Crystal-neutrophil interactions lead to interleukin-1 synthesis

Monosodium Urate Crystal-Induced Pyroptotic Cell Death in Neutrophil and Macrophage Facilitates the Pathological Progress of Gout

Monosodium urate (MSU) crystal deposition in joints can lead to the infiltration of neutrophils and macrophages, and their activation plays a critical role in the pathological progress of gout. However, the role of MSU crystal physicochemical properties in inducing cell death in neutrophil and macrophage is still unclear. In this study, MSU crystals of different sizes are synthesized to explore the role of pyroptosis in gout. It is demonstrated that MSU crystals induce size-dependent pyroptotic cell death in bone marrow-derived neutrophils (BMNs) and bone marrow-derived macrophages (BMDMs) by triggering NLRP3 inflammasome-dependent caspase-1 activation and subsequent formation of N-GSDMD. Furthermore, it is demonstrated that the size of MSU crystal also determines the formation of neutrophil extracellular traps (NETs) and aggregated neutrophil extracellular traps (aggNETs), which are promoted by the addition of interleukin-1β (IL-1β). Based on these mechanistic understandings, it is shown that N-GSDMD oligomerization inhibitor, dimethyl fumarate (DMF), inhibits MSU crystal-induced pyroptosis in BMNs and J774A.1 cells, and it further alleviates the acute inflammatory response in MSU crystals-induced gout mice model. This study elucidates that MSU crystal-induced pyroptosis in neutrophil and macrophage is critical for the pathological progress of gout, and provides a new therapeutic approach for the treatment of gout.

The PRY/SPRY domain of pyrin/TRIM20 interacts with β2-microglobulin to promote inflammasome formation

Pyrin/TRIM20 is expressed in the neutrophils and monocytes/macrophages and regulates caspase-1 activation and interleukin-1β maturation. Although the mutations in the PRY/SPRY domain of pyrin cause familial Mediterranean fever (FMF), the mechanism of how mutated pyrin provokes excessive inflammation in FMF patients is not well understood. The present study investigated the role of pyrin/TRIM20 in inflammation and the pathogenesis of FMF. β₂-Microglobulin (β2MG) was identified as the novel pyrin ligand binding to the PRY/SPRY domain by yeast two-hybrid screenings and co-immunoprecipitation analysis. β2MG was co-localized with pyrin not only in the HEK293 cells overexpressing these proteins but also in the monosodium urate-stimulated human neutrophils in the speck-like structures. The pyrin–β2MG interaction triggered the binding of pyrin and proline–serine–threonine phosphatase interacting protein 1 (PSTPIP1) and then the subsequent recruitment of apoptosis-associated speck-like protein containing caspase recruitment domain (ASC). Caspase-1 p20 subunit, produced by pyrin inflammasome, also interacted with the pyrin PRY/SPRY domain and inhibited the pyrin–β2MG interaction. FMF-associated pyrin mutation M694V did not affect pyrin–β2MG interaction but weakened this inhibition. Our findings suggest that β2MG functions as the pyrin ligand inducing pyrin inflammasome formation and that the FMF-associated pyrin mutations weakened negative feedback of caspase-1 p20 subunit.

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.

Effect of pathogenic crystals on the production of pro- and anti-inflammatory cytokines by different leukocyte populations

PURPOSE

To evaluate cytokine production in vitro by different types of leukocytes stimulated with monosodium urate (MSU), calcium pyrophosphate (CPP) and basic calcium phosphate (BCP) crystals.

MATERIAL AND METHODS

Polymorphonuclear cells (PMN), monocytes and lymphocytes, isolated from healthy volunteer blood, were stimulated for different time periods with increasing MSU, CPP or BCP crystal concentrations. IL-1β, IL-8, IL-6, CCL2, IL-1Ra and TGFβ1 were determined by ELISA.

RESULTS

Exposure of PMN to different crystals resulted in a moderate IL-8 and IL-1Ra release. Stimulation of monocytes induced a significant production of all the cytokines evaluated. The highest levels of IL-1β, IL-6, CCL2 and IL-8 were observed with MSU at 0.5 mg/ml, CPP at 0.01-0.05 mg/ml and BCP at 1 mg/ml after 18-48 h and then decreased. At the same crystal concentrations, IL-1Ra and TGFβ1 increased until the end of the experiment. Treatment of lymphocytes with different crystals did not induce cytokine release.

CONCLUSION

This study demonstrates that PMN, monocytes and lymphocytes from the same donor respond differently after stimulation with MSU, CPP or BCP crystals, depending on the dose and the time of exposure. Crystals induce a rapid increase of pro-inflammatory cytokines, whereas longer time is required to release high levels of anti-inflammatory cytokines.

Tu-Teng-Cao Extract Alleviates Monosodium Urate-Induced Acute Gouty Arthritis in Rats by Inhibiting Uric Acid and Inflammation

Gouty arthritis is an inflammatory joint disease closely related to hyperuricemia. It is characterized by deposition of monosodium urate crystals in the joints, resulting in an intense inflammatory process and pain. Control of hyperuricemia and anti-inflammation treatments are the main therapeutic approaches. However, the commonly used drugs for inhibiting uric acid and acute gouty arthritis have obvious gastrointestinal and renal toxicity; thus, there is an urgency to develop new alternative therapeutic drugs. An extract of Tu-Teng-Cao (TTC), a compound drug used in traditional Chinese medicine, has been widely applied to the clinical treatment of arthritis. In this study, we investigated the therapeutic effects of TTC on gouty arthritis. In this study, an animal model of acute gouty arthritis with hyperuricemia was established using potassium oxonate and monosodium urate crystals. After treatment with TTC, the results showed obvious therapeutic effects on the rat model of acute gouty arthritis. The treatment significantly attenuated the degree of ankle swelling, inflammation, and dysfunction index, and the levels of proinflammatory cytokines. In addition, TTC has significant antihyperuricemia activity in rats with hyperuricemia induced by potassium oxonate. Histological evaluation showed that TTC relieved pathological damage in rats with acute gouty arthritis induced by monosodium urate crystals. All the groups treated with TTC showed improvement in cartilage degeneration, cell degeneration, synovial hyperplasia, and inflammatory cell invasion in the ankle joint of rats. TTC significantly alleviated swelling, inflammation, and bleeding of the renal corpuscle and convoluted tubules of rats. The results of this study suggest that TTC is capable of treating gouty arthritis and decreasing ankle injury through the control of uric acid and inflammation.

