Recent advances in nanocrystals for arthritis drug delivery

INTRODUCTION

More than 500 million people worldwide suffer from arthritis, experiencing daily pain and inflammation. Current treatments for osteoarthritis (OA) and rheumatoid arthritis (RA) are palliative, offering only symptom relief. No disease-modifying OA drugs (DMOADs) capable of restoring joint functionality and regenerating the cartilage matrix have yet been approved by the FDA or EMA.

AREAS COVERED

This review highlights recent advances in nanocrystals (NCs) for arthritis drug delivery, including conventional nanosuspensions and novel transdermal microneedles. Special attention is given to intra-articular DMOADs formulated as NC-in-microparticles, designed to extend drug release over months. Papers and reviews with the mentioned contents and published over the last 5 years were included in the review process.

EXPERT OPINION

New DMOADs and disease-modifying antirheumatic drugs (DMARDs) are often poorly water-soluble, limiting their clinical progress. The versatility of NCs and nanosuspensions offers a potential advantage over other types of nanoparticles, as they can be adapted to various delivery systems, administration routes, and types of arthritis. Due to the avascular nature of cartilage, exploring the intra-articular route for OA management is essential. Implementing cartilage-targeted strategies or using stimuli-responsive hydrogels can further enhance their therapeutic potential.

Targeting the NLRP3 inflammasome as a novel therapeutic target for osteoarthritis

Osteoarthritis, the most common arthritic condition, is an age-related progressive disease characterized by the loss of cartilage and synovial inflammation in the knees and hips. Development of pain, stiffness, and considerably restricted mobility of the joints are responsible for the production of matrix metalloproteinases and cytokines. Although several treatments are available for the management of this disease condition, they possess limitations at different levels. Recently, efforts have focused on regulating the production of the NLRP3 inflammasome, which plays a critical role in the disease's progression due to its dysregulation. Inhibition of NLRP3 inflammasome has shown the potential to modulate the production of MMP-13, caspase-1, IL-1β, etc., which has been reflected by positive responses in different preclinical and clinical studies. Aiming inhibition of this NLRP3 inflammasome, several compounds are in different stages of research owing to bring a novel agent for the treatment of osteoarthritis. This review summarizes the mechanistic pathways linking NLRP3 activation to osteoarthritis development and discusses the progress in new therapeutics aimed at effective treatment.

Pyroptosis-related crosstalk in osteoarthritis: Macrophages, fibroblast-like synoviocytes and chondrocytes

The pathogenesis of osteoarthritis (OA) involves a multifaceted interplay of inflammatory processes. The initiation of pyroptosis involves the secretion of pro-inflammatory cytokines and has been identified as a critical factor in regulating the development of OA. Upon initiation of pyroptosis, a multitude of inflammatory mediators are released and can be disseminated throughout the synovial fluid within the joint cavity, thereby facilitating intercellular communication across the entire joint. The main cellular components of joints include chondrocytes (CC), fibroblast-like synoviocytes (FLS) and macrophages (MC). Investigating their interplay can enhance our understanding of OA pathogenesis. Therefore, we comprehensively examine the mechanisms underlying pyroptosis and specifically investigate the intercellular interactions associated with pyroptosis among these three cell types, thereby elucidating their collective contribution to the progression of OA. We propose the concept of ' CC-FLS-MC pyroptosis-related crosstalk', describe the various pathways of pyroptotic interactions among these three cell types, and focus on recent advances in intervening pyroptosis in these three cell types for treating OA. We hope this will provide a possible direction for diversification of treatment for OA. The Translational potential of this article. The present study introduces the concept of 'MC-FLS-CC pyroptosis-related crosstalk' and provides an overview of the mechanisms underlying pyroptosis, as well as the pathways through which it affects MC, FLS, and CC. In addition, the role of regulation of these three types of cellular pyroptosis in OA has also been concerned. This review offers novel insights into the interplay between these cell types, with the aim of providing a promising avenue for diversified management of OA.

