among the groups; the population was predominantly male (94.1%), white (75.7%), with mean ± SD age of 50.3 ± 10.6 years. All treatment groups reported within-group pain reductions from baseline (P < 0.0001). Although primary endpoint pain reduction was greater with rilonacept plus indomethacin (-1.55 ± 0.92) relative to indomethacin alone (-1.40 ± 0.96), the difference was not statistically significant (P = 0.33), so formal comparison between monotherapy groups was not performed. Pain reduction over the 72-hour period with rilonacept alone (-0.69 ± 0.97) was less than that in the other groups, but pain reduction was similar among groups at 72 hours. Treatment with rilonacept was well-tolerated with no reported serious AEs related to rilonacept. Across all groups, the most frequent AEs were headache and dizziness. Conclusions Although generally well-tolerated, rilonacept in combination with indomethacin and rilonacept alone did not provide additional pain relief over 72 hours relative to indomethacin alone in patients with acute gout flare. Trial registration ClinicalTrials.gov registration number NCT00855920.

Introduction AMP-activated protein kinase (AMPK) maintains cultured chondrocyte matrix homeostasis in response to inflammatory cytokines. AMPK activity is decreased in human knee osteoarthritis (OA) chondrocytes. Liver kinase B1 (LKB1) is one of the upstream activators of AMPK. Hence, we examined the relationship between LKB1 and AMPK activity in OA and aging cartilages, and in chondrocytes subjected to inflammatory cytokine treatment and biomechanical compression injury, and performed translational studies of AMPK pharmacologic activation. Methods We assessed activity (phosphorylation) of LKB1 and AMPKα in mouse knee OA cartilage, in aging mouse cartilage (6 to 24 months), and in chondrocytes after mechanical injury by dynamic compression, via immunohistochemistry or western blot. We knocked down LKB1 by siRNA transfection. Nitric oxide, matrix metalloproteinase (MMP)-3, and MMP-13 release were measured by Griess reaction and ELISA, respectively. Results Knockdown of LKB1 attenuated chondrocyte AMPK activity, and increased nitric oxide, MMP-3 and MMP-13 release (P

We aimed to describe the distribution of radiographic chondrocalcinosis (CC) and to examine whether metacarpophalangeal joint (MCPJ) calcification and CC at other joints occurs in the absence of knee involvement.This was a cross-sectional study embedded in the Genetics of Osteoarthritis and Lifestyle study (GOAL). All participants (n = 3,170) had radiographs of the knees, hands, and pelvis. These were scored for radiographic changes of osteoarthritis (OA), for CC at knees, hips, symphysis pubis, and wrists, and for MCPJ calcification. The prevalence of MCPJ calcification and CC overall, at each joint, and in the presence or absence of knee involvement, was calculated.The knee was the commonest site of CC, followed by wrists, hips, and symphysis pubis. CC was more likely to be bilateral at knees and wrists but unilateral at hips. MCPJ calcification was usually bilateral, and less common than CC at knees, hips, wrists, and symphysis pubis. Unlike that previously reported, CC commonly occurred without any knee involvement; 44.4% of wrist CC, 45.9% of hip CC, 45.5% of symphysis pubis CC, and 31.3% of MCPJ calcification occurred in patients without knee CC. Those with meniscal or hyaline articular cartilage CC had comparable ages (P = 0.21), and neither preferentially associated with fibrocartilage CC at distant joints.CC visualized on a plain radiograph commonly occurs at other joints in the absence of radiographic knee CC. Therefore, knee radiographs alone are an insufficient screening test for CC. This has significant implications for clinical practice, for epidemiologic and genetic studies of CC, and for the definition of OA patients with coexistent crystal deposition.