Cytokine Production and NET Formation by Monosodium Urate-Activated Human Neutrophils Involves Early and Late Events, and Requires Upstream TAK1 and Syk

Gout is a prevalent and incapacitating disease triggered by the deposition of monosodium urate (MSU) crystals in joints, which are also massively infiltrated by neutrophils. The interaction of the latter with MSU crystals triggers several responses, including the generation of inflammatory mediators and of neutrophil extracellular traps (NETs). Though some of the signaling events mobilized by MSU in neutrophils have been described (e.g., Src family kinases, Syk, PKC, PI3K), the picture remains fragmentary. Likewise, the impact of these signaling events on cellular responses is incompletely understood. In this study, we examined transcriptomic changes triggered by MSU in neutrophils and their impact on the corresponding proteins, as well as the role of various signaling pathways in prominent functional responses. We report for the first time that neutrophils can secrete the monocyte chemoattractant, CCL4, in response to MSU. Accordingly, we found that transcription factors NF-κB, CREB, and C/EBP are belatedly activated by MSU crystals, and at least the former is involved in chemokine generation. Moreover, we show that MAPKs and Akt are activated by MSU in neutrophils, that they are under the control of TAK1 and Syk, and that they participate in cytokine generation and NETosis. In the latter instance, we found the phenomenon to be independent of endogenous ROS, but under the control of PAD4. We finally provide evidence that endogenous factors contribute to the belated phosphorylation of kinases and transcription factors in response to MSU. Collectively, our findings unveil potentially important therapeutic targets for gouty arthritis.

A Beacon in the Dark: Canakinumab. A New Therapeutic Perspective in Chronic Tophaceous Gout

Gout is the most common form of arthritis in adults. It is often associated with other comorbidities, which contraindicate the use of conventional therapies. The discovery of the role of interleukin-1β (IL-1β) in orchestrating the monosodium urate crystal-induced inflammatory response offered new therapeutic prospects to refractory patients, or to those in whom standard therapies are contraindicated. This paper describes a clinical case of a 65-year-old man with chronic tophaceous gouty arthropathy and subintrant flares, who had comorbidities contraindicating the use of conventional gout therapies-to which he did not respond-who was treated with canakinumab, a monoclonal selective inhibitor of IL-1β. The patient reported a gradual, rapid, and significant reduction in pain, with a response observed within 12 h of the administration of the drug. Consistent with previous clinical studies, canakinumab appeared to be a viable, safe, and effective alternative to conventional therapies in this patient with gout who had limited therapeutic options.

FUNDING

Novartis Farma, Italy.

A Beacon in the Dark: Canakinumab. A New Therapeutic Perspective in Chronic Tophaceous Gout

Gout is the most common form of arthritis in adults. It is often associated with other comorbidities, which contraindicate the use of conventional therapies. The discovery of the role of interleukin-1β (IL-1β) in orchestrating the monosodium urate crystal-induced inflammatory response offered new therapeutic prospects to refractory patients, or to those in whom standard therapies are contraindicated. This paper describes a clinical case of a 65-year-old man with chronic tophaceous gouty arthropathy and subintrant flares, who had comorbidities contraindicating the use of conventional gout therapies-to which he did not respond-who was treated with canakinumab, a monoclonal selective inhibitor of IL-1β. The patient reported a gradual, rapid, and significant reduction in pain, with a response observed within 12 h of the administration of the drug. Consistent with previous clinical studies, canakinumab appeared to be a viable, safe, and effective alternative to conventional therapies in this patient with gout who had limited therapeutic options.

FUNDING

Novartis Farma, Italy.

A Role for Gut Microbiota and the Metabolite-Sensing Receptor GPR43 in a Murine Model of Gout

OBJECTIVE

Host-microbial interactions are central in health and disease. Monosodium urate monohydrate (MSU) crystals cause gout by activating the NLRP3 inflammasome, leading to interleukin-1β (IL-1β) production and neutrophil recruitment. This study was undertaken to investigate the relevance of gut microbiota, acetate, and the metabolite-sensing receptor GPR43 in regulating inflammation in a murine model of gout.

METHODS

Gout was induced by the injection of MSU crystals into the knee joints of mice. Macrophages from the various animals were stimulated to determine inflammasome activation and production of reactive oxygen species (ROS).

RESULTS

Injection of MSU crystals caused joint inflammation, as seen by neutrophil influx, hypernociception, and production of IL-1β and CXCL1. These parameters were greatly decreased in germ-free mice, mice treated with antibiotics, and GPR-43-deficient mice. Recolonization or administration of acetate to germ-free mice restored inflammation in response to injection of MSU crystals. In vitro, macrophages produced ROS and assembled the inflammasome when stimulated with MSU. Macrophages from germ-free animals produced little ROS, and there was little inflammasome assembly. Similar results were observed in macrophages from GPR-43-deficient mice. Treatment of germ-free mice with acetate restored in vitro responsiveness of macrophages to MSU crystals.

