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

Anti-inflammatory effects of MerTK by inducing M2 macrophage polarization via PI3K/Akt/GSK-3β pathway in gout

Mer tyrosine kinase (MerTK) has been found to regulate the secretion of inflammatory factors and exert immunosuppressive effects, but its role in gout remains unclear. In this study, we aimed to clarify the immnue effects of MerTK in gout. MerTK in synovium or serum of gout patients was determined by immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), and real-time quantitative polymerase chain reaction (RT-qPCR). In monosodium urate (MSU)-induced gout mice, the effect of MerTK inhibitor (UNC2250) on inflammation and polarization was also assessed. After inhibition, knockdown or overexpression of MerTK, inflammatory response and polarization level in THP1-derived macrophages were evaluated by RT-qPCR and flow cytometry. Regulation of MerTK inhibitors on mitochondrial function and downstream pathway in THP1-derived macrophages were detected. MerTK in synovium and serum of gout patients were increased. MerTK inhibitor stimulated the inflammation and M1 polarization in MSU-induced gout mice. MerTK inhibition, knock-down, or overexpression affected inflammatory response, polarization and mitochondrial function in vitro in gout model. The PI3K/Akt/GSK-3β pathway was identified to reduce after MerTK inhibition and the relevant results were as expected, validated by knock-down or overexpressing MerTK. In conclusion, MerTK was detected to increase in both gout patients and model. MerTK influenced inflammatory response and polarization markers through PI3K/Akt/GSK-3β pathway. Interfering MerTK/PI3K/Akt/GSK-3β axis may provide a new therapeutic target for gout.

Deficiency of histone deacetylases 3 in macrophage alleviates monosodium urate crystals-induced gouty inflammation in mice

BACKGROUND

Gout is caused by monosodium urate (MSU) crystals deposition to trigger immune response. A recent study suggested that inhibition of Class I Histone deacetylases (HDACs) can significantly reduce MSU crystals-induced inflammation. However, which one of HDACs members in response to MSU crystals was still unknown. Here, we investigated the roles of HDAC3 in MSU crystals-induced gouty inflammation.

METHODS

Macrophage specific HDAC3 knockout (KO) mice were used to investigate inflammatory profiles of gout in mouse models in vivo, including ankle arthritis, foot pad arthritis and subcutaneous air pouch model. In the in vitro experiments, bone marrow-derived macrophages (BMDMs) from mice were treated with MSU crystals to assess cytokines, potential target gene and protein.

RESULTS

Deficiency of HDAC3 in macrophage not only reduced MSU-induced foot pad and ankle joint swelling but also decreased neutrophils trafficking and IL-1β release in air pouch models. In addition, the levels of inflammatory genes related to TLR2/4/NF-κB/IL-6/STAT3 signaling pathway were significantly decreased in BMDMs from HDAC3 KO mice after MSU treatment. Moreover, RGFP966, selective inhibitor of HDAC3, inhibited IL-6 and TNF-α production in BMDMs treated with MSU crystals. Besides, HDAC3 deficiency shifted gene expression from pro-inflammatory macrophage (M1) to anti-inflammatory macrophage (M2) in BMDMs after MSU challenge.

CONCLUSIONS

Deficiency of HDAC3 in macrophage alleviates MSU crystals-induced gouty inflammation through inhibition of TLR2/4 driven IL-6/STAT3 signaling pathway, suggesting that HDAC3 could contribute to a potential therapeutic target of gout.

Comparative studies of xanthine oxidase inhibitors viz. allopurinol and febuxostat against induced hyperuricaemia in a poultry model

In this study, an attempt was made to evaluate the relative efficacy of two important anti-gout agents, viz. allopurinol and febuxostat, in the control of hyperuricaemia/gout using a poultry model. A 21-day study was conducted on 48 Vencobb-400 broiler chicks randomly divided into four groups. In one group hyperuricaemia/gout was induced by the oral administration of diclofenac (group D); in two other groups the ameliorative effect of the two drugs under study was investigated by providing both simultaneously, i.e. diclofenac and allopurinol (group DA), diclofenac and febuxostat (group DF); and the fourth group was kept un-induced and untreated as a control (group C). Both allopurinol and febuxostat inhibit xanthine oxidase enzymes, thereby reducing the production of uric acid. The birds kept on diclofenac alone exhibited the highest level of hyperuricaemia, clinical signs of gout, and overt adverse changes in the visceral organs, whereas these changes were lesser in allopurinol- and febuxostat-treated groups. Furthermore, haematological, biochemical, patho-morphological, and ultra-structural studies using transmission electron microscopy were carried out to evaluate the pathology and, thus, the ameliorative effect of allopurinol and febuxostat. The findings proved that allopurinol and febuxostat carry definite ameliorative potential as anti-hyperuricemic and anti-gout agents in poultry, which was better expressed by febuxostat compared to allopurinol.

Discovery and Characterization of Moracin C as an Anti-Gouty Arthritis/Hyperuricemia Candidate by Docking-Based Virtual Screening and Pharmacological Evaluation

In the present study, a natural product database of compounds associated with herbs traditionally verified to treat gout/hyperuricemia/arthritis was constructed. 3D-shape and docking-based virtual screening was conducted. To identify potential xanthine oxidase (XOD) inhibitors in the database, eight compounds with commercial availability were identified as high 3D-shape similarity with febuxostat (1), a known XOD inhibitor. Docking was used to further predict the possible interactions between XOD and these compounds. Moracin C (2), moracin D (3), and isoformononetin (8) exhibited higher docking scores and binding energies than other compounds. In vitro, 2 inhibited XOD with an IC50 value of 0.25 ± 0.14 μM, which is similar to that of 1 (0.16 ± 0.08 μM). In a hyperuricemic mouse model, 5-20 mg/kg 2 exhibited satisfying urate-lowering and XOD inhibitory effects. Compound 2 also exhibited antiarthritis activities. In RAW264.7 cells, 2 at 1-10 μM inhibited the expression of IL-1β and TNF-α induced by MSU. In an acute gouty arthritis model in SD rats, 5-20 mg/kg 2 significantly alleviated the toe swelling, inflammatory response, and dysfunction disorder caused by monosodium urate (MSU). Compound 2 inhibited serum IL-1β and TNF-α cytokines as well as reduced the expression of the NLRP3/ASC/caspase-1 inflammasome in joints. In summary, 2 was an effective compound for the treatment of hyperuricemia/gouty arthritis.

The landscape of pathophysiology guided therapeutic strategies for gout treatment

INTRODUCTION

Gout is a common autoinflammatory disease caused by hyperuricemia with acute and/or chronic inflammation as well as tissue damage. Currently, urate-lowering therapy (ULT) and anti-inflammatory therapy are used as first-line strategies for gout treatment. However, traditional drugs for gout treatment exhibit some unexpected side effects and are not suitable for certain patients due to their comorbidity with other chronic disease.

AREAS COVERED

In this review, we described the pathophysiology of hyperuricemia and monosodium urate (MSU) crystal induced inflammatory response during gout development in depth and comprehensively summarized the advances in the investigation of promising ULT drugs as well as anti-inflammatory drugs that might be safer and more effective for gout treatment.

EXPERT OPINION

New drugs that are developed based on these molecular mechanisms exhibited great efficacy on reduction of disease burden both in vitro and in vivo, implying their potential for clinical application. Moreover, hyperthermia also showed regulation effect on MSU crystals formation and the signaling pathways involved in inflammation.

MSC therapy ameliorates experimental gouty arthritis hinting an early COX-2 induction

Objective

The specific effect of Adipose-Derived Mesenchymal Stem Cells (Ad-MSC) on acute joint inflammation, where the response mostly depends on innate immunity activation, remains elusive. The pathogenesis of gouty arthritis, characterized by the deposition of monosodium urate (MSU) crystals in the joints, associated to acute flares, has been associated to NLRP3 inflammasome activation and subsequent amplification of the inflammatory response. Our aim was to study the effect of human Ad-MSC administration in the clinical inflammatory response of rabbits after MSU injection, and the molecular mechanisms involved.

Methods

Ad-MSC were administered by intraarterial route shortly after intraarticular MSU crystal injections. Joint and systemic inflammation was sequentially studied, and the mechanisms involved in NLRP3 inflammasome activation, and the synthesis of inflammatory mediators were assessed in the synovial membranes 72h after insult. Ad-MSC and THP-1-derived macrophages stimulated with MSU were co-cultured in transwell system.

Results

A single systemic dose of Ad-MSC accelerated the resolution of local and systemic inflammatory response. In the synovial membrane, Ad-MSC promoted alternatively M2 macrophage presence, inhibiting NLRP3 inflammasome and inducing the production of anti-inflammatory cytokines, such as IL-10 or TGF-β, and decreasing nuclear factor-κB activity. Ad-MSC induced a net anti-inflammatory balance in MSU-stimulated THP-1 cells, with a higher increase in IL-10 and IDO expression than that observed for IL-1β and TNF.

Conclusion

Our in vivo and in vitro results showed that a single systemic dose of Ad-MSC decrease the intensity and duration of the inflammatory response by an early local COX-2 upregulation and PGE2 release. Ad-MSCs suppressed NF-kB activity, NLRP3 inflammasome, and promoted the presence of M2 alternative macrophages in the synovium. Therefore, this therapeutic approach could be considered as a pharmacological alternative in patients with comorbidities that preclude conventional treatment.