Objective In subjects with idiopathic calcium pyrophosphate dihydrate (CPPD) deposition disease, cartilage chondrocytes elaborate increased amounts of PPi. The mechanism of the intracellular PPi elevation is not known. Plasma membrane 5'-nucleotide phosphodiesterase I/nucleotide pyrophosphohydrolase (NTPPPH) activity also is elevated in chondrocytes and dermal fibroblasts of patients with idiopathic CPPD deposition disease. NTPPPH, as an ecto-enzyme, could act within certain intracellular compartments. Thus, we hypothesized a potential causal link between increased NTPPPH activity and increased intracellular PPi. Methods Transformed simian fibroblasts (COS cells) and human osteoblasts (U2OS cells) were transfected with the 5'-nucleotide phosphodiesterase I ecto-enzyme plasma cell membrane glycoprotein-1 (PC-1), recently shown to be expressed in cartilage, osteoblasts, and fibroblasts. Results Transfection with PC-1 markedly up-regulated 5'-nucleotode phosphodiesterase I activity and increased intracellular PPi concentrations by increasing the capacity of cells to generate PPi. Importantly, this did not require supplementation with exogenous nucleotides. Conclusion Cellular overexpression of PC-1 produces NTPPPH overactivity and increased intracellular PPi generation in vitro. These findings support the potential importance of NTPPPH overactivity in PPi generation, both inside and outside the cell, in some subjects with CPPD deposition disease.

Nat. Rev. Rheumatol. 6, 30–38 (2010); doi:10.1038/nrrheum.2009.236 In the Review article by Terkeltaub published in the January 2010 issue of Nature Reviews Rheumatology, the chemical structure of allopurinol included in Figure 2 was incorrect. The correct chemical structure is shown here.

Since last year's review of gout and hyperuricemia, investigators have described new potential mechanisms that may contribute to urate crystal deposition and the propagation, self-limitation, and therapeutic control of gouty inflammation. The clinical presentation of gout in women continues to be described in greater detail. Also, new information on oral allopurinol desensitization is now available to help approach the difficult problem of allopurinol hypersensitivity.

Nat. Med. 15, 641–644 (2010), published online 4 June 2010; corrected online 7 July 2010 In the version of this article initially published online, a reference was missing and a label was misplaced within the figure. The errors have been corrected for the PDF and HTML versions of this article.

The physical interaction of particulates with resident mononuclear phagocytes is a consistent feature in certain forms of crystal-induced inflammation. In this study, we observed that monosodium urate crystals stimulated the rapid release of neutrophil chemotactic activity from monocytes, and that this activity steadily increased over 24 hours. Because the release of monocyte-derived neutrophil chemotactic activity was markedly diminished by pretreatment of the monocytes with cycloheximide, and was completely removed from conditioned media by adsorption to heparin-agarose, we addressed the possibility that monocyte-derived neutrophil chemotactic factor/interleukin-8 (IL-8), a heparin-binding neutrophil-activating polypeptide, might modulate these activities. Urate crystal-induced IL-8 secretion from monocytes was verified by radioimmunoassay. In addition, an IL-8-specific antibody markedly inhibited the neutrophil-activating capacity of the conditioned media from monocytes activated by urate crystals, as well as by inflammatory silica crystals. Last, IL-8 was significantly increased in gouty synovial fluids (range 3.0-16.8 ng/ml, mean 8.4 ng/ml, n = 6) relative to osteoarthritic synovial fluids (range 1.1-1.7 ng/ml, mean 1.5 ng/ml, n = 6) (P = 0.006). We conclude that microcrystal-induced secretion of IL-8 by mononuclear phagocytes may mediate a number of forms of crystal-induced inflammation.