CONCLUSION

In the absence of microbiota, there is decreased production of short-chain fatty acids that are necessary for adequate inflammasome assembly and IL-1β production in a manner that is at least partially dependent on GPR43. These results clearly show that the commensal microbiota shapes the host's ability to respond to an inflammasome-dependent acute inflammatory stimulus outside the gut.

Dolichos falcata Klein attenuated the inflammation induced by monosodium urate crystals in vivo and in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Dolichos falcata Klein (DF), a Chinese Dai ethnic medicine popularly known as "Tuoyeteng" in Yunnan province of China, has been widely used as a traditional herbal medicine for the treatment of fracture and beriberoid disease for a long time in China. The present study was carried out to investigate the anti-inflammatory activity and the bioactive chemical constituents of DF, and further to assess its possible mechanism on gouty arthritis in an animal model of the MSU crystals-induced gouty inflammation.

MATERIALS AND METHODS

The ethanol extract (EE) of DF at the doses of 10, 20 and 40 mg/kg was administered to the rats treated with MSU crystals to evaluate the anti-gouty arthritis effect. Subsequently, the components of EE were isolated and identified using classical methods. Phyto-chemical analysis of EE was further carried out by HPLC-DAD. Finally, the anti-inflammatory effect of EE and two isolated components were assessed using the MSU crystals-treated monocyte/macrophage cell line RAW 264.7 in vitro.

RESULTS

EE (10, 20 and 40 mg/kg) significantly attenuated the pain threshold value, the joint swelling degree, the inflammatory cell infiltration of articular tissue and the increased levels of pro-inflammatory cytokines in MSU crystals-treated rats. Moreover, doliroside A (DA) and medicagenic acid-3-O-β-D-glucopyranoside (MG) were isolated and identified from EE. The major components of EE, including DA, MG and other triterpenoids, were well confirmed by HPLC. A further study revealed that EE, DA and MG (10, 20, 40μg/mL) exhibited stronger inhibitory effects on the production of pro-inflammatory cytokines (including interleukin-1β, interleukin-6 and tumor necrosis factor-α) in MSU crystals-treated RAW 264.7 cells.

CONCLUSION

These findings indicate that the major triterpenoids present in DF have a remarkable effect on improving symptoms of acute gouty arthritis induced by MSU crystals through inhibiting the production of pro-inflammatory cytokines.

NLRP3 inflammasome-mediated neutrophil recruitment and hypernociception depend on leukotriene B(4) in a murine model of gout

OBJECTIVE

Deposition of monosodium urate monohydrate (MSU) crystals in the joints promotes an intense inflammatory response and joint dysfunction. This study evaluated the role of the NLRP3 inflammasome and 5-lipoxygenase (5-LOX)-derived leukotriene B(4) (LTB(4) ) in driving tissue inflammation and hypernociception in a murine model of gout.

METHODS

Gout was induced by injecting MSU crystals into the joints of mice. Wild-type mice and mice deficient in NLRP3, ASC, caspase 1, interleukin-1β (IL-1β), IL-1 receptor type I (IL-1RI), IL-18R, myeloid differentiation factor 88 (MyD88), or 5-LOX were used. Evaluations were performed to assess neutrophil influx, LTB(4) activity, cytokine (IL-1β, CXCL1) production (by enzyme-linked immunosorbent assay), synovial microvasculature cell adhesion (by intravital microscopy), and hypernociception. Cleaved caspase 1 and production of reactive oxygen species (ROS) were analyzed in macrophages by Western blotting and fluorometric assay, respectively.

RESULTS

Injection of MSU crystals into the knee joints of mice induced neutrophil influx and neutrophil-dependent hypernociception. MSU crystal-induced neutrophil influx was CXCR2-dependent and relied on the induction of CXCL1 in an NLRP3/ASC/caspase 1/IL-1β/MyD88-dependent manner. LTB(4) was produced rapidly after injection of MSU crystals, and this was necessary for caspase 1-dependent IL-1β production and consequent release of CXCR2-acting chemokines in vivo. In vitro, macrophages produced LTB(4) after MSU crystal injection, and LTB(4) was relevant in the MSU crystal-induced maturation of IL-1β. Mechanistically, LTB(4) drove MSU crystal-induced production of ROS and ROS-dependent activation of the NLRP3 inflammasome.

CONCLUSION

These results reveal the role of the NLRP3 inflammasome in mediating MSU crystal-induced inflammation and dysfunction of the joints, and highlight a previously unrecognized role of LTB(4) in driving NLRP3 inflammasome activation in response to MSU crystals, both in vitro and in vivo.

Monosodium urate monohydrate crystal-recruited noninflammatory monocytes differentiate into M1-like proinflammatory macrophages in a peritoneal murine model of gout

OBJECTIVE

To profile monosodium urate monohydrate (MSU) crystal-recruited monocyte inflammatory function during the course of in vivo differentiation, in a murine model of peritoneal MSU crystal-induced inflammation.

METHODS

C57BL/6J mice were injected intraperitoneally with MSU crystals, and the peritoneal cells were harvested at different time points. The MSU crystal-recruited monocyte/macrophage population was analyzed for the expression of differentiation and activation markers, cytokine production following MSU crystal restimulation ex vivo and in vivo, expression of NLRP3-associated proteins (ASC, caspase 1) and pro-interleukin-1β (proIL-1β), and phagocytic capacity.