Targeting different phenotypes of macrophages: A potential strategy for natural products to treat inflammatory bone and joint diseases

BACKGROUND

Macrophages, a key class of immune cells, have a dual role in inflammatory responses, switching between anti-inflammatory M2 and pro-inflammatory M1 subtypes depending on the specific environment. Greater numbers of M1 macrophages correlate with increased production of inflammatory chemicals, decreased osteogenic potential, and eventually bone and joint disorders. Therefore, reversing M1 macrophages polarization is advantageous for lowering inflammatory factors. To better treat inflammatory bone disorders in the future, it may be helpful to gain insight into the specific mechanisms and natural products that modulate macrophage polarization.

OBJECTIVE

This review examines the impact of programmed cell death and different cells in the bone microenvironment on macrophage polarization, as well as the effects of natural products on the various phenotypes of macrophages, in order to suggest some possibilities for the treatment of inflammatory osteoarthritic disorders.

METHODS

Using 'macrophage polarization,' 'M1 macrophage' 'M2 macrophage' 'osteoporosis,' 'osteonecrosis of femoral head,' 'osteolysis,' 'gouty arthritis,' 'collagen-induced arthritis,' 'freund's adjuvant-induced arthritis,' 'adjuvant arthritis,' and 'rheumatoid arthritis' as search terms, the relevant literature was searched using the PubMed, the Cochrane Library and Web of Science databases.

RESULTS

Targeting macrophages through different signaling pathways has become a key mechanism for the treatment of inflammatory bone and joint diseases, including HIF-1α, NF-κB, AKT/mTOR, JAK1/2-STAT1, NF-κB, JNK, ERK, p-38α/β, p38/MAPK, PI3K/AKT, AMPK, AMPK/Sirt1, STAT TLR4/NF-κB, TLR4/NLRP3, NAMPT pathway, as well as the programmed cell death autophagy, pyroptosis and ERS.

CONCLUSION

As a result of a search of databases, we have summarized the available experimental and clinical evidence supporting herbal products as potential treatment agents for inflammatory osteoarthropathy. In this paper, we outline the various modulatory effects of natural substances targeting macrophages in various diseases, which may provide insight into drug options and directions for future clinical trials. In spite of this, more mechanistic studies on natural substances, as well as pharmacological, toxicological, and clinical studies are required.

Damage-mediated macrophage polarization in sterile inflammation

Most of the leading causes of death, such as cardiovascular diseases, cancer, dementia, neurodegenerative diseases, and many more, are associated with sterile inflammation, either as a cause or a consequence of these conditions. The ability to control the progression of inflammation toward tissue resolution before it becomes chronic holds significant clinical potential. During sterile inflammation, the initiation of inflammation occurs through damage-associated molecular patterns (DAMPs) in the absence of pathogen-associated molecules. Macrophages, which are primarily localized in the tissue, play a pivotal role in sensing DAMPs. Furthermore, macrophages can also detect and respond to resolution-associated molecular patterns (RAMPs) and specific pro-resolving mediators (SPMs) during sterile inflammation. Macrophages, being highly adaptable cells, are particularly influenced by changes in the microenvironment. In response to the tissue environment, monocytes, pro-inflammatory macrophages, and pro-resolution macrophages can modulate their differentiation state. Ultimately, DAMP and RAMP-primed macrophages, depending on the predominant subpopulation, regulate the balance between inflammatory and resolving processes. While sterile injury and pathogen-induced reactions may have distinct effects on macrophages, most studies have focused on macrophage responses induced by pathogens. In this review, which emphasizes available human data, we illustrate how macrophages sense these mediators by examining the expression of receptors for DAMPs, RAMPs, and SPMs. We also delve into the signaling pathways induced by DAMPs, RAMPs, and SPMs, which primarily contribute to the regulation of macrophage differentiation from a pro-inflammatory to a pro-resolution phenotype. Understanding the regulatory mechanisms behind the transition between macrophage subtypes can offer insights into manipulating the transition from inflammation to resolution in sterile inflammatory diseases.

A review on gout: Looking back and looking ahead

Gout is a metabolic disease caused by the deposition of monosodium urate (MSU) crystals inside joints, which leads to inflammation and tissue damage. Increased concentration of serum urate is an essential step in the development of gout. Serum urate is regulated by urate transporters in the kidney and intestine, especially GLUT9 (SLC2A9), URAT1 (SLC22A12) and ABCG. Activation of NLRP3 inflammasome bodies and subsequent release of IL-1β by monosodium urate crystals induce the crescendo of acute gouty arthritis, while neutrophil extracellular traps (NETs) are considered to drive the self-resolving of gout within a few days. If untreated, acute gout may eventually develop into chronic tophaceous gout characterized by tophi, chronic gouty synovitis, and structural joint damage, leading the crushing burden of treatment. Although the research on the pathological mechanism of gout has been gradually deepened in recent years, many clinical manifestations of gout are still unable to be fully elucidated. Here, we reviewed the molecular pathological mechanism behind various clinical manifestations of gout, with a view to making contributions to further understanding and treatment.

Gouty arthritis involves impairment of autophagic degradation via cathepsin D inactivation-mediated lysosomal dysfunction that promotes apoptosis in macrophages

This study examined autophagy-lysosome pathway (ALP) perturbations in synovial monocytes/macrophages from patients with gouty arthritis (GA) and the associations of ALP perturbations with cell death. Synovial fluid mononuclear cells (SFMCs) and synovial tissues (STs) from patients with GA, as well as monosodium urate (MSU) crystal-exposed macrophages, underwent immunoblotting, quantitative polymerase chain reaction, and immunofluorescence analyses of markers linked to the ALP (microtubule-associated protein 1 light chain 3B [LC3B], p62, cathepsin D [CTSD], and lysosome-associated membrane protein 2 [LAMP2]) and cell death (caspase-3). GA STs underwent immunohistochemistry and immunofluorescence analyses to determine the distributions of LC3B-positive autophagosomes and macrophages. GA SFMCs and STs exhibited impaired autophagic degradation, indicated by elevated levels of LC3B and p62, along with CTSD upregulation and caspase-3 activation. Macrophages from GA STs exhibited significant accumulation of LC3B-positive autophagosomes. The temporal effects of MSU crystals on the ALP and the associations of these effects with cell death were investigated using a macrophage model of GA. MSU crystal-exposed macrophages exhibited early (2 h) autophagosome formation but later (6-24 h) autophagic flux impairment, demonstrated by p62 accumulation, lysosomal inhibitor failure to increase LC3B accumulation, and LC3B colocalization with p62. These macrophages exhibited autophagic flux impairment because of CTSD inactivation-mediated lysosomal dysfunction, which caused immature CTSD to accumulate within damaged LAMP2-positive lysosomes. This accumulation coincided with caspase-3-dependent cell death (24 h) that was unaffected by CTSD inhibition. These findings indicate that GA involves MSU crystal-induced impairment of autophagic degradation via CTSD inactivation-mediated lysosomal dysfunction, which promotes apoptosis in macrophages.

Obesity in pregnancy is associated with macrophage influx and an upregulated GRO-alpha and IL-6 expression in the decidua

About one third of all reproductive-aged women are affected by obesity. Maternal obesity is linked to an adverse outcome for both mother and child. The expression of the pro-inflammatory IL-6 and GRO-alpha as well as the infiltration of macrophages in the placenta of obese, non-diabetic pregnancies was examined by immunohistochemistry in comparison to the placenta of normal weight women. In obese pregnancies the influx of macrophages was significantly increased (p = 0.012). The protein expression of IL-6 and GRO-alpha was significantly elevated (p = 0.036 and p < 0.001, respectively) in the decidua of adipose females.

Protein phosphatase 2A regulates xanthine oxidase-derived ROS production in macrophages and influx of inflammatory monocytes in a murine gout model