Factors that modulate the ability of monosodium urate crystals to stimulate leukocytes could regulate gouty inflammation. Lipoproteins that bear apo B-100 and apo E bind to urate crystals and suppress crystal-neutrophil interaction. In this study, we observed that urate crystals, coated with apo E of monocyte origin, had a diminished ability to stimulate neutrophils. Apo E was also detected on the surface of urate crystals recovered from gout patients. Thus, we analyzed apo E in noninflammatory synovial fluid, and found it to be associated with particles of heterogeneous size and of predominantly alpha and pre-beta electrophoretic mobility. Local articular synthesis of at least a portion of synovial fluid apo E was suggested because (a) the synovial fluid/plasma concentration ratio of apo E was significantly higher than that for both apo B and apo A-I, which are not widely synthesized by extrahepatic tissues, (b) cultured rheumatoid synovial cells in first passage secreted apo E, (c) a portion of synovial fluid apo E was heavily sialylated. We conclude that synovial fluids contain apo E that appears partly of local origin. Apo E binds to urate crystals and could modulate gouty inflammation.

Acute articular and periarticular inflammation and chronic articular destructive changes are well-recognized consequences of the deposition, in articular and periarticular tissues, of crystals of the monosodium salt of uric acid (MSU). MSU crystals directly or indirectly activate a remarkable number of humoral and cellular inflammatory mediator systems, and this is reflected in the clinical features of a typical acute gouty paroxysm, i. e., acute onset, severe pain, edema and erythema extending beyond the joint margin, neutro-phil influx and activation, and systemic manifestations. In this chapter, our current understanding of the pathogenesis of MSU-crystal-associated inflammation is reviewed.

Gouty arthritis is a characteristically intense acute inflammatory reaction that erupts in response to articular deposits of monosodium urate (MSU) crystals. Important recent molecular biologic advances in this field have given us a clear picture of the mechanistic basis of gouty inflammation. The innate immune inflammatory response is critically involved in the pathology of gout. Specifically, MSU crystals promote inflammation directly by stimulating cells via Toll-like receptor signaling and by providing a surface for cleavage of C5 and formation of complement membrane attack complex (C5b-9), culminating in secretion of cytokines, chemokines, and other inflammatory mediators with a dramatic influx of neutrophils into the joint. Despite the detailed mechanistic picture for gouty inflammation, there are no placebo-controlled, randomized clinical studies for any of the therapies commonly used, although comparative studies have demonstrated that many nonsteroidal anti-inflammatory drugs are equivalent to indomethacin with respect to controlling acute gouty attacks. In general, the first line of anti-inflammatory therapy for acute gout is nonsteroidal anti-inflammatory drugs, and the selective cyclo-oxygenase-2 inhibitor celecoxib can be used where appropriate. The second line of treatment is glucocorticosteroids, given systemically (oral, intravenous, or intramuscular) or intra-articularly. Alternatively, synthetic adrenocorticotropic hormone is effective, partly via induction of adrenal glucocorticosteroids and partly via rapid peripheral suppression of leukocyte activation by melatonin receptor 3 signaling. The third line of treatment is oral colchicine, which is highly effective when given early in an acute gouty attack, but it is poorly tolerated because of predictable gastrointestinal side effects.

Although dietary, genetic, or disease-related excesses in urate production may contribute to hyperuricemia, impaired renal excretion of uric acid is the dominant cause of hyperuricemia in the majority of patients with gout. The aims of this review are to highlight exciting and clinically pertinent advances in our understanding of how uric acid is reabsorbed by the kidney under the regulation of urate transporter (URAT)1 and other recently identified urate transporters; to discuss urate-lowering agents in clinical development; and to summarize the limitations of currently available antihyperuricemic drugs. The use of uricosuric drugs to treat hyperuricemia in patients with gout is limited by prior urolothiasis or renal dysfunction. For this reason, our discussion focuses on the development of the novel xanthine oxidase inhibitor febuxostat and modified recombinant uricase preparations.

Monosodium urate monohydrate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals cause acute gout and pseudogout, respectively. Because acute gout and pseudogout appear to be dependent on interleukin-8 (IL-8)-induced neutrophil ingress, this study was undertaken to define and compare how MSU and CPPD crystals stimulate IL-8 messenger RNA (mRNA) expression in mononuclear phagocytes.