Mechanisms of NLRP3 inflammasome in rheumatoid arthritis and osteoarthritis and the effects of traditional Chinese medicine

ETHNOPHARMACOLOGICAL RELEVANCE

It has been widely reported that various anti-rheumatic traditional Chinese medicines (TCMs) ameliorate rheumatoid arthritis (RA) and osteoarthritis (OA) through regulating the abnormal production, assembly, and activation of the NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome. These TCMs include monomers isolated from Chinese herbs, extracts of Chinese herbs, and Chinese medical formulae with a lengthy application history.

AIM OF THE STUDY

This review aimed to summarize and analyze the published articles about the NLRP3 inflammasome and its role in the pathogenesis of RA and OA. We also reviewed existing knowledge on the therapeutic mechanism of TCMs in RA and OA via the regulation of the NLRP3 inflammasome.

MATERIALS AND METHODS

We searched for relevant articles with the keywords "NLRP3 inflammasome", "traditional Chinese medicine," "Chinese herbal drugs," "rheumatoid arthritis," and "osteoarthritis." The information retrieval was conducted in medical Chinese and English databases from the date of construction to April 19, 2023, including PubMed, MEDLINE, Web of Science, Scopus, Ovid, China National Knowledge Infrastructure (CNKI), Chinese Biomedicine Literature Database (CBM), Chinese Science and Technology Periodicals Database (VIP), and China Online Journals (COJ).

RESULTS

According to retrieval results, 35 TCMs have been demonstrated to relieve RA by targeting the NLRP3 inflammasome, including six traditional Chinese prescriptions, seven extracts of Chinese herbs, and 22 monomers extracted from traditional Chinese herbs and formulae. Additionally, 23 TCMs have shown anti-OA effects with abilities to modulate the NLRP3 inflammasome, including five traditional Chinese prescriptions, one extract of Chinese herbs, and 17 monomers from Chinese herbs.

CONCLUSIONS

We summarized mechanism research about the pivotal roles of the NLRP3 inflammasome in the pathogenesis of RA and OA. Moreover, a review of TCMs with targets of the NLRP3 inflammasome in RA and OA treatment was also conducted. Our work is conducive to a better application of TCMs in complementary and alternative therapies in RA and OA.

Targeting macrophagic PIM-1 alleviates osteoarthritis by inhibiting NLRP3 inflammasome activation via suppressing mitochondrial ROS/Cl- efflux signaling pathway

BACKGROUND

Osteoarthritis (OA), in which macrophage-driven synovitis is considered closely related to cartilage destruction and could occur at any stage, is an inflammatory arthritis. However, there are no effective targets to cure the progression of OA. The NOD-, LRR-,and pyrin domain-containing protein 3 (NLRP3) inflammasome in synovial macrophages participates in the pathological inflammatory process and treatment strategies targeting it are considered to be an effective approach for OA. PIM-1 kinase, as a downstream effector of many cytokine signaling pathways, plays a pro-inflammatory role in inflammatory disease.

METHODS

In this study, we evaluated the expression of the PIM-1 and the infiltration of synovial macrophages in the human OA synovium. The effects and mechanism of PIM-1 were investigated in mice and human macrophages stimulated by lipopolysaccharide (LPS) and different agonists such as nigericin, ATP, Monosodium urate (MSU), and Aluminum salt (Alum). The protective effects on chondrocytes were assessed by a modified co-culture system induced by macrophage condition medium (CM). The therapeutic effect in vivo was confirmed by the medial meniscus (DMM)-induced OA in mice.

RESULTS

The expression of PIM-1 was increased in the human OA synovium which was accompanied by the infiltration of synovial macrophages. In vitro experiments, suppression of PIM-1 by SMI-4a, a specific inhibitor, rapidly inhibited the NLRP3 inflammasome activation in mice and human macrophages and gasdermin-D (GSDME)-mediated pyroptosis. Furthermore, PIM-1 inhibition specifically blocked the apoptosis-associated speck-like protein containing a CARD (ASC) oligomerization in the assembly stage. Mechanistically, PIM-1 inhibition alleviated the mitochondrial reactive oxygen species (ROS)/chloride intracellular channel proteins (CLICs)-dependent Cl- efflux signaling pathway, which eventually resulted in the blockade of the ASC oligomerization and NLRP3 inflammasome activation. Furthermore, PIM-1 suppression showed chondroprotective effects in the modified co-culture system. Finally, SMI-4a significantly suppressed the expression of PIM-1 in the synovium and reduced the synovitis scores and the Osteoarthritis Research Society International (OARSI) score in the DMM-induced OA model.