Background: Gout is a common arthritis, due to deposition of monosodium urate (MSU) crystals which results in IL-1β secretion by tissue-resident macrophages. Xanthine oxidase (XO) catalyzes uric acid (UA) production and in the process, reactive oxygen species (ROS) are generated which contributes to NLRP3 inflammasome activation. Protein phosphatase 2A (PP2A) may be involved in regulating inflammatory pathways in macrophages. The objective of this study was to investigate whether PP2A regulates gout inflammation, mediated by XO activity modulation. We studied UA and ROS generations in MSU stimulated murine bone marrow derived macrophages (BMDMs) in response to fingolimod phosphate, a PP2A activator, and compared its anti-inflammatory efficacy to that of an XO inhibitor, febuxostat. Methods: BMDMs were stimulated with MSU, GM-CSF/IL-1β or nigericin ± fingolimod (2.5 μM) or febuxostat (200 μM) and UA levels, ROS, XO, and PP2A activities, Xdh (XO) expression and secreted IL-1β levels were determined. PP2A activity and IL-1β in MSU stimulated BMDMs ± N-acetylcysteine (NAC) (10 μM) ± okadaic acid (a PP2A inhibitor) were also determined. M1 polarization of BMDMs in response to MSU ± fingolimod treatment was assessed by a combination of iNOS expression and multiplex cytokine assay. The in vivo efficacy of fingolimod was assessed in a murine peritoneal model of acute gout where peritoneal lavages were studied for pro-inflammatory classical monocytes (CMs), anti-inflammatory nonclassical monocytes (NCMs) and neutrophils by flow cytometry and IL-1β by ELISA. Results: Fingolimod reduced intracellular and secreted UA levels (p < 0.05), Xdh expression (p < 0.001), XO activity (p < 0.001), ROS generation (p < 0.0001) and IL-1β secretion (p < 0.0001), whereas febuxostat enhanced PP2A activity (p < 0.05). NAC treatment enhanced PP2A activity and reduced XO activity and PP2A restoration mediated NAC's efficacy as co-treatment with okadaic acid increased IL-1β secretion (p < 0.05). Nigericin activated caspase-1 and reduced PP2A activity (p < 0.001) and fingolimod reduced caspase-1 activity in BMDMs (p < 0.001). Fingolimod reduced iNOS expression (p < 0.0001) and secretion of IL-6 and TNF-α (p < 0.05). Fingolimod reduced CMs (p < 0.0001), neutrophil (p < 0.001) and IL-1β (p < 0.05) lavage levels while increasing NCMs (p < 0.001). Conclusion: Macrophage PP2A is inactivated in acute gout by ROS and a PP2A activator exhibited a broad anti-inflammatory effect in acute gout in vitro and in vivo.

Distinct macrophage polarization in acute and chronic gout

Macrophage polarization mediates the development of inflammatory diseases. However, the polarization status at various stages of gout is not fully understood. Our study aimed to define the evolution of macrophage polarization in acute and chronic gout. Normal human synovium and synovium with tophi were collected for immunofluorescence (IF). Rat gouty joints were collected for joint thickness assessment and pathological evaluation. Tissue mRNA expression of inducible nitric oxide synthase (iNOS) and arginase-1 (Arg-1) were evaluated. Mouse peritoneal macrophages and THP-1 derived macrophages were stimulated by monosodium urate (MSU) crystals and were collected for detection of interleukin (IL) -1β and IL-37 levels and iNOS/Arg-1 ratio. Arg-1 and IL-37 were highly expressed in normal synovium and synovium with tophi. In rat gouty joints, the inflammatory cell counts and ankle thickness began to increase at 2 h, peaked at 24 h, and was decreased spontaneously. An increase in macrophages preceded the neutrophils infiltration. Infiltration of M1 was positively related with the severity of arthritis. M2 appeared in an early stage (at 2 h) of inflammation. The number of M1 macrophages was comparable to that of M2 from 2 to 12 h and exceeded M2 number at 18 h and 24 h. The ratios of M2/M1 reversed at 48 h and remained reversed until 120 h. In mice gouty joints, iNOS/Arg-1 mRNA ratio was significantly higher than the that in control group at 8 h. The proportion of neutrophils and M1-macrophages reached peak at 4 h in mice model with peritoneal gout. Concentration of IL-1β and ratio of iNOS/Arg-1 were increased at 6 h, peaked at 48 h, and were then decreased at 72 h in vitro, while the concentration of IL-37 peaked at 2 h and then decreased. In summary, altered macrophage polarization was observed in various stages of gouty inflammation. Macrophages in acute gout were polarized into M1 at early stage and into M2 at later stage while the macrophages in chronic gout mainly were only polarized towards M2. The number of M1 rose with the progression of inflammation. Early increase of M2 was observed, which might be generated directly from M0.

Recent Insights Into the Role of Macrophages in Acute Gout

Gout is a common type of inflammatory arthritis characterized by the presence of monosodium urate crystals (MSU) in the joints. Macrophages are believed to be involved in gout flares. It has long been recognized that resident macrophage and monocyte derived macrophages are distinct subsets and there have been attempts to investigate their roles in acute gout, respectively. Previous studies revealed that resident macrophages initiate and drive the inflammation, while monocyte derived macrophages differentiated into M1-like macrophages in response to MSU crystals. With the advancement of technologies, subpopulations of synovial resident macrophages have been defined with the characteristics more accurately described. Resident macrophages in the synovial lining layer showed an anti-inflammatory effect in rheumatoid arthritis, but specific Trpv4 depletion of them reduced MSU crystals induced murine arthritis. CD14+ monocytes in the synovial fluid from patients with gout exhibit phenotypes of anti-inflammatory as well as pro-inflammatory characteristics. Here, we review the main aspects of macrophages in the initiation and resolution of acute gout and try to clarify the specific role of each subpopulation. Building a reliable diagram of the effect of monocytes and macrophages during MSU crystals induced arthritis will bring us closer to targeting macrophages for improving the management of gout.

Recombinant Human Proteoglycan 4 Regulates Phagocytic Activation of Monocytes and Reduces IL-1β Secretion by Urate Crystal Stimulated Gout PBMCs

Objectives

To compare phagocytic activities of monocytes in peripheral blood mononuclear cells (PBMCs) from acute gout patients and normal subjects, examine monosodium urate monohydrate (MSU) crystal-induced IL-1β secretion ± recombinant human proteoglycan 4 (rhPRG4) or interleukin-1 receptor antagonist (IL-1RA), and study the anti-inflammatory mechanism of rhPRG4 in MSU stimulated monocytes.

Methods

Acute gout PBMCs were collected from patients in the Emergency Department and normal PBMCs were obtained from a commercial source. Monocytes in PBMCs were identified by flow cytometry. PBMCs were primed with Pam3CSK4 (1μg/mL) for 24h and phagocytic activation of monocytes was determined using fluorescently labeled latex beads. MSU (200μg/mL) stimulated IL-1β secretion was determined by ELISA. Reactive oxygen species (ROS) generation in monocytes was determined fluorometrically. PBMCs were incubated with IL-1RA (250ng/mL) or rhPRG4 (200μg/mL) and bead phagocytosis by monocytes was determined. THP-1 monocytes were treated with MSU crystals ± rhPRG4 and cellular levels of NLRP3 protein, pro-IL-1β, secreted IL-1β, and activities of caspase-1 and protein phosphatase-2A (PP2A) were quantified. The peritoneal influx of inflammatory and anti-inflammatory monocytes and neutrophils in Prg4 deficient mice was studied and the impact of rhPRG4 on immune cell trafficking was assessed.

Results

Enhanced phagocytic activation of gout monocytes under basal conditions (p<0.001) was associated with ROS generation and MSU stimulated IL-1β secretion (p<0.05). rhPRG4 reduced bead phagocytosis by normal and gout monocytes compared to IL-1RA and both treatments were efficacious in reducing IL-1β secretion (p<0.05). rhPRG4 reduced pro-IL-1β content, caspase-1 activity, conversion of pro-IL-1β to mature IL-1β and restored PP2A activity in monocytes (p<0.05). PP2A inhibition reversed rhPRG4’s effects on pro-IL-1β and mature IL-1β in MSU stimulated monocytes. Neutrophils accumulated in peritoneal cavities of Prg4 deficient mice (p<0.01) and rhPRG4 treatment reduced neutrophil accumulation and enhanced anti-inflammatory monocyte influx (p<0.05).

Conclusions

MSU phagocytosis was higher in gout monocytes resulting in higher ROS and IL-1β secretion. rhPRG4 reduced monocyte phagocytic activation to a greater extent than IL-1RA and reduced IL-1β secretion. The anti-inflammatory activity of rhPRG4 in monocytes is partially mediated by PP2A, and in vivo, PRG4 plays a role in regulating the trafficking of immune cells into the site of a gout flare.

The Anti-Inflammatory and Uric Acid Lowering Effects of Si-Miao-San on Gout

Background

Si-Miao-San (SMS) is a well-known traditional Chinese medicine. This study aims to evaluate the anti-inflammatory effects of SMS on gouty arthritis and its potential mechanism of action.

Methods

The effects and mechanism of SMS were evaluated in monosodium urate (MSU)-treated mice or macrophages. The expression of cytokines and PI3K/Akt was analyzed using real-time PCR and Western blotting analyses. Macrophage polarization was assessed with immunofluorescence assays, real-time PCR, and Western blotting. Mass spectrometry was used to screen the active ingredients of SMS.

Results

Pretreatment with SMS ameliorated MSU-induced acute gouty arthritis in mice with increased PI3K/Akt activation and M2 macrophage polarization in the joint tissues. In vitro, SMS treatment significantly inhibited MSU-triggered inflammatory response, increased p-Akt and Arg-1 expression in macrophages, and promoted M2 macrophage polarization. These effects of SMS were inhibited when PI3K/Akt activation was blocked by LY294002 in the macrophages. Moreover, SMS significantly reduced serum uric acid levels in the hyperuricemia mice. Using mass spectrometry, the plant hormones ecdysone and estrone were detected as the potentially effective ingredients of SMS.

Conclusion

SMS ameliorated MSU-induced gouty arthritis and inhibited hyperuricemia. The anti-inflammatory mechanism of SMS may exert anti-inflammatory effects by promoting M2 polarization via PI3K/Akt signaling. Ecdysone and estrone might be the potentially effective ingredients of SMS. This research may provide evidence for the application of SMS in the treatment of gout.