RESULTS

Monocytes recruited 8 hours after MSU crystal stimulation (F4/80(low) Gr-1(int) 7/4+) exhibited poor phagocytic capacity, expressed low levels of proIL-1β, and failed to produce proinflammatory cytokines in response to MSU crystal restimulation. In the absence of MSU crystal restimulation, differentiating monocytes produced low levels of transforming growth factor β1 ex vivo, and this was abrogated following MSU crystal restimulation. Over time these cells developed a proinflammatory phenotype in vivo, characterized by the production of IL-1β, tumor necrosis factor α, IL-6, CCL2 (monocyte chemotactic protein 1), and CXCL1 (cytokine-induced neutrophil chemoattractant) following ex vivo MSU crystal restimulation, and leading to IL-1β production and cell infiltration following MSU crystal rechallenge in vivo. Proinflammatory function was associated with differentiation toward a macrophage phenotype (F4/80(high) Gr-1-7/4-), an increase in phagocytic capacity, and an increase in the expression of proIL-1β.

CONCLUSION

MSU crystal-recruited monocytes differentiate into proinflammatory M1-like macrophages in vivo. This proinflammatory macrophage phenotype is likely to play a key role in perpetuating inflammation in gouty arthritis in the presence of ongoing deposition of fresh MSU crystals.

Characterization of cytolytic neutrophil activation in vitro by amorphous hydrated calcium phosphate as a model of biomaterial inflammation

Calcium ions are utilized in biomolecular biomaterial design for osteomimetic scaffolds and as divalent cross-linking agents, typically for gelation of alginates, stabilisation of protein structure (e.g., fibrinogen) and enzyme activation (e.g., thrombin). Biological interactions with defined calcium phosphates (e.g., hydroxyapatite) are exploited for osteogenesis, although crystalline calcium phosphates (e.g., calcium pyrophosphate) stimulate inflammation. We found that the calcium concentration used in the manufacture of prototype dermal scaffolds made from fibrin/alginate composite was related to the inflammatory infiltration during in vivo integration. In investigating a cause for this inflammatory response, we have identified and characterized a cytolytic inflammatory effect of amorphous calcium phosphate (CaP) formed in physiological solutions, relevant to biomaterial biocompatibility. Isolated human neutrophils (Nφ) were incubated in phosphate-buffered saline with CaCl(2) ranging 2.5-20 mM total calcium. Nφ activation was assessed by morphology and integrin-β2 (CD18a) expression. Mediator release (Nφ-elastase, IL-8, and TNFα) was measured from both Nφ and whole blood cultures plus CaCl(2). CaP exposure increased CD18a expression over 1 h (maximal at 10 mM calcium/ phosphate) with concurrent phagocytosis, cytolysis, and Nφ-elastase release. CaCl(2) induced expression of IL-8 and TNFα in whole blood cultures. These results suggest that CaP formed from the resorption of calcium-containing biomaterials could induce inflammation and accelerate biomaterial degradation, driving further CaP release. This demonstrates a novel mechanism for biomaterial-induced inflammation. The in vitro system described could aid preclinical evaluation of novel biomaterial inflammatory potential.

The sterile inflammatory response

The acute inflammatory response is a double-edged sword. On the one hand, it plays a key role in initial host defense, particularly against many infections. On the other hand, its aim is imprecise, and as a consequence, when it is drawn into battle, it can cause collateral damage in tissues. In situations where the inciting stimulus is sterile, the cost-benefit ratio may be high; because of this, sterile inflammation underlies the pathogenesis of a number of diseases. Although there have been major advances in our understanding of how microbes trigger inflammation, much less has been learned about this process in sterile situations. This review focuses on a subset of the many sterile stimuli that can induce inflammation-specifically dead cells and a variety of irritant particles, including crystals, minerals, and protein aggregates. Although this subset of stimuli is structurally very diverse and might appear to be unrelated, there is accumulating evidence that the innate immune system may recognize them in similar ways and stimulate the sterile inflammatory response via common pathways. Here we review established and emerging data about these responses.

Crystal-induced neutrophil activation: XI. Implication and novel roles of classical protein kinase C

Monosodium urate (MSU) crystals are among the most potent proinflammatory stimuli, and an innate immune inflammatory response to the crystal surface is involved in the pathology of gouty arthritis. Furthermore, MSU crystals have recently been identified as danger signals able to induce the maturation of dendritic cells. Release of the crystals into the joint cavity promotes an acute inflammation characterized by a massive infiltration of neutrophils that leads to tissue damage. Protein kinase C (PKC) represents a family of serine/threonine kinases that play central signaling roles in multiple cellular responses. This family of kinases is divided into three subfamilies based on second messenger requirements: conventional (or classical), novel, and atypical. Despite their role in signal transduction, very little is known about the involvement of the PKC family in the inflammatory reaction induced by MSU crystals. In the present study, we show that MSU crystals activate conventional PKC isoforms, and that this activation is necessary for the MSU crystal-induced degranulation and generation of a chemotactic activity in the supernatants of MSU crystal-stimulated human neutrophils. Evidence is also obtained that the tyrosine kinase Syk is a substrate of PKC and that the PKC-mediated serine phosphorylation of Syk is necessary to its interaction with the regulatory subunit of PI3K kinases (p85) and thus to the subsequent activation of these lipid kinases. These results suggest novel means of modulating neutrophil responses (through the specific regulation of PKC) during the acute phase of MSU crystal-induced inflammation.

Crystal-induced neutrophil activation: X. Proinflammatory role of the tyrosine kinase Tec

OBJECTIVE

Monosodium urate monohydrate (MSU) crystals are among the most potent proinflammatory stimuli, and an innate immune inflammatory response to the crystal surface is involved in the pathogenesis of gouty arthritis. Release of the crystals into the joint cavity promotes an acute inflammation characterized by massive infiltration of neutrophils, which leads to tissue damage. The aim of the present study was to assess the involvement of the tyrosine kinase Tec in MSU crystal-initiated transduction events in human neutrophils.