CONCLUSIONS

Therefore, PIM-1 represented a new class of promising targets as a treatment of OA to target these mechanisms in macrophages and widened the road to therapeutic strategies for OA.

Mechanism of NLRP3 inflammasome intervention for synovitis in knee osteoarthritis: A review of TCM intervention

Objective: This paper briefly reviews the structure and function of NLRP3 inflammasomes, signaling pathway, relationship with synovitis in KOA, and intervention of traditional Chinese medicine (TCM) in NLRP3 inflammasomes as a means to improve its therapeutic potential and clinical application.

Method: Literatures about NLRP3 inflammasomes and synovitis in KOA were reviewed to analyze and discuss.

Result: NLRP3 inflammasome can activate NF-κB mediated signal transduction, which in turn causes the expression of proinflammatory cytokines, initiates the innate immune response, and triggers synovitis in KOA. The TCM monomer/active ingredient, decoction, external ointment, and acupuncture regulating NLRP3 inflammasomes are helpful to alleviate synovitis in KOA.

Conclusion: The NLRP3 inflammasome plays a significant role in the pathogenesis of synovitis in KOA, TCM intervention targeting the NLRP3 inflammasome can be a novel approach and therapeutic direction for the treatment of synovitis in KOA.

The Role of Inflammasomes in Osteoarthritis and Secondary Joint Degeneration Diseases

Osteoarthritis is age-related and the most common form of arthritis. The main characteristics of the disease are progressive loss of cartilage and secondary synovial inflammation, which finally result in pain, joint stiffness, and functional disability. Similarly, joint degeneration is characteristic of systemic inflammatory diseases such as rheumatoid arthritis and gout, with the associated secondary type of osteoarthritis. Studies suggest that inflammation importantly contributes to the progression of the disease. Particularly, cytokines TNFα and IL-1β drive catabolic signaling in affected joints. IL-1β is a product of inflammasome activation. Inflammasomes are inflammatory multiprotein complexes that propagate inflammation in various autoimmune and autoinflammatory conditions through cell death and the release of inflammatory cytokines and damage-associated molecule patterns. In this article, we review genetic, marker, and animal studies that establish inflammasomes as important drivers of secondary arthritis and discuss the current evidence for inflammasome involvement in primary osteoarthritis. The NLRP3 inflammasome has a significant role in the development of secondary osteoarthritis, and several studies have provided evidence of its role in the development of primary osteoarthritis, while other inflammasomes cannot be excluded. Inflammasome-targeted therapeutic options might thus provide a promising strategy to tackle these debilitating diseases.

The Effect of Size of Materials Formed or Implanted In Vivo on the Macrophage Response and the Resultant Influence on Clinical Outcome

Both the chemistry and size of a material formed in vivo, or an implanted biomaterial, can alter the in vivo host response. Within the size range covered within this review, over 1 μm, chemistry is only important if the solid material is unstable and leeching small molecules. The macrophage activity and the resultant inflammatory response, however, are related to the size of the solid material. The premise of this review is that differences in size of the solid material, in different cases, can be the reason why there is some individual-to-individual variation in response. Specifically, the inflammatory response is enhanced when the size is between 1-50 μm. This will be looked at for three configurations: spherical particulate (silicone oil or gel from breast implants), elongated particulate (monosodium urate [MSU] crystals in gout or in kidney stones), and fibers (e.g., polyester used in fabric implants). These specific examples were selected because many still believe that the clinical outcome for each is controlled by the surface chemistry, when in fact it is the size. In each case, specific studies will be highlighted to either show a mechanism for creating different sizes and therefore a differential biological response (first three) or how changing the size and shape (diameter and spacing of fibers, in this example) can affect the response and can help explain the different responses to fabric implants found in vivo within the 1-50 μm size range. It was found that polyester fibers under 70 μm had a significant increase in macrophage response. Further, it was found that compounds found in synovial fluid could limit MSU crystal size. In addition, it was shown that plasma with low triglyceride levels emulsifies silicone oils to a greater extent than plasma with higher triglyceride levels. Therefore, in three cases it appears that differences in the inflammatory response between individuals and between different implants could be explained just by the size of the material formed or implanted.