The protective effects of S14G-humanin (HNG) against mono-sodium urate (MSU) crystals- induced gouty arthritis

Gout is a common and complex form of arthritis that has brought great inconveniences to the normal lives of patients. It is reported that oxidative stress and nod-like receptor family protein 3 (NLRP3) inflammasome-mediated inflammatory reactions are involved in the pathogenesis of gout arthritis. S14G-humanin (S14G-HNG) is a modified peptide of HNG with higher inhibitory activity on the accumulation and deposition of Aβ. Recently, S14G-HNG has been reported to exert great anti-inflammatory effects. The present study proposed to explore the possible therapeutic property of S14G-HNG against gout arthritis. An animal model was established by stimulation with mono-sodium urate (MSU) crystals, followed by treatment with colchicine and S14G-HNG, respectively. The elevated Gait score promoted synovitis score and activated myeloperoxidase (MPO) observed in MSU crystals-treated mice were significantly reversed by colchicine and S14G-HNG. Bone marrow-derived macrophages (BMDMs) were isolated from mice and stimulated with MSU crystals, followed by being treated with 25 and 50 μM S14G-HNG. The increased mitochondrial reactive oxygen species (ROS) and Malondialdehyde (MDA) levels, upregulated NADPH oxidase-4 (NOX-4), activated NLRP3 inflammasome, and elevated production of inflammatory factors in MSU crystals-treated BMDMs were dramatically reversed by S14G-HNG, accompanied by the upregulation of sirtuin type-1 (SIRT1). Lastly, the protective effects of S14G-HNG against MSU crystals-induced NLRP3 inflammasome activation were significantly abolished by the knockdown of SIRT1. In conclusion, our data reveal that S14G-HNG could possess potential benefits against MSU crystals-induced gout arthritis, with colchicine displaying a better effect.

Immune Dysregulation in IgG4-Related Disease

Immunoglobin G₄-related disease (IgG₄-RD) is one of the newly discovered autoimmune diseases characterized by elevated serum IgG₄ concentrations and multi-organ fibrosis. Despite considerable research and recent advances in the identification of underlying immunological processes, the etiology of this disease is still not clear. Adaptive immune cells, including different types of T and B cells, and cytokines secreted by these cells play a vital role in the pathogenesis of IgG₄-RD. Antigen-presenting cells are stimulated by pathogens and, thus, contribute to the activation of naïve T cells and differentiation of different T cell subtypes, including helper T cells (Th1 and Th2), regulatory T cells, and T follicular helper cells. B cells are activated and transformed to plasma cells by T cell-secreted cytokines. Moreover, macrophages, and some important factors (TGF-β, etc.) promote target organ fibrosis. Understanding the role of these cells and cytokines implicated in the pathogenesis of IgG₄-RD will aid in developing strategies for future disease treatment and drug development. Here, we review the most recent insights on IgG₄-RD, focusing on immune dysregulation involved in the pathogenesis of this autoimmune condition.

Minimally Invasive Embedding of Saturated MSU Induces Persistent Gouty Arthritis in Modified Rat Model

Introduction

Animal models are valid for in vivo research on the pathophysiological process and drug screening of gout arthritis. Intra-articular injection of monosodium urate (MSU) is the most common method, while stable MSU deposition enveloped by inflammatory cells was rarely reported.

Objective

To develop a modified gouty arthritis rat model characterized by intra-articular MSU deposition and continuous joint pain with a minimally invasive method.

Method

A total of twenty-four rats were randomly allocated into six groups. Three intervention groups of rats received intra-articular MSU embedment. Sham groups received pseudosurgeries with equal normal saline (NS). Gross parameters and pathological features of synovium harvested from anterior capsule were estimated. Mechanical pain threshold tests were conducted over a 96-hour period postoperatively. Moreover, quantitative immunofluorescence was conducted to assess tissue inflammation.

Result

After MSU embedding, rats got more persistent arthritic symptoms as well as tissue MSU deposition. More significant synovial swelling was detected in the MSU group compared to sham groups (P < 0.025). Behavioral tests showed that the embedding of MSU resulted in prolonged mechanical hyperalgesia during 2 hours to 96 hours postoperatively (P < 0.05). MSU depositions enveloped by inflammatory cells that express IL-1β and TNF-α were detected in embedding groups. Quantitative immunofluorescence suggested that the frequencies of MSU interventions upregulated expression of proinflammatory factors including IL-1β and TNF-α (P < 0.05).

Conclusion

A minimally invasive method was developed to establish modified rat model of intra-articular MSU deposition. This model was proved to be a simple reproducible method to mimic the pathological characteristics of persistent gouty arthritis.

Neutrophil extracellular trap clearance by synovial macrophages in gout

Background

Monosodium urate (MSU) crystals, i.e., the central etiological factors in gouty arthritis, induce the formation of neutrophil extracellular traps (NETs). We investigated whether synovial macrophages could clear NETs as a self-resolution mechanism in acute gouty arthritis.

Methods

Synovial fluid mononuclear cells (SFMCs) were incubated with NETs induced by MSU crystals. NET engulfment was determined based on neutrophil elastase (NE), myeloperoxidase (MPO), and SYTOX Green signals within synovial fluid CD14⁺ cells. In addition, the correlations between CD14⁺ cells, MPO-dsDNA complexes, and expression of pro- and anti-inflammatory cytokines were analyzed in the synovial fluid CD14⁺ macrophages of patients with gouty arthritis.

Results

Synovial fluid CD14⁺ macrophages significantly engulfed the MSU crystal-induced NETs, as evidenced by the alteration in SYTOX Green intensity or the presence of NE and MPO in the cytoplasm of CD14⁺ cells. The proportion of CD14⁺ macrophages was significantly and inversely correlated with levels of MPO-dsDNA complex in the synovial fluid of gout patients. Synovial fluid CD14⁺ macrophages cultured with NETs did not show a significant induction in pro- and anti-inflammatory cytokines.

Conclusion

Synovial fluid macrophages may play an important role in the resolution of MSU crystal-induced gouty inflammation by clearing NETs without causing any significant immunological response.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02472-4.

Cichoric Acid Ameliorates Monosodium Urate-Induced Inflammatory Response by Reducing NLRP3 Inflammasome Activation via Inhibition of NF-kB Signaling Pathway

Gouty arthritis is characterized by the deposition of monosodium urate (MSU) within synovial joints and tissues due to increased urate concentrations. Here, we elucidated the role of the natural compound cichoric acid (CA) on the MSU crystal-stimulated inflammatory response. The THP-1-derived macrophages (THP-Ms) were pretreated with CA and then stimulated with MSU suspensions. The protein levels of p65 and IκBα, the activation of the NF-κB signaling pathway by measuring the expression of its downstream inflammatory cytokines, and the activity of NLRP3 inflammasome were measured by western blotting and ELISA. CA treatment markedly inhibited the degradation of IκBα and the activation of NF-κB signaling pathway and reduced the levels of its downstream inflammatory genes such as IL-1β, TNF-α, COX-2, and PGE2 in the MSU-stimulated THP-M cells. Therefore, we infer that CA effectively alleviated MSU-induced inflammation by suppressing the degradation of IκBα, thereby reducing the activation of the NF-κB signaling pathway and the NLRP3 inflammasome. These results suggest that CA could be a novel therapeutic strategy in averting acute episodes of gout.

Fingolimod Phosphate (FTY720-P) Activates Protein Phosphatase 2A in Human Monocytes and Inhibits Monosodium Urate Crystal-Induced Interleukin-1β Production

Gout is a chronic inflammatory arthritis caused by monosodium urate monohydrate (MSU) crystal deposits in joints of lower limbs. Phagocytic uptake of MSU crystals by joint-resident macrophages and recruited circulating monocytes results in IL-1β expression and production. Current acute gout treatments have serious toxicities and suffer suboptimal clinical outcomes. Protein phosphatase 2A (PP2A) plays an important role in regulating signaling pathways relevant to inflammation. We hypothesized that innate immune danger signals, e.g., lipopolysaccharide (LPS) and soluble uric acid (sUA), prime human monocytes toward MSU crystal phagocytosis and that increased IL-1β production mediated by a reduction in PP2A activity and restoring PP2A activity exerts an anti-inflammatory effect in this setting. Priming monocytes with LPS + sUA increased cytosolic pro-IL-1β and mature IL-1β and enhanced MSU crystal phagocytosis and its downstream IL-1β expression (P < 0.001). A combination of LPS + sUA priming and MSU crystals reduced PP2A activity in monocytes by 60% (P = 0.013). PP2A catalytic subunit gene knockdown reduced PP2A activity and exacerbated MSU crystal-induced IL-1β expression and secretion (P < 0.0001). Fingolimod (FTY720) and its active metabolite, fingolimod phosphate (FTY720-P), were evaluated for their ability to activate PP2A in human monocytes over 24 hours. FTY720 and FTY720-P activated PP2A to a similar extent, and maximal enzyme activity occurred at 24 hours for FTY720 and at 6 hours for FTY720-P. FTY720-P (2.5 μM) reduced pro-IL-1β production and IL-1β secretion in primed and MSU crystal-stimulated monocytes (P < 0.0001) without changing the magnitude of crystal phagocytosis. We conclude that PP2A is a promising new target in acute gout. SIGNIFICANCE STATEMENT: The activity of protein phosphatase 2A (PP2A) is implicated in the enhanced expression and production of IL-1β by human monocytes in response to priming with soluble uric acid and lipopolysaccharide and phagocytosis of monosodium urate monohydrate (MSU) crystals. Fingolimod phosphate activates PP2A in human monocytes and reduces cytosolic pro-IL-1β content and its conversion to biologically active IL-1β in human monocytes exposed to MSU crystals.