METHODS

Immunoprecipitation and immunoblotting techniques were used for the cellular signaling studies. Chemotaxis and enzyme-linked immunosorbent assay techniques were used for the functional studies. Silencing of Tec expression using specific small interfering RNA was also performed.

RESULTS

MSU crystals induced the phosphorylation and activation of Tec in a Src-dependent manner. This activation was necessary for the MSU crystal-induced secretion of interleukin-1beta (IL-1beta) and IL-8 and for the generation of chemotactic activity in supernatants of MSU crystal-stimulated neutrophils. In addition, colchicine, an effective drug for the treatment of gout, inhibited the MSU crystal-induced tyrosine phosphorylation of Tec, thus modulating its kinase activity.

CONCLUSION

Our findings show that Tec is the principal kinase of the Tec family that plays a major role in the responses of human neutrophils to MSU crystals, which are likely to be involved in the initiation and perpetuation of gout. Our results suggest that the specific inhibition of Tec during the acute phase of MSU crystal-induced inflammation may be considered for the treatment of gouty arthritis.

MyD88-dependent IL-1 receptor signaling is essential for gouty inflammation stimulated by monosodium urate crystals

While it is known that monosodium urate (MSU) crystals cause the disease gout, the mechanism by which these crystals stimulate this inflammatory condition has not been clear. Here we find that the Toll/IL-1R (TIR) signal transduction adaptor myeloid differentiation primary response protein 88 (MyD88) is required for acute gouty inflammation. In contrast, other TIR adaptor molecules, TIRAP/Mal, TRIF, and TRAM, are not required for this process. The MyD88-dependent TLR1, -2, -4, -6, -7, -9, and -11 and IL-18 receptor (IL-18R) are not essential for MSU-induced inflammation. Moreover, MSU does not stimulate HEK cells expressing TLR1-11 to activate NF-kappaB. In contrast, mice deficient in the MyD88-dependent IL-1R showed reduced inflammatory responses, similar to those observed in MyD88-deficient mice. Similarly, mice treated with IL-1 neutralizing antibodies also showed reduced MSU-induced inflammation, demonstrating that IL-1 production and IL-1R activation play essential roles in MSU-triggered inflammation. IL-1R deficiency in bone marrow-derived cells did not affect the inflammatory response; however, it was required in non-bone marrow-derived cells. These results indicate that IL-1 is essential for the MSU-induced inflammatory response and that the requirement of MyD88 in this process is primarily through its function as an adaptor molecule in the IL-1R signaling pathway.

Intracellular and extracellular CPPD crystals are a regular feature in synovial fluid from uninflamed joints of patients with CPPD related arthropathy

OBJECTIVES

To determine whether calcium pyrophosphate dihydrate (CPPD) crystals can be found in the synovial fluid of non-inflamed joints in patients with CPPD related arthropathy; if so, to determine whether they interact with cells and produce subclinical inflammation in this setting.

METHODS

74 synovial fluid samples were obtained from non-inflamed knees of 74 patients with CPPD related arthropathy. Identification of CPPD crystals and synovial fluid cell counts were done manually in undiluted samples using a haematocytometric chamber. A supravital stain (Testsimplets, Boehringer Mannheim) was used to carry out differential counts and to assess the presence of intracellular crystals.

RESULTS

All 74 samples contained CPPD crystals. The mean cell count was 301.4 cells/microl (95% confidence interval (CI), 216.6 to 386.4; range 22 to 2302.5). Mononuclear cells accounted for 83.2% (95% CI, 80.4% to 86.1%; range 43% to 99%), the rest being polymorphonuclear (PMN) cells (16.8% (95% CI, 13.9% to 19.6%; range 1% to 57%)). All the samples contained intracellular CPPD crystals, which were found in 24.0% of all the cells (95% CI, 20.1% to 27.9%; range 1% to 78%). Most of the intracellular crystals were inside mononuclear cells (22.2% of all the cells (95% CI, CI 18.5% to 25.9%)), although some PMN also contained them (1.8% of all the cells (95% CI, 1.1% to 2.4%)).

CONCLUSIONS

CPPD crystals are normally found in synovial fluid of non-inflamed joints of patients with CPPD related arthropathy, and they interact with cells. The raised cell counts and percentage of PMN suggest mild subclinical inflammation in these joints.

Update on colchicine and its mechanism of action

Colchicine is a unique anti-inflammatory drug with respect to its limited clinical usefulness and its mode of action. Colchicine is mainly indicated for the treatment and prophylaxis of gout and familial Mediterranean fever. Its mode of action includes modulation of chemokine and prostanoid production and inhibition of neutrophil and endothelial cell adhesion molecules by which it interferes with the initiation and amplification of the joint inflammation. This paper discusses its adverse effects and indications.

Inflammatory microcrystals alter the functional phenotype of human osteoblast-like cells in vitro: synergism with IL-1 to overexpress cyclooxygenase-2

Chronic crystal-associated arthropathies such as gout and pseudogout can lead to local bone destruction. Because osteoblasts, which orchestrate bone remodeling via soluble factors and cell-to-cell interactions, have been described in contact with microcrystals, particularly in uratic foci of gout, we hypothesized that microcrystals of monosodium urate monohydrate (MSUM) and of calcium pyrophosphate dihydrate (CPPD) could alter osteoblastic functions. MSUM and CPPD adhered to human osteoblastic cells (hOB) in vitro and were partly phagocytized as shown by scanning electron microscopy. MSUM and CPPD dose-dependently stimulated the production of PGE(2) in hOB as assessed by enzyme immunoassay, a response that was synergistically enhanced in the presence of IL-1. The mechanism of this synergism was, at least in part, at the level of the expression of cyclooxygenase-2 as evaluated by immunoblot analysis. MSUM and CPPD also stimulated the expression of IL-6 and IL-8 and reduced the 1,25-dihydroxyvitamin D(3)-induced activity of alkaline phosphatase and osteocalcin in hOB (with no synergism with IL-1). MSUM- or CPPD-stimulated expression of IL-6 in hOB pretreated with the selective cyclooxygenase-2 inhibitor NS-398 was increased, unlike that induced by IL-1 alone which was partially reduced. MSUM-, CPPD- or IL-1-induced expression of IL-8 was unchanged by pretreating hOB with NS-398. These results suggest that inflammatory microcrystals alter the normal phenotype of hOB, redirecting them toward reduced bone formation and amplified osteoblast-mediated bone resorption, abnormalities that could play a role in the bone destruction associated with chronic crystal-induced arthritis.