The Damage-Associated Molecular Patterns (DAMPs) as Potential Targets to Treat Osteoarthritis: Perspectives From a Review of the Literature

During the osteoarthritis (OA) process, activation of immune systems, whether innate or adaptive, is strongly associated with low-grade systemic inflammation. This process is initiated and driven in the synovial membrane, especially by synovium cells, themselves previously activated by damage-associated molecular patterns (DAMPs) released during cartilage degradation. These fragments exert their biological activities through pattern recognition receptors (PRRs) that, as a consequence, induce the activation of signaling pathways and beyond the release of inflammatory mediators, the latter contributing to the vicious cycle between cartilage and synovial membrane. The primary endpoint of this review is to provide the reader with an overview of these many molecules categorized as DAMPs and the contribution of the latter to the pathophysiology of OA. We will also discuss the different strategies to control their effects. We are convinced that a better understanding of DAMPs, their receptors, and associated pathological mechanisms represents a decisive issue for degenerative joint diseases such as OA.

Pyroptosis Plays a Role in Osteoarthritis

Recent studies have revealed novel forms of cell death beyond the canonical types of cellular apoptosis and necrosis, and these novel forms of cell death are induced by extreme microenvironmental factors. Pyroptosis, a type of regulated cell death, occurs when pattern recognition receptors (PRRs) induce the activation of cysteine-aspartic protease 1 (caspase-1) or caspase-11, which can trigger the release of the pyrogenic cytokines interleukin-1β (IL-1β) and IL-18. Osteoarthritis (OA), the most common joint disease worldwide, is characterized by low-grade inflammation and increased levels of cytokines, including IL-1β and IL-18. Additionally, some damaged chondrocytes associated with OA exhibit morphological changes consistent with pyroptosis, suggesting that this form of regulated cell death may contribute significantly to the pathology of OA. This review summarizes the molecular mechanisms of pyroptosis and shows the critical role of NLRP3 (NLR family, pyrin domain containing 3; NLR refers to "nucleotide-binding domain, leucine-rich repeat") inflammasomes. We also provide evidence describing potential role of pyroptosis in OA, including the relationship with OA risk factors and the contribution to cartilage degradation, synovitis and OA pain.

The role of serum uric acid in the prediction of graft-versus-host disease in allogeneic hematopoietic stem cell transplantation

Background

Uric acid (UA) level is of the valuable signs of inflammation. However, the role of UA in the outcomes of hematopoietic stem cell transplantation (HSCT) such as GVHD and patients’ overall survival is still a matter of debate. In this study, we aimed to evaluate the relationship between UA levels and GVHD incidence and overall survival in allogeneic HSCT patients.

Methods

A total of 201 patients who were admitted for allogeneic transplantation at Taleghani hospital, Tehran, Iran, were considered for retrospective analysis. Serum UA levels from 1 week before transplantation until 2 weeks after transplantation were used to determine thresholds and find out the association of serum UA levels with GVHD and overall survival.

Results

We showed that the determined thresholds using receiver operating characteristic curves have poor predictive value for GVHD and overall survival. The patients with serum UA higher than 3.4 mg/dL had 37% lower odds of GVHD incidence and 35% lower hazard of death than patients with UA lower than 3.4 mg/dL.

Conclusion

Our results indicated that serum UA levels lower than 3.4 mg/dL could significantly increase the incidence of GVHD and hazard of death. The antioxidant functions of UA could explain the lower incidence of GVHD in hyperuricemic patients. However, the inconsistencies of the previous studies require further investigation to elucidate the role of UA in the prediction of GVHD.