Only Hyperuricemia with Crystalluria, but not Asymptomatic Hyperuricemia, Drives Progression of Chronic Kidney Disease

BACKGROUND

The roles of asymptomatic hyperuricemia or uric acid (UA) crystals in CKD progression are unknown. Hypotheses to explain links between UA deposition and progression of CKD include that (1) asymptomatic hyperuricemia does not promote CKD progression unless UA crystallizes in the kidney; (2) UA crystal granulomas may form due to pre-existing CKD; and (3) proinflammatory granuloma-related M1-like macrophages may drive UA crystal-induced CKD progression.

METHODS

MALDI-FTICR mass spectrometry, immunohistochemistry, 3D confocal microscopy, and flow cytometry were used to characterize a novel mouse model of hyperuricemia and chronic UA crystal nephropathy with granulomatous nephritis. Interventional studies probed the role of crystal-induced inflammation and macrophages in the pathology of progressive CKD.

RESULTS

Asymptomatic hyperuricemia alone did not cause CKD or drive the progression of aristolochic acid I-induced CKD. Only hyperuricemia with UA crystalluria due to urinary acidification caused tubular obstruction, inflammation, and interstitial fibrosis. UA crystal granulomas surrounded by proinflammatory M1-like macrophages developed late in this process of chronic UA crystal nephropathy and contributed to the progression of pre-existing CKD. Suppressing M1-like macrophages with adenosine attenuated granulomatous nephritis and the progressive decline in GFR. In contrast, inhibiting the JAK/STAT inflammatory pathway with tofacitinib was not renoprotective.

CONCLUSIONS

Asymptomatic hyperuricemia does not affect CKD progression unless UA crystallizes in the kidney. UA crystal granulomas develop late in chronic UA crystal nephropathy and contribute to CKD progression because UA crystals trigger M1-like macrophage-related interstitial inflammation and fibrosis. Targeting proinflammatory macrophages, but not JAK/STAT signaling, can attenuate granulomatous interstitial nephritis.

Gout: a disease involved with complicated immunoinflammatory responses: a narrative review

Gout is a disease with acute and/or chronic inflammation and tissue damage induced by the precipitation of monosodium urate crystal (MSU) crystals in bone joints, kidneys, and subcutaneous sites. In recent years, with the continuous research on gout animal models and patient clinical investigations, the mechanism of inflammation activation of gout has been further discovered. Studies have shown that pro-inflammatory factors such as interleukin (IL)-1β, IL-8 and IL-17, NLRP3 inflammasome, and tumor necrosis factor alpha (TNF-α), anti-inflammatory factors such as IL-10, IL-37 are all involved in the MSU-induced gout inflammatory process. And the immune cells in gout, including neutrophils, monocytes/macrophages, and lymphocytes, all play important roles in the pathogenesis of gout. In this review, we mainly emphasize the understanding of various cytokines, inflammasome, and immune cells involved in the onset of gout, in order to provide a systematic and theoretical basis for the novel exploration of inflammatory therapeutic targets for gout.

Huzhang Tongfeng Granule Improves Monosodium Urate-Induced Inflammation of Gouty Arthritis Rat Model by Downregulation of Cyr61 and Related Cytokines

OBJECTIVE

Gouty arthritis (GA) is a noninfectious inflammatory disease characterized by self-limited and severe pain. Huzhang Tongfeng granule is one of the most effective traditional Chinese medicines in the treatment of acute GA. However, its effects on the inflammatory factors in the process of acute gout inflammation remain unknown. In the present study, we aimed to evaluate the effect of Huzhang Tongfeng granule on the expressions of Cyr61 and related inflammatory factors in both experimental gout models in vivo and in vitro.

METHODS

Huzhang Tongfeng granule was provided by the pharmaceutical preparation room of Yueyang Hospital of Integrated Traditional Chinese and Western Medicine. The expressions of Cyr61, IL-1β, TNF-α, and IL-6 in monosodium urate- (MSU-) induced rat models and fibroblast-like synoviocytes (FLSs) were determined by RT-PCR, Western blotting analysis, ELISA, immunohistochemistry, and hematoxylin and eosin staining.

RESULTS

Huzhang Tongfeng granule could downregulate the expressions of IL-1β, TNF-α, and IL-6 to some extent by inhibiting the expression of Cyr61.

CONCLUSIONS

Collectively, our findings indicated that Cyr61 was highly expressed in rat models of gout. By inhibiting the expression of Cyr61, Huzhang Tongfeng granule could partially attenuate the inflammation induced by MSU crystal.

Total saponin of Dioscorea collettii attenuates MSU crystal‑induced inflammation via inhibiting the activation of the NALP3 inflammasome and caspase‑1 in THP‑1 macrophages

Total saponins extracted from Dioscorea collettii (TSD), extracts of the Chinese herb Dioscorea, are thought to exhibit therapeutic benefit in gouty arthritis. However, its exact mechanism remains unclear. The current study aimed to elucidate the underlying mechanisms by investigating the effects of TSD on the inflammation induced by monosodium urate (MSU) crystals in THP-1 macrophages. The viability of THP-1 macrophages was examined using the MTT assay and the levels of inflammatory cytokines, including interleukin (IL)-1β, IL-18 and tumor necrosis factor (TNF)-α, released by the cells were quantitatively measured using ELISA kits. The results revealed that the protein level of cluster of differentiation 11b increased in THP-1 cells treated with 100 ng/ml phorbol ester, suggesting that monocytic THP-1 cells were successfully differentiated into macrophages. TSD decreased the levels of inflammatory cytokines, including TNF-α, IL-18 and IL-1β, secreted by THP-1 macrophages. As the release of IL-1β and IL-18 is dependent on the NLR family pyrin domain containing 3 (NALP3) inflammasome and caspase-1, the current study investigated the effect of TSD on the aforementioned proteins. The results revealed that TSD decreased the protein levels of NALP3 and apoptosis-associated speck-like, which serve important roles in the assembly of the NALP3 inflammasome. Furthermore, NALP3 inflammasome-related proteins were also decreased by TSD in rotenone induced THP-1 macrophages, TSD inhibited the activation of caspase-1 and rotenone-induced NALP3 inflammasome activation in THP-1 macrophages. The results obtained in the current study revealed that TSD attenuated MSU crystal-induced inflammation by inhibiting rotenone-induced activation of the NALP3 inflammasome and caspase-1, suggesting that these two proteins may be novel targets for the treatment of gouty arthritis.

Sirt1 ameliorates monosodium urate crystal-induced inflammation by altering macrophage polarization via the PI3K/Akt/STAT6 pathway

OBJECTIVES

Acute gout is an inflammatory response to MSU crystals. In our previous research, Sirt1 was shown to have an effect in preventing acute gouty inflammation. In the current study, we aimed to investigate the underlying mechanism involving Sirt1 in acute gout.

METHODS

The cytological changes and Sirt1 expression in the synovium were observed in patients with acute or intermittent gout. The effect of Sirt1 and its mechanism in gout were studied in macrophages, C57BL/6 mice and Sirt1+/- mice.

RESULTS

Sirt1 expression was increased in the peripheral blood mononuclear cells (PBMCs) of patients with acute gout but not in the chronic tophus tissue. The arthritis score and numbers of inflammatory cells in injured paw tissue from murine gout models were upregulated in Sirt1+/- mice compared with wild-type mice. A PCR array of the paw tissue from murine gout models indicated that Sirt1 activation might attenuate MSU-induced inflammation by altering the polarization state of macrophages. Furthermore, in patients with acute gout, the phagocytosis of MSU crystals by a macrophage was found in a smear of the joint fluid and large amounts of macrophages were also found in the synovium. The activation of Sirt1 in gouty mice actually decreased the tendency toward M1 polarization. The inhibition of PI3K/Akt partially blocked the anti-inflammatory effect of Sirt1 and the translocation of STAT6, and phosphorylated STAT6 expression was decreased in RAW 264.7 cells treated with MSU crystals.

CONCLUSION

Our studies revealed that Sirt1 ameliorates MSU-induced inflammation by altering macrophage polarization via the PI3K/Akt/STAT6 pathway.

Discovery of novel and potent P2Y14R antagonists via structure-based virtual screening for the treatment of acute gouty arthritis

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A reliable Glide docking-based virtual screening (VS) pipeline for P2Y₁₄R was developed.

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Several potent P2Y₁₄R antagonists with novel scaffolds were identified utilizing the VS strategy.

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P2Y₁₄R inhibitory effect was evaluated by testing cAMP levels in HEK293 cells.

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Anti-gout activity of screened compound was detected in MSU-treated THP-1 cells.

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The mechanism of test compound in treating acute gouty arthritis was elucidated.