Evidence for a role for SAM68 in the responses of human neutrophils to ligation of CD32 and to monosodium urate crystals

SAM68 (Src-associated in mitosis 68 kDa) is a member of the signal transduction of activator RNA novel gene family coding for proteins postulated to be involved in signal transduction and activation of RNA. It has been implicated through its phosphorylation status in the control of the transition from the G(1) to the S phases during mitosis. However, the implication and role of SAM68 in nonproliferative cells are unknown. The present study was initiated to examine the role of SAM68 in the phagocytic responses of the terminally differentiated human neutrophils. The results obtained show that SAM68 is present in human neutrophils and that it is tyrosine phosphorylated in response to stimulation by monosodium urate crystals or by ligation of CD32. Stimulation of neutrophils by these agonists decreases the association of SAM68 with Sepharose-conjugated poly-U beads. Additionally, the amount of immunoprecipitable SAM68 was modulated differentially after stimulation by monosodium urate crystals or by CD32 engagement indicating that the posttranslational modifications and/or protein associations of SAM68 induced by these two agonists differed. The results of this study provide evidence for an involvement of SAM68 in signal transduction by phagocytic agonists in human neutrophils and indicate that SAM68 may play a role in linking the early events of signal transduction to the posttranscriptional modulation of RNA.

Reperfusion injury after focal myocardial ischaemia: polymorphonuclear leukocyte activation and its clinical implications

The only way to rescue ischaemic tissue is to re-instate the oxygen supply to the tissue. However reperfusion of the ischaemic area not only oxygenates the tissue but also initiates a cascade of processes, which may in some cases result in temporary dysfunction of the myocardium. In order to devise protective measures, it is essential to understand the mechanisms and the triggers of this reperfusion phenomenon. In this review we will mainly focus on the inflammatory response caused by reperfusion. We will cover the different steps of polymorphonuclear leukocyte activation and will briefly discuss the molecular biology of the receptors involved. The currently used pharmacological medications in acute cardiology will be reviewed and in particular their actions on polymorphonuclear leukocyte activation, adhesion and degranulation. This review is a compilation of the current knowledge in the field and the therapeutic progress in the prevention of reperfusion injury made today.

Colcemid alters S phase and other parameters in skin during chronic exposure to benzo(a)pyrene

The administration of Colcemid for collecting mitotic figures in a carcinogenesis study, using benzo(a)pyrene (BaP), diminished the experimental differences between exposed and control mice. A dose-related increase in noncollected mitotic index (n-mitotic index) was seen in keratinocytes in the dorsal epidermis of mice which received four weekly treatments of BaP at 16, 32 and 64 micrograms in 50 microliters of acetone. In contrast, the number of mitotic figures collected for 4 hr by Colcemid block (c-mitotic index) was depressed at 16 micrograms, unchanged at 32 micrograms, and elevated at 64 micrograms of BaP. Weekly treatments with 4,8 or 16 micrograms BaP for 3-8 months induced an elevation in both n-mitotic and c-mitotic indices. The differences in results produced by the two methods of determining mitotic index depended upon dose and duration of treatment with BaP. The administration of Colcemid to acetone-treated mice increased the labeling index (number of labeled cells) and reduced the rate of DNA synthesis (low grain count per keratinocyte nucleus). After chronic application of BaP, Colcemid abrogated the increase in labeling index, but produced no additional effect on the number of grains per labeled keratinocyte. The modifying effect of Colcemid was greatest when administered during the peak of the tissue response to BaP. A number of significant changes in morphology of the skin associated with chronic exposure to BaP were attenuated by the use of Colcemid.

Differential effects of prednisolone and indomethacin on zymosan-induced inflammation in a modified murine tissue-chamber model

A tissue-chamber model of inflammation in mice has been modified and used to investigate the kinetics of zymosan-induced inflammatory mediators such as tumour necrosis factor alpha (TNF alpha), interleukin-1 beta (IL-1 beta) and prostaglandin E2 (PGE2). In addition, the influx of polymorphonuclear leukocytes (PMN) into the chamber fluid and the granuloma surrounding the chamber was measured by myeloperoxidase (MPO) activity using a new microtitre plate assay. TNF alpha and IL-1 beta reached a peak concentrations at 3 and 6 h respectively after zymosan injection. Intermediate high concentrations of IL-1 beta were observed until the end of the experiment at 72 h, but TNF alpha concentrations decreased from 24 h to biologically insignificant values. In contrast, exudate PGE2 and MPO activity increased up to 24 h after zymosan injection and remained high until 72 h. At 6 h after zymosan challenge, oral pre-treatment with prednisolone (3 to 30 mg/kg) dose-dependently reduced TNF alpha, IL-1 beta and PGE2 concentrations while indomethacin (0.3 to 3 mg/kg) significantly attenuated PGE2, slightly enhanced TNF alpha and had no effect on IL-1 beta concentrations in the exudate. Both drugs had similar potencies against exudate and tissue MPO activities. Prednisolone inhibited IL-1 beta at 72 h post-zymosan. Indomethacin was more potent than prednisolone against PGE2 (ID50 of< 0.3 versus 0.6 mg/kg). The data obtained confirm the usefulness and reliability of this model in evaluating the effects of anti-inflammatory agents on inflammatory mediators induced by zymosan.