MSU Crystals induce sterile IL-1β secretion via P2X7 receptor activation and HMGB1 release

BACKGROUD

The mechanism by which monosodium urate (MSU) crystals induce inflammation is not completely understood. Few studies have shown that MSU is capable of stimulating the release of IL-1β in the absence of LPS treatment. The purinergic P2X7 receptor is involved in the release of IL-1β in inflammatory settings caused by crystals, as is the case in silicosis.

METHODS

We investigated the role of P2X7 receptor in sterile MSU-induced inflammation by evaluating peritonitis and paw edema. In in vitro models, we performed the experiments using peritoneal macrophages and THP-1 cells. We measured inflammatory parameters using ELISA and immunoblotting. We measured cell recruitment using cell phenotypic identification and hemocytometer counts.

RESULTS

Our in vivo data showed that animals without P2X7 receptors generated less paw edema, less cell recruitment, and lower levels of IL-1β release in a peritonitis model. In the in vitro model, we observed that MSU induced dye uptake by the P2X7 receptor. In the absence of the receptor, or when it was blocked, MSU crystals induced less IL-1β release and this effect corresponded to the concentration of extracellular ATP. Moreover, MSU treatment induced HMGB1 release; pre-treatment with P2X7 antagonist reduced the amount of HMGB1 in cell supernatants.

CONCLUSIONS

IL-1β secretion induced by MSU depends on P2X7 receptor activation and involves HMGB1 release.

GENERAL SIGNIFICANCE

We propose that cell activation caused by MSU crystals induces peritoneal macrophages and THP-1 cells to release ATP and HMGB1, causing IL-1β secretion via P2X7 receptor activation.

Downregulation of calponin 2 contributes to the quiescence of lung macrophages

Calponin 2 is an actin cytoskeleton-associated regulatory protein that inhibits the activity of myosin-ATPase and cytoskeleton dynamics. Recent studies have demonstrated that deletion of calponin 2 restricts the proinflammatory activation of macrophages in atherosclerosis and arthritis to attenuate the disease progression in mice. Here we demonstrate that the levels of calponin 2 vary among different macrophage populations, which may reflect their adaptation to specific tissue microenvironment corresponding to specific functional states. Interestingly, lung resident macrophages express significantly lower calponin 2 than peritoneal resident macrophages, which correlates with decreased substrate adhesion and reduced expression of proinflammatory cytokines and a proresolution phenotype. Deletion of calponin 2 in peritoneal macrophages also decreased substrate adhesion and downregulated the expression of proinflammatory cytokines. Providing the first line of defense against microbial invasion while receiving constant exposure to extrinsic antigens, lung macrophages need to maintain a necessary level of activity while limiting exaggerated inflammatory reaction. Therefore, their low level of calponin 2 may reflect an important physiological adaption. Downregulation of calponin 2 in macrophages may be targeted as a cytoskeleton-based novel mechanism, possibly via endoplasmic reticulum stress altering the processing and secretion of cytokines, to regulate immune response and promote quiescence for the treatment of inflammatory diseases.

Elevated Interleukin 1β and Interleukin 6 Levels in the Serum of Children With Hyperuricemia

PURPOSES

The aim of this study was to investigate the serum levels and clinical significance of interleukin 1β (IL-1β) and IL-6 in children with hyperuricemia (HUA).

METHODS

We included 71 children with HUA and 71 children with no HUA as control subjects. Children with HUA were divided into groups I and II according to whether they had a history of acute gout-like attacks (including sudden monoarthritis of rapid onset with intense pain and swelling). Group I was examined twice (A, in the acute phase; B, in the remission phase). Serum IL-1β and IL-6 levels were measured by enzyme-linked immunosorbent assay.