P2Y₁₄ nucleotide receptor is a Gi protein-coupled receptor, which is widely involved in physiological and pathologic events. Although several P2Y₁₄R antagonists have been developed thus far, few have successfully been developed into a therapeutic drug. In this study, on the basis of two P2Y₁₄R homology models, Glide docking-based virtual screening (VS) strategy was employed for finding potent P2Y₁₄R antagonists with novel chemical architectures. A total of 19 structurally diverse compounds identified by VS and drug-like properties testing were set to experimental testing. 10 of them showed good inhibitory effects against the P2Y₁₄R (IC₅₀ < 50 nM), including four compounds (compounds 8, 10, 18 and 19) with IC₅₀ value below 10 nM. The best VS hit, compound 8 exhibited the best antagonistic activity, with IC₅₀ value of 2.46 nM. More importantly, compound 8 restrained monosodium uric acid (MSU)-induced pyroptosis of THP-1 cells through blocking the activation of Nod-like receptor 3 (NLRP3) inflammasome, which was attributed to its inhibitory effects on P2Y₁₄R-cAMP pathways. The key favorable residues uncovered using MM/GBSA binding free energy calculations/decompositions were detected and discussed. These findings suggest that the compound 8 can be used as a good lead compound for further optimization to obtain more promising P2Y₁₄R antagonists for the treatment of acute gouty arthritis.

Hyperuricemia as a potential plausible risk factor for periodontitis

Elevated blood uric acid (UA) levels have been positively associated with the severity of periodontitis. It thus brings out a hypothesis that hyperuricemia, a pathological elevation of blood UA, might be a risk factor for periodontitis. Namely, periodontitis individuals with Hu might acquire more severe periodontal destruction compared to those without Hu. To support the hypothesis, four aspects of evidences are proposed. First, hyperuricemia and periodontitis share many metabolic and inflammatory comorbidities such as metabolic syndrome, diabetes and cardiovascular diseases which are commonly related to elevated UA levels and gout. Second, observational and interventional studies have found altered UA levels in blood and saliva in periodontitis patients or after periodontal treatment, suggesting an epidemiological connection between hyperuricemia and periodontitis. Third, plausible immuno-metabolic mechanisms by which hyperuricemia might promote the progression of periodontitis are suggested, such as impaired immune response, oxidative stress, pathological bone remodeling and dysbiosis. The last, our empirical data exhibited elevated UA levels in gingival tissue in periodontitis mice compared to controls. If the hypothesis is true, given the high prevalence of the two conditions, hyperuricemia would be a significant risk factor increasing the global burden of periodontal diseases. Evidences on a directional correlation between hyperuricemia and periodontitis are sparse. Longitudinal and experimental studies would be necessary to determine the magnitude of periodontal risk, if any, exacerbated by hyperuricemia and the underlying mechanisms.

Pharmacological basis for use of madecassoside in gouty arthritis: anti-inflammatory, anti-hyperuricemic, and NLRP3 inhibition

Objectives: Gouty arthritis is caused by the deposition of monosodium urate (MSU) crystals in joints, which is associated with the rise of serum urate content. This study aims to investigate the therapeutic effect of Madecassoside on gouty arthritis and hyperuricemia. Methods: DBA/1 mice were intradermally injected with MSU to stimulate joint inflammation or intraperitoneally injected with MSU to trigger peritonitis. Moreover, ICR mice were exposed to potassium oxonate to stimulate hyperuricemia. Results: Madecassoside repressed MSU-triggered pad swelling, joint 99mTc uptake, and joint inflammation in DBA/1 mice with gouty arthritis. Neutrophil infiltration and IL-1β & IL-6 & MCP-1 secretion was also alleviated in lavage fluids from DBA/1 mice with peritonitis due to Madecassoside treatment. Furthermore, Madecassoside decreased MSU-induced neutrophil cytosolic factor 1, caspase-1 and NLRP3 expression in mice with peritoneal inflammation. In hyperuricemic mice, Madecassoside improved renal dysfunction. Serum uric acid, BUN, and creatinine were down-regulated by Madecassoside. Conclusion: These findings indicate that Madecassoside has potential to ameliorate inflammation in both acute gouty arthritis model and peritonitis model, probably via regulating IL-1β and NLRP3 expression. Practical point: Madecassoside also exhibited a urate-lowering effect and a renal protective effect in hyperuricemic mice.

Monocyte to Lymphocyte Ratio, Neutrophil to Lymphocyte Ratio, and Red Cell Distribution Width are the Associates with Gouty Arthritis

BACKGROUND

Neutrophils, monocytes, and macrophages activations are associated with a gout attack. Monocyte to lymphocyte ratio (MLR), neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), red cell distribution width (RDW), and mean platelet volume (MPV) are well-known inflammation markers. In this study, we aimed to investigate whether they could be a predictive marker to the gout attack.

MATERIAL AND METHODS

A hundred and ten gout patients (male/female, 86/24) and 90 (male/female, 64/26) age-, gender-, and body mass index-matched volunteer controls were included in the study. Blood samples were obtained in the intercritical and attack period of the patients. Hemogram, serum uric acid (SUA), C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) values were studied.

RESULTS

In the attack period NLR (p < 0.001), PLR (p < 0.05), MLR (p < 0.001), RDW (p < 0.05), MPV (p < 0.05), ESR (p < 0.001), CRP (p < 0.001) and SUA (p < 0.001) values were significantly higher than intercritical period values. According to the results of regression analysis; There was an independent strong relationship between the gout attack and SUA, (Beta [β] = 0.352, p < 0.001), ESR (β = 0.329, p < 0.001), CRP (β = 0.286, p < 0.001), MLR (β = 0.126, p < 0.001), RDW (β = 0.100, p = 0.003) and NLR (β = 0.082, p = 0.014).

CONCLUSIONS

MLR, RDW, and NLR may be a strong predictive marker for a gout attack. MPV and PLR values in the gout attack may be associated with systemic inflammation.

DEL-1 promotes macrophage efferocytosis and clearance of inflammation

Resolution of inflammation is essential for tissue homeostasis and a promising approach to inflammatory disorders. Here we found that DEL-1, a secreted protein inhibiting leukocyte-endothelial adhesion and inflammation initiation, also functions as a non-redundant downstream effector in inflammation clearance. In human and murine periodontitis, waning of inflammation correlated with DEL-1 upregulation, whereas resolution of experimental periodontitis failed in DEL-1 deficiency. This concept was mechanistically substantiated in acute monosodium urate crystal-induced inflammation, where the pro-resolution function of DEL-1 was attributed to effective apoptotic neutrophil clearance (efferocytosis). DEL-1-mediated efferocytosis induced liver-X-receptor-dependent macrophage reprogramming to pro-resolving phenotype and was required for optimal production of at least certain specific pro-resolving mediators. Experiments in transgenic mice with cell-specific overexpression of DEL-1 linked its anti-leukocyte recruitment action to endothelial-derived DEL-1 and its efferocytic/pro-resolving action to macrophage-derived DEL-1. Thus, the compartmentalized expression of DEL-1 facilitates distinct homeostatic functions in an appropriate context that can be harnessed therapeutically.

Frontline Science: Reprogramming COX-2, 5-LOX, and CYP4A-mediated arachidonic acid metabolism in macrophages by salidroside alleviates gouty arthritis

Cyclooxygenase-2 (COX-2), 5-lipoxygenase (5-LOX), and cytochrome P450 (CYP) 4A-mediated arachidonic acid (AA) metabolism play an essential role in human inflammatory disorders. Blocking COX-2 pathway would shunt AA metabolism to the other pathway, thereby decreasing the efficacy and exacerbating adverse effects. Here we demonstrated that reprogramming COX-2, 5-LOX, and CYP4A-mediated AA metabolism in macrophages by salidroside (Sal) ameliorates monosodium urate (MSU) crystal-induced inflammation. Compared with COX-2 inhibitor celecoxib, Sal (80 mg/kg) presented a superior anti-arthritic profile in MSU crystal-treated rats, accompanied with the decreased expression of COX-2, 5-LOX, and CYP4A and production of prostaglandin E2 (PGE₂ ), leukotriene B4 (LTB₄ ), and 20-hydroxyeicosatetraenoic acid (20-HETE) in the synovial fluid macrophages. Sal decreased representative M1 marker (iNOS and CD86, etc.) expression and M1 cytokine (TNF-α and IL-1β) production, whereas it increased M2 marker (CD206 and Arg-1) expression and M2 cytokine (TGF-β and IL-10) production. The injection of conditioned medium from MSU crystal-treated macrophages into the ankle joint of rats reproduced the gouty inflammation, which was attenuated by Sal. Mechanistically, down-regulation of COX-2, 5-LOX, and CYP4A in the RAW264.7 and NR8383 macrophages by Sal skewed macrophage polarization away from the M1 phenotype, and thereby prevented neutrophil migration and chondrocyte degradation with STAT1 and NF-κB inactivation. Conversely, overexpression of COX-2, 5-LOX, CYP4A or STAT1, or exogenous addition of IL-1β or TNF-α partially abolished these effects. Together, inhibition of COX-2, 5-LOX, and CYP4A in macrophages by Sal ameliorates MSU crystal-induced inflammation through decreasing TNF-α and IL-1β production, and may serve as a novel therapeutic strategy.