Calcium oxalate monohydrate crystals stimulate gene expression in renal epithelial cells

Primary or secondary hyperoxaluria is associated with calcium oxalate nephrolithiasis, interstitial fibrosis and progressive renal insufficiency. Monolayer cultures of nontransformed monkey kidney epithelial cells (BSC-1 line) and calcium oxalate monohydrate (COM) crystals were used as a model system to study cell responses to crystal interactions that might occur in the nephrons of patients during periods of hyperoxaluria. To determine if COM crystals signal a change in gene expression, Northern blots were prepared from total renal cellular RNA after the cells were exposed to crystals. The immediate early genes c-myc, EGR-1, and Nur-77 were induced at one hour. At two to six hours stimulated expression of the genes encoding plasminogen activator inhibitor (PAI-1) and platelet-derived growth factor (PDGF)-A chain was detected, but constitutive expression of urokinase-type plasminogen activator (u-PA) was not altered. Expression of connective tissue growth factor (CTGF) was induced at one hour and persisted up to 24 hours. The stimulation of gene expression by COM crystals was relatively crystal- and renal cell-type specific. Thus the interaction of kidney epithelial cells with COM crystals alters expression of genes that encode three classes of proteins: transcriptional activators, a regulator of extracellular matrix (ECM), and growth factors. Activation of PAI-1 gene expression without a change in u-PA favors accumulation of ECM proteins, as does increased expression of PDGF and CTGF which can also stimulate fibroblast proliferation in a paracrine manner. These results suggest that COM crystal-mediated stimulation of specific genes in renal tubular cells may contribute to the development of interstitial fibrosis in hyperoxaluric states.

Effect of rolipram in a murine model of acute inflammation: comparison with the corticoid dexamethasone

Treatment of mice with rolipram, a phosphodiesterase type 4 inhibitor, selectively modified the acute inflammatory reaction elicited by zymosan administration in 6-day-old mouse air-pouches. Rolipram (1-10 mg kg-1, i.p.) prevented the rise of endogenous tumor necrosis factor-alpha (TNF-alpha) in the lavage fluids (approximately 60% inhibition) induced by zymosan, with no effect upon interleukin-1 alpha levels. This action was not accompanied by changes in neutrophil accumulation, but the amount of elastase released in the lavage fluids was significantly reduced (approximately 50%). Dexamethasone (1.5 mg kg-1, i.v.), used for comparative purposes, significantly reduced the release of TNF-alpha (> 50%), interleukin-1 alpha (> 70%) and cellular infiltration (approximately 50%), but had only a marginal effect on the release of elastase activity. In conclusion, in this murine model of acute inflammation induced by zymosan, rolipram inhibited the endogenous TNF-alpha production at a local site of inflammation, such as the subcutaneous air-pouch, and prevented the full activation of migrated cells.

Measurement and drug induced modulation of interleukin-1 level during zymosan peritonitis in mice

The time-course and pharmacological modulation of interleukin-1 (IL-1) production were investigated during zymosan induced peritonitis in mice. IL-1 alpha liberation was assessed by specific immunoassay (ELISA) and the IL-1 like bioactivity (sensitive to both alpha- and beta-forms of IL-1) was measured by a sensitive bioassay (D10G4.1 costimulation). I.p. injection of zymosan induced significant IL-1 release into the peritoneal exudate. The level peaked at 4 h and by 24 h dropped below the detection limit in both assays. The effects of the prototypical antiinflammatory drugs indomethacin (IND) and dexamethasone (DEX) and that of IX 207-887, a compound which has been reported to interfere primarily with IL-1 production, were also tested. DEX and IX 207-887 dose-dependently decreased the immunoassayable IL-1 alpha level and the IL-1 like bioactivity as well. However, IND had no suppressant effect. Thus, the data obtained by immunoassay and bioassay correlated well proving the suitability of zymosan peritonitis model for the examination of IL-1 production in experimental inflammation.

Measurement of interleukin-1 liberation in zymosan air-pouch exudate in mice

The aim of the present study was to examine whether interleukin-1 (IL-1) production is involved in the pathology of inflammation induced by zymosan in the air-pouch of mice. For this reason the IL-1 alpha level was determined in the air-pouch exudate by specific ELISA kit 4, 24, 48 h and 4-8 days after zymosan injection into preformed subcutaneous air-pouches in mice. Concurrently, some conventional parameters such as volume of exudate, its protein content and the total leukocyte count were also measured. The IL-1 alpha level reached its maximum 24 h after zymosan administration and remained elevated throughout the 8-day observation period. Exudation, accumulation of leukocytes and protein also were maximal on day 8. The effects of some anti-inflammatory agents have also been examined. Orally administered dexamethasone induced a dose-dependent reduction in IL-1 alpha, whereas indomethacin and IX 207-887, an IL-1-release inhibitor, failed to reduce the IL-1 alpha content in this model.