RESULTS

Serum IL-1β and IL-6 levels were increased in children with HUA and were overall statistically different from the control group (P < 0.05, respectively). Serum IL-1β and IL-6 were significantly higher in group IA in comparison with group IB, group II, and control subjects (P < 0.05, respectively), as well as in groups IB and II compared with control subjects (P < 0.05, respectively). In group IB, the serum IL-1β and IL-6 concentrations were higher than those in group II, but there were no statistical differences (P > 0.05). In addition, in children with HUA, serum IL-1β and IL-6 levels were positively associated with white blood cell count, neutrophil count, monocyte count, uric acid levels, erythrocyte sedimentation rate, C-reactive protein, blood urea nitrogen, and serum creatinine levels (all P < 0.05), but were not associated with triglycerides, total cholesterol, low-density lipoprotein cholesterol, or high-density lipoprotein cholesterol levels (all P > 0.05).

CONCLUSION

IL-1β and IL-6 levels are increased in children with hyperuricemia, even if they have not had acute gout. Further studies are necessary to fully characterize the significance of IL-1β and IL-6 found in HUA children, and whether they could be correlated with long-term prognosis.

NLRP3 as a potentially novel biomarker for the management of osteoarthritis

Osteoarthritis (OA) was previously thought of as 'wear and tear' as humans age, however there is increasing evidence to support an inflammatory theory. The nucleotide-binding and oligomerization domain-like receptor containing protein 3 (NLRP3) inflammasome has been implicated in the pathogenesis of a number of arthritic disorders, producing proinflammatory cytokines and degradative enzymes such as Interleukin-1 beta (IL-1β), Tumour necrosis factor alpha (TNF-α) and Matrix metalloproteinase-3 (MMP-3) which drive cartilage degeneration and synovial inflammation. This review aims to summarise the evidence of NLRP3 involvement in OA. Currently, treatment options focus on management of the disease and to date there is no cure. The development of novel biomarkers for OA could improve diagnosis, treatment and management. Importantly, this review provides detail on the involvement of the NLRP3 inflammasome in OA pathology and how its members could act as potential biomarkers to assist clinical decisions.

Neutrophil: A Cell with Many Roles in Inflammation or Several Cell Types?

Neutrophils are the most abundant leukocytes in the circulation, and have been regarded as first line of defense in the innate arm of the immune system. They capture and destroy invading microorganisms, through phagocytosis and intracellular degradation, release of granules, and formation of neutrophil extracellular traps after detecting pathogens. Neutrophils also participate as mediators of inflammation. The classical view for these leukocytes is that neutrophils constitute a homogenous population of terminally differentiated cells with a unique function. However, evidence accumulated in recent years, has revealed that neutrophils present a large phenotypic heterogeneity and functional versatility, which place neutrophils as important modulators of both inflammation and immune responses. Indeed, the roles played by neutrophils in homeostatic conditions as well as in pathological inflammation and immune processes are the focus of a renovated interest in neutrophil biology. In this review, I present the concept of neutrophil phenotypic and functional heterogeneity and describe several neutrophil subpopulations reported to date. I also discuss the role these subpopulations seem to play in homeostasis and disease.

Human parvovirus B19 nonstructural protein NS1 activates NLRP3 inflammasome signaling in adult‑onset Still's disease

Dysregulation of inflammasomes serves a pathogenic role in autoinflammatory diseases (AIDs) and adult-onset Still's disease (AOSD) has been categorized as an AID. The present study investigated the expression of NLR family pyrin domain containing proteins (NLRPs) inflammasome in patients with AOSD, the effect of inflammasome inhibitors on NLRP3 signaling and whether human parvovirus B19‑associated antigens can activate NLRP3 in patients with AOSD. mRNA expression levels of NLRPs in peripheral blood mononuclear cells (PBMCs) from 34 patients with AOSD and 14 healthy individuals were determined using reverse transcription‑quantitative polymerase chain reaction. Protein expression of NLRP3 was evaluated by western blotting. Supernatant cytokine levels were measured by ELISA. Among the NLRPs investigated in the present study, NLRP3 transcripts were markedly elevated and expression of NLRP2, NLRP7 and NLRP12 was decreased in patients with AOSD compared with the controls. Treatment with NLRP3 inhibitors significantly reduced downstream NLRP3 signaling in PBMCs form patients with AOSD. B19‑nonstructural protein (NS)1 stimulation of PBMCs from patients with AOSD induced significant upregulation of transcript levels of NLRP3, caspase‑1 and interleukin (IL)‑1β compared with PBMCs from healthy controls. B19‑NS1 stimulation of PBMCs from patients with AOSD induced significant increase in supernatant levels of IL‑1β and protein expression of NLRP3, caspase‑1, IL‑1β, and IL‑18 compared with healthy controls. Elevated expression of NLRP3 and its downstream inflammasome signaling components in patients with AOSD indicated a potential pathogenic role of B19‑NS1. Thus, B19‑NS1 may induce expression of IL‑1β and IL‑18 through activation of caspase‑1‑associated NLRP3‑inflammasome in AOSD.

Urate crystals directly activate the T-cell receptor complex and induce T-cell proliferation

Uric acid is a known danger associated molecular pattern molecule able to induce inflammation following internalization of its crystals by cells of the innate immune system. By activating antigen-presenting cells, urate boosts adaptive immunity as well. Furthermore, urate crystals can induce proliferation of isolated T-cells, which are unable to phagocytose crystal particles. In light of the evidence that urate crystals can also activate dendritic cells and macrophages without prior internalization but through sequestration of lipid rafts (and consequently receptors clustering in a non specific manner), the authors evaluated whether such a mechanism is involved in the direct activation of T-cells by urate crystals. In the present study, isolated human T-cells were cultured with or without urate at a concentration above its crystallization level. The expression and phosphorylation state of the T-cell receptor (TCR) complex zeta chain and the expression of the master regulator of cell proliferation c-Myc were assessed by western blotting. T-cell proliferation was measured by bromodeoxyuridine assay. Collectively, the results indicated that urate increased zeta chain phosphorylation indicating that it induces activation of TCR complex directly, since zeta chain phosphorylation takes place at the cell membrane and is a very proximal event in TCR complex-mediated signal transduction. In parallel, urate increased the expression of the transcription factor c-Myc and induced T-cell proliferation. In conclusion, urate crystals directly activate the TCR complex and induce T-cell proliferation.

Physiological functions and pathogenic potential of uric acid: A review

Uric acid is synthesized mainly in the liver, intestines and the vascular endothelium as the end product of an exogenous pool of purines, and endogenously from damaged, dying and dead cells, whereby nucleic acids, adenine and guanine, are degraded into uric acid. Mentioning uric acid generates dread because it is the established etiological agent of the severe, acute and chronic inflammatory arthritis, gout and is implicated in the initiation and progress of the metabolic syndrome. Yet, uric acid is the predominant anti-oxidant molecule in plasma and is necessary and sufficient for induction of type 2 immune responses. These properties may explain its protective potential in neurological and infectious diseases, mainly schistosomiasis. The pivotal protective potential of uric acid against blood-borne pathogens and neurological and autoimmune diseases is yet to be established.

Macrophage-derived IL-1β enhances monosodium urate crystal-triggered NET formation

OBJECTIVE AND DESIGN

Arthritic gout is caused by joint inflammation triggered by the damaging effects of monosodium uric acid (MSU) crystal accumulation in the synovial space. Neutrophils play a major role in mediating joint inflammation in gout. Along with neutrophils, other immune cells, such as macrophages, are present in inflamed joints and contribute to gout pathogenesis. Neutrophils form neutrophil extracellular traps (NETs) in response to MSU crystals. In the presence of MSU crystals, macrophages release IL-1β, a cytokine crucial to initiate gout pathogenesis and neutrophil recruitment. Our research investigated interactions between human macrophages and neutrophils in an in vitro model system and asked how macrophages affect NET formation stimulated by MSU crystals.

MATERIALS OR SUBJECTS

Human neutrophils and PBMCs were isolated from peripheral blood of healthy volunteers. PBMCs were differentiated into macrophages in vitro using human M-CSF.

TREATMENT

Human neutrophils were pretreated with macrophage-conditioned media, neutrophil-conditioned media, recombinant human IL-1β or anakinra prior to stimulation by MSU crystals.

METHOD