Inhibition of COX-2/mPGES-1 and 5-LOX in macrophages by leonurine ameliorates monosodium urate crystal-induced inflammation

Cyclooxygenase-2 (COX-2), 5-lipoxygenase (5-LOX) and microsomal prostaglandin E synthase-1 (mPGES-1)-derived eicosanoids play an essential role in human inflammatory disorders. Here, we investigated whether inhibition of COX-2/mPGES-1 and 5-LOX in macrophages by leonurine ameliorates monosodium urate (MSU) crystal-induced inflammation. Virtual screening assay and in vitro enzyme inhibition assay showed that leonurine was a potential inhibitor of COX-2, mPGES-1 and 5-LOX. Compared with COX-2 inhibitor celecoxib, leonurine (30 mg/kg) significantly decreased ankle perimeter, gait score and neutrophil number in synovial fluid in MSU crystal-treated rats, accompanied with the decreased expression of COX-2, mPGES-1 and 5-LOX and production of prostaglandin E₂ (PGE₂) and leukotriene B₄ (LTB₄) in the synovial fluid macrophages. In addition, leonurine decreased representative M1 marker (iNOS and CD86) expression, NLRP3 inflammasome activation and M1 cytokine (TNF-α and IL-1β) production. In the in vitro cultured RAW264.7 and human monocyte-derived macrophages (MDMs), blockade of COX-2/mPGES-1 and 5-LOX by leonurine inhibited macrophage M1 polarization and NLRP3 inflammasome activation in response to MSU crystals, and thus down-regulated IL-1β and TNF-α with STAT1 and NF-κB inactivation. Conversely, these effects were partially abolished by overexpression of COX-2, mPGES-1, 5-LOX or STAT1. Furthermore, leonurine prevented a positive feedback loop between COX-2/mPGES-1/5-LOX and IL-1β/TNF-α in MSU crystal-induced inflammation. Together, simultaneous down-regulation of COX-2/mPGES-1 and 5-LOX by leonurine ameliorates MSU crystal-induced inflammation through decreasing IL-1β and TNF-α production. Our study may provide novel multi-target agents toward the arachidonic acid (AA) network for gouty arthritis therapy.

Ligand-mediated cytoplasmic retention of the Ah receptor inhibits macrophage-mediated acute inflammatory responses

The Ah receptor (AHR) has been shown to exhibit both inflammatory and anti-inflammatory activity in a context-specific manner. In vivo macrophage-driven acute inflammation models were utilized here to test whether the selective Ah receptor modulator 1-allyl-7-trifluoromethyl-1H-indazol-3-yl]-4-methoxyphenol (SGA360) would reduce inflammation. Exposure to SGA360 was capable of significantly inhibiting lipopolysaccharide (LPS)-mediated endotoxic shock in a mouse model, both in terms of lethality and attenuating inflammatory signaling in tissues. Topical exposure to SGA360 was also able to mitigate joint edema in a monosodium urate (MSU) crystal gout mouse model. Inhibition was dependent on the expression of the high-affinity allelic AHR variant in both acute inflammation models. Upon peritoneal MSU crystal exposure SGA360 pretreatment inhibited neutrophil and macrophage migration into the peritoneum. RNA-seq analysis revealed that SGA360 attenuated the expression of numerous inflammatory genes and genes known to be directly regulated by AHR in thioglycolate-elicited primary peritoneal macrophages treated with LPS. In addition, expression of the high-affinity allelic AHR variant in cultured macrophages was necessary for SGA360-mediated repression of inflammatory gene expression. Mechanistic studies revealed that SGA360 failed to induce nuclear translocation of the AHR and actually enhanced cytoplasmic localization. LPS treatment of macrophages enhanced the occupancy of the AHR and p65 to the Ptgs2 promoter, whereas SGA360 attenuated occupancy. AHR ligand activity was detected in peritoneal exudates isolated from MSU-treated mice, thus suggesting that the anti-inflammatory activity of SGA360 is mediated at least in part through AHR antagonism of endogenous agonist activity. These results underscore an important role of the AHR in participating in acute inflammatory signaling and warrants further investigations into possible clinical applications.

CD14+ Cells with the Phenotype of Infiltrated Monocytes Consist of Distinct Populations Characterized by Anti-inflammatory as well as Pro-inflammatory Activity in Gouty Arthritis

It has been suggested that inflammasome-mediated IL-1β production in monocytic cells is responsible for the acute inflammatory response in gouty arthritis. However, phenotypical and functional analyses of monocytes during gouty arthritis have yet to be conducted. Therefore, we investigated the characteristics of monocytes/macrophages in the synovial fluid cells of patients with acute gout. The number and frequency of monocytes/macrophages in the synovial fluid mononuclear cells (SFMCs) of patients was examined. The expression of markers for monocyte recruitment and tissue-resident macrophages, the production of pro-inflammatory and anti-inflammatory cytokines, and phagocytosis were analyzed in the monocytes/macrophages of patients with acute gout attacks. The number and frequency of CD14⁺CD3⁻CD19⁻CD56⁻ monocytes/macrophages was markedly increased in the SFMCs of patients with gout compared to those of patients with rheumatoid arthritis (RA). CD14⁺ cells showed the phenotypes of infiltrated monocytes rather than tissue-resident macrophages, characterized by a high expression of CCR2, MRP8, and MRP14, but a low expression of MERTK and 25F9. These cells had the capacity to produce pro-inflammatory cytokines such as TNF-α and IL-1β after stimulation with lipopolysaccharides. In addition, anti-inflammatory features, including CD163 expression and IL-10 production from CD14⁺ cells, were significantly higher in patients with gout than in those with RA. CD14⁺ cells with phenotype of M2 macrophages had high phagocytic activity for monosodium urate crystals. Thus, our results indicate that monocytes/macrophages from patients with gout have the phenotype of infiltrated monocytes, and these cells consist of different populations characterized by anti-inflammatory activities as well as pro-inflammatory functions.

Molecular Pathophysiology of Gout

Three contradictory clinical presentations of gout have puzzled clinicians and basic scientists for some time: first, the crescendo of sterile inflammation in acute gouty arthritis; second, its spontaneous resolution, despite monosodium urate (MSU) crystal persistence in the synovium; and third, immune anergy to MSU crystal masses observed in tophaceous or visceral gout. Here, we provide an update on the molecular pathophysiology of these gout manifestations, namely, how MSU crystals can trigger the auto-amplification loop of necroinflammation underlying the crescendo of acute gouty arthritis. We also discuss new findings, such as how aggregating neutrophil extracellular traps (NETs) might drive the resolution of arthritis and how these structures, together with granuloma formation, might support immune anergy, but yet promote tissue damage and remodeling during tophaceous gout.

Comparison of the Effects of a Pharmaceutical Industry Decision Guide and Decision Aids on Patient Choice to Intensify Therapy in Rheumatoid Arthritis

OBJECTIVE

To compare the effects a pharmaceutical industry decision guide and International Patient Decision Aids Standard (IPDAS) compliant patient decision aids (PtDA) on patient medication beliefs and choice to intensify therapy.

METHODS

Rheumatoid arthritis (RA) patients, who had never taken etanercept (Enbrel), took part in a mail survey. They were presented with a hypothetical decision scenario where they were asked to consider adding etanercept to their current regimen. Each patient was randomized to review 1 of 3 forms of an etanercept-specific decision support: a long PtDA (LONG DA), a short PtDA (SHORT DA), or the manufacturer's Enbrel decision guide (Pharm Booklet).

RESULTS

We had 402 RA patients participate in the study (response rate, 52%). Of the patients randomized to the Pharm Booklet, 30.6% elected to initiate etanercept. Only 14.6% and 14.0% of patients who reviewed the LONG DA or SHORT DA choose to take etanercept (χ2 = 15.7; P < 0.001). Patients who reviewed the LONG DA or SHORT DA had a greater increase in knowledge about etanercept than those who reviewed the Pharm Booklet. There was no difference in decisional conflict among the groups. A logistic regression model explained 44.2% (R2 = 0.442) of patient choice to intensify therapy by initiating etanercept. The strongest predictor of choice to intensify therapy were beliefs about etanercept's ability to improve symptoms (OR = 2.56, 96%CI [1.71, 3.80]), and its use by others like the respondent (OR = 2.24, 95%CI [1.49, 3.35]). Mediation analysis confirmed the presence of a partial mediating effect of decision support on patients' intent to take etanercept (OR = 0.59, 95%CI [0.39, 0.89]).

CONCLUSIONS

Patients supported by the Pharm Booklet were twice as likely to choose to intensify therapy. The Pharm Booklet's effects are partially mediated through persuasive communication techniques that influence patients' beliefs that symptoms will improve, and increase social normative beliefs, rather than by increasing the relevant knowledge, clarifying patient values about positive or negative treatment outcomes, or increasing their self-efficacy.

Interleukin 37 limits monosodium urate crystal-induced innate immune responses in human and murine models of gout

Background

Interleukin (IL)-37 has emerged as a fundamental inhibitor of innate immunity. Acute gout is a self-limiting inflammatory response to monosodium urate (MSU) crystals. In the current study, we assessed the preventive and therapeutic effect of recombinant human IL-37 (rhIL-37) in human and murine gout models.