Crystal-induced neutrophil activation. IV. Specific inhibition of tyrosine phosphorylation by colchicine

We recently demonstrated that pathologically relevant inflammatory microcrystals, namely triclinic monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals, potently stimulate a characteristic protein tyrosine phosphorylation pattern in human neutrophils that differed from that observed in response to other soluble or particulate agonists. In this study, the effects of colchicine on protein tyrosine phosphorylation induced by MSU and CPPD crystals in human blood neutrophils were investigated. Immunoblot analysis with antiphosphotyrosine antibodies demonstrated that colchicine dose-dependently inhibited the tyrosine phosphorylation of all the proteins phosphorylated in response to MSU and CPPD crystals. Other microtubule-disruptive agents such as vinblastine, nocodazole, and colcemid also inhibited crystal-induced protein tyrosine phosphorylation while lumicolchicine and trimethylcolchicinic acid were without effect. Indomethacin and phenylbutazone were similarly without effect on microcrystal-induced tyrosine phosphorylation. Colchicine, as well as the other active alkaloids, failed to inhibit the protein tyrosine phosphorylation elicited by FMLP, C5a, leukotriene B4, and unopsonized zymosan. Overall, these results demonstrate that colchicine specifically and significantly inhibits the protein tyrosine phosphorylation induced by MSU and CPPD crystals and suggest that its effects are associated, at least in part, with its interaction with microtubules. Furthermore, the use of microtubule-disrupting drugs demonstrate that the mechanisms implicated in the induction of protein tyrosine phosphorylation by microcrystals differed from those involved in response to other soluble or particulate agonists.

A new assay for antiphlogistic activity: zymosan-induced mouse ear inflammation

A new model of local inflammation has been developed: intradermal zymosan-induced mouse ear edema. The symptoms of inflammation induced by injecting zymosan into one of the ears were followed up for 72 h. The ear edema and the local accumulation of polymorphonuclear leukocytes' (PMN) marker enzyme, myeloperoxidase (MPO), were determined. Edema peaked at 4-6 h, while MPO activity peaked at 24 h after zymosan application. The correlation between inflammatory response and concentration of zymosan was also tested. Of the various concentrations tested, 1% suspension has been found optimal. Anti-inflammatory drugs and mediator antagonists were examined in order to establish the selectivity and sensitivity of the assay. A glucocorticoid (dexamethasone), two cyclooxygenase inhibitors (indomethacin, piroxicam) and an interleukin-1 (IL-1) release inhibitor (IX 207-887, Sandoz) all reduced edema and MPO activity as well. However, a lipoxygenase inhibitor (phenidone), a serotonin receptor antagonist (methysergide) and H1 and H2 receptor antagonists (clemastine and cimetidine, respectively) all failed to inhibit the reaction.

Crystal-induced neutrophil activation. III. Inflammatory microcrystals induce a distinct pattern of tyrosine phosphorylation in human neutrophils

The activation of human neutrophils by monosodium urate and calcium pyrophosphate dihydrate crystals is believed to play a critical role in the pathogenesis of arthritides such as acute gout and pseudogout, respectively. In this study, we investigated the potential involvement of tyrosine phosphorylation in microcrystal-mediated activation of human neutrophils. Immunoblot analysis with antiphosphotyrosine antibodies demonstrated that triclinic monosodium urate and calcium pyrophosphate dihydrate crystals stimulated a time- and concentration-dependent tyrosine phosphorylation of at least five proteins (pp130, 118, 80, 70, and 60). While phosphoprotein (pp) 118 and pp70 were the major phosphorylated substrates, pp70 was the dominant one in reactivity with antiphosphotyrosine antibodies. When the temporal patterns, as well as the levels of tyrosine phosphorylation for both types of crystals were compared, monosodium urate crystals were found to be more potent activators than calcium pyrophosphate dihydrate crystals. The tyrosine phosphorylation patterns induced by microcrystals differed from those stimulated by other soluble (FMLP, C5a, or leukotriene B4) or particulate (unopsonized latex beads or zymosan) agonists which stimulated preferentially the tyrosine phosphorylation of pp118. The ratio of the intensities of pp118 and pp70 were specific of the stimulation with microcrystals when compared to those observed with the other soluble or particulate agonists. Colchicine, a drug used specifically in the treatment of gout and pseudogout, inhibited microcrystal-induced tyrosine phosphorylation, while beta- and gamma-lumicolchicine were without effect. On the other hand, colchicine failed to inhibit FMLP-induced tyrosine phosphorylation. Furthermore, while colchicine inhibited the activation of the NADPH oxidase by microcrystals, it, on the other hand, enhanced the production of superoxide anions by FMLP. Taken together, these results (a) demonstrate that tyrosine phosphorylation is involved in the mechanism of activation of human neutrophils induced by microcrystals; and (b) suggest, on the basis of the characteristics of the observed patterns of tyrosine phosphorylation, that this response may be specific to the microcrystals and relevant to their phlogistic properties.

Crystal-induced neutrophil activation. II. Evidence for the activation of a phosphatidylcholine-specific phospholipase D

OBJECTIVE

To investigate the involvement of phospholipase D in the signaling pathways activated by 2 pathologically relevant inflammatory microcrystals, monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD).

METHODS

Human peripheral blood neutrophils were used throughout. Phospholipase D activity was monitored by measuring 3 separate indices: 1) the mass of phosphatidic acid, 2) the levels of alkyl-phosphatidic acid, and 3) the levels of formation, in the presence of ethanol, of phosphatidylethanol. The latter 2 parameters were measured in cells labeled with 1-0-3H-alkyl-2-acetyl-sn-glycero-3-phosphocholine. The cells were stimulated with microcrystals of triclinic morphology.

RESULTS

Both MSU and CPPD crystals induced a time- and concentration-dependent accumulation of phosphatidic acid mass and elevation in levels of alkyl-phosphatidic acid and phosphatidylethanol in prelabeled cells. The activation of phospholipase D by the microcrystals was partially sensitive to colchicine and largely resistant to pertussis toxin. Inhibition of phosphatidic acid formation by wortmannin or ethanol reduced the microcrystal-stimulated production of superoxide anions.

CONCLUSION

These results indicate that microcrystals stimulate phospholipase D in human neutrophils and that at least some of the functional consequences of neutrophil-microcrystal interactions may be dependent on this biochemical pathway.