A specific pattern of pericapitate involvement of the wrist has been described in the rheumatologic literature as characteristic of adult-onset Still disease (AOSD), a relatively rare disorder that is often diagnosed by exclusion after extensive and frequently invasive tests. To evaluate the potential diagnostic value of carpal radiography in suspected cases of AOSD, a retrospective blinded analysis of 48 patients (16 each with AOSD, juvenile chronic arthritis, and adult-onset rheumatoid arthritis) was performed. Pericapitate articular alterations without radiocarpal involvement were found to be distinctly unusual among patients with rheumatoid arthritis but frequent in the setting of AOSD. In juvenile chronic arthritis severe pericapitate involvement also occurs frequently but is more likely to be associated with interosseous fusion and severe pancompartmental disease.

Using 2-dimensional O'Farrell gel electrophoresis, we have mapped the proteins from undiluted plasma and serum which bind to monosodium urate (MSU) crystals. More than 30 crystal-associated polypeptides were visualized, including anionic and cationic species. Proteins increased on the crystals relative to plasma included C1q, C1-r, C1-s, fibronectin, fibrinogen, and kininogen. Crystal-bound polypeptides derived from IgG, albumin, and transferrin were recovered in decreased amounts relative to plasma. Direct evidence for activation of the complement and coagulation systems in plasma was provided by the identification of crystal-associated activation fragments of C1 and kininogen. Plasmas deficient in selected proteins (e.g., C1q and IgG) were used to define the role of these proteins in such activation events and confirmed activation of C1 in immunoglobulin-deficient plasma by MSU crystals. In summary, we have described a high resolution, semiquantitative approach to analyze protein binding to crystals, have documented the complexity of crystal-plasma protein interaction, and have provided direct evidence for the binding of coagulation system proteins and binding and activation of complement by MSU crystals, in whole plasma and IgG-deficient plasma.

Acute gout serves as a relatively well-defined paradigm for the review of the pathogenesis of acute microcrystal-induced inflammation. Inflammatory mediator systems activated directly or indirectly by urate crystals, the temporal events in a gouty paroxysm, and the possible factors responsible for the wide clinical variability of acute gout and other forms of crystal-induced inflammation are discussed.

Twenty-five patients with adult Still's disease were studied to determine clinical course and possible HLA associations. Two types of disease evolution were distinguishable clinically: a self-limited remitting disease with or without recurrent cyclic exacerbations was found in 11 patients, and a persistent disease with continuous activity for more than 1 year, generally accompanied by progressive joint disease, was determined in 8. Disease course could not be classified in 6 patients. The antigen frequencies of HLA-Bw35 (40%, P less than 0.05) and Cw4 (44%, P less than 0.05) were increased in adult Still's disease as compared to controls (18% and 20%, respectively). Because HLA-Bw35 was associated with self-limited remitting type disease (P less than 0.02), this antigen may be a favorable prognostic marker in adult Still's disease.

Low density lipoprotein (LDL) is the major plasma inhibitor of neutrophil oxidative and lytic responses to monosodium urate crystals and may function to modulate acute gouty inflammation. LDL inhibited apparent phagocytosis of urate crystals by human neutrophils, suggesting it may interfere with early events in the crystal-induced stimulation of neutrophils. The effects were not specific for neutrophils, since human platelet secretory and membranolytic responses to urate crystals were also inhibited by purified LDL in doses as low as 10 micrograms/ml. As with neutrophils, the inhibitory activity of LDL was stimulus-specific. Since LDL binds to urate crystals and specifically inhibits a range of cellular responses to them, including phagocytosis, we hypothesized that LDL interferes with the initial crystal-cell interaction. We measured platelet interaction with urate crystals and found that LDL was a potent inhibitor of crystal-induced platelet sedimentation and was 10-100-fold more active than lipoprotein-depleted plasma or purified high density lipoprotein. In summary, LDL inhibits a broad range of responses of a number of inflammatory cell types to certain inflammatory surfaces, and this effect appears to be due to inhibition of physical association of crystals with cell membranes.