Methods

We investigated the expression of IL-37 in patients with active and inactive gouty arthritis and assessed the effect of rhIL-37 in human and murine gout models: a human monocyte cell line (THP-1) and human synovial cells (containing macrophage-like and fibroblast-like synoviocytes) exposed to MSU crystals, a peritoneal murine model of gout and a murine gouty arthritis model. After inhibition of Mer receptor tyrosine kinase (Mertk), levels of IL-1β, IL-8 and chemokine (C-C motif) ligand 2 (CCL-2) were detected by ELISA and expression of mammalian homologs of the drosophila Mad gene 3 (Smad), suppressor of cytokine signaling 3 (SOCS3), NACHT-LRR-PYD-containing protein 3 (NLRP3), and IL-8R of THP-1 were assessed by qPCR and western blot to explore the molecular mechanisms.

Results

Our studies strongly indicated that rhIL-37 played a potent immunosuppressive role in the pathogenesis of experimental gout models both in vitro and in vivo, by downregulating proinflammatory cytokines and chemokines, markedly reducing neutrophil and monocyte recruitment, and mitigating pathological joint inflammation. In our studies, rhIL-37 suppressed MSU-induced innate immune responses by enhancing expression of Smad3 and IL-1R8 to trigger multiple intracellular switches to block inflammation, including inhibition of NLRP3 and activation of SOCS3. Mertk signaling participated in rhIL-37 inhibitory pathways in gout models. By inhibition of Mertk, the anti-inflammatory effect of rhIL-37 was partly abrogated, and IL-1R8, Smad3 and S​OCS3 expression were suppressed, whereas NLRP3 expression was reactivated.

Conclusions

Our studies reveal that IL-37 limits runaway inflammation initiated by MSU crystal-induced immune responses, partly in a Mertk-dependent fashion. Thus, rhIL-37 has both preventive and therapeutic effects in gouty arthritis.

Cytokine Profile in Gout: Inflammation Driven by IL-6 and IL-18?

INTRODUCTION

Gout is considered to be an autoinflammatory disease and the presence of monosodium urate (MSU) crystals stimulates activation of NPRL3 inflammasome and subsequently caspase-1, generating production of active IL-1β and IL-18. However, the association between serum cytokines levels and clinical manifestations of the disease is not yet well understood. We evaluated the serum profile of proinflammatory cytokines (IL-1β, IL-6, IL-8, IL-17A, IL-18, IL-22, and IL-23) and described their relationship with clinical and laboratory data.

METHODOLOGY

Thirty-nine male patients with gout (GG) were assessed for clinical and laboratory variables and cytokine levels were measured by ELISA. For the purposes of comparison, 34 males with no previous history of arthritis were also included in the study (CG).

RESULTS

Seventeen participants (43%) exhibited active arthritis on evaluation. Levels of IL-18 were significantly higher in patients in relation to the CG (p = 0.0013). No statistically significant differences were found between the GG and CG for the other measured cytokines. There was a moderate correlation between IL-18 and ESR (R = 0.43, p = 0.0073), CRP (R = 0.47, p = 0.0025), and serum levels of IL-6 (R = 0.36, p = 0.023). An association was observed between serum levels of IL-6 and the presence of tophi (p = 0.005) and deformities (p = 0.0008), as well as a correlation between this cytokine and ESR (R = 0.41, p = 0.011) and CRP (R = 0.48, p = 0.02).

CONCLUSIONS

IL-18 is associated with inflammatory activity in gout, as well as with IL-6 levels, while IL-6 is associated with clinical and laboratory activity, the presence of tophi and articular deformities, and may be a prognostic marker of this pathology.

The role of tissue resident cells in neutrophil recruitment

Neutrophils are first responders of the immune system, rapidly migrating into affected tissues in response to injury or infection. To effectively call in this first line of defense, strategically placed cells within the vasculature and tissue respond to noxious stimuli by sending out coordinated signals that recruit neutrophils. Regulation of organ-specific neutrophil entry occurs at two levels. First, the vasculature supplying the organ provides cues for neutrophil egress out of the bloodstream in a manner dependent upon its unique cellular composition and architectural features. Second, resident immune cells and stromal cells within the organ send coordinated signals that guide neutrophils to their final destination. Here, we review recent findings that highlight the importance of these tissue-specific responses in the regulation of neutrophil recruitment and the initiation and resolution of inflammation.

Differential proteomics of monosodium urate crystals-induced inflammatory response in dissected murine air pouch membranes by iTRAQ technology

The precipitation of monosodium urate crystals within joints triggers an acute inflammatory reaction that is the root cause of gout. The inflammation induced by the injection of MSU crystals into the murine air pouch for 1, 3, and 5 h was examined by iTRAQ-based proteomic profiling. The iTRAQ-labeled peptides were fractionated by SCX, basic-RP or solution-IEF, followed by LC-MS/MS analysis. A total of 951 proteins were quantified from the total combined fractions. Among them, 317 proteins exhibited a differential expression, compared to that of the controls at one time point or more. The majority of the differentially expressed proteins were found in the sample after a 5-h MSU treatment. Western blot revealed that the expression levels of cathelin-related antimicrobial peptide and S100A9 were positively correlated with the time-course treated with MSU. Further analysis of GeneGO pathway demonstrated that these differentially expressed proteins are primarily related to the immune-related complement system and the tricarboxylic acid cycle. Moreover, seven genes from the TCA cycle were found to be significantly downregulated at the transcriptional level and its correlation with gout and possible therapeutic applications are worth further investigation. Last, we found that pyruvate carboxylation could be potential targets for antigout treatment.

Colchicine: old and new

Although colchicine has been a focus of research, debate, and controversy for thousands of years, the US Food and Drug Administration just approved it in 2009. Over the past decade, advances in the knowledge of colchicine pharmacology, drug safety, and mechanisms of action have led to changes in colchicine dosing and to potential new uses for this very old drug. In this review, we discuss the pharmacologic properties of colchicine and summarize what is currently known about its mechanisms of action. We then discuss and update the use of colchicine in a variety of illnesses, including rheumatic and, most recently, cardiovascular diseases.

Animal model of acute gout reproduces the inflammatory and ultrasonographic joint changes of human gout

INTRODUCTION

Gout is an inflammatory condition induced by the deposition of monosodium urate (MSU) crystals in the joints and soft tissues that can produce acute or chronic arthritis. Several animal models of crystal-induced inflammation have been proposed that involve direct injection of MSU-crystals into different anatomical structures; however, only a few of these models reflect a true diarthrodial joint microenvironment in which an acute gouty attack takes place. The aim of this study was to assess the inflammatory and structural joint changes in a rabbit model of acute gout attack by ultrasound (US), synovial fluid (SF) and histopathological analyses.

METHODS

Under US guidance, 42 rabbit knees were randomly injected with a suspension of 50 mg/ml of either MSU or allopurinol synthetic crystals. The control group received intra-articular vehicle of phosphate-buffered saline (PBS). US evaluation, SF and histopathological analyses were performed at days 1, 3, and 7.

RESULTS

A total of 21 rabbit knees were assigned to the control group, 12 to the MSU-crystals group, and 9 to the allopurinol crystals group. By US, the MSU crystals group displayed the double contour sign and bright stippled aggregates in 67% and 75% of joints, respectively. Neither control knees nor allopurinol crystals group displayed these US signs. Power Doppler (PD) signal was moderate to intense in the MSU-crystals group and greater than both the allopurinol crystal and control groups at day 1 (P<0.001) and 3 (P<0.05), with its practical disappearance by day 7. SF leukocyte count was 40,312±6,369 cells/mm3 in the MSU-crystals group, higher than in controls (P=0.004) and allopurinol crystal group (P=0.006). At day 7, SF leukocyte count decreased in both MSU and allopurinol crystal groups reaching the non-inflammatory range. Histologically, at day 3 intense synovial polymorphonuclear cells infiltration and MSU aggregates were identified.

CONCLUSION

The rabbit model of MSU crystal-induced acute arthritis efficiently reproduces the inflammatory, US, SF and histopathological changes of the human acute gouty attack.

Small heterodimer partner interacts with NLRP3 and negatively regulates activation of the NLRP3 inflammasome

Excessive activation of the NLRP3 inflammasome results in damaging inflammation, yet the regulators of this process remain poorly defined. Herein, we show that the orphan nuclear receptor small heterodimer partner (SHP) is a negative regulator of NLRP3 inflammasome activation. NLRP3 inflammasome activation leads to an interaction between SHP and NLRP3, proteins that are both recruited to mitochondria. Overexpression of SHP competitively inhibits binding of NLRP3 to apoptosis-associated speck-like protein containing a CARD (ASC). SHP deficiency results in increased secretion of proinflammatory cytokines IL-1β and IL-18, and excessive pathologic responses typically observed in mouse models of kidney tubular necrosis and peritoneal gout. Notably, the loss of SHP results in accumulation of damaged mitochondria and a sustained interaction between NLRP3 and ASC in the endoplasmic reticulum. These data are suggestive of a role for SHP in controlling NLRP3 inflammasome activation through a mechanism involving interaction with NLRP3 and maintenance of mitochondrial homeostasis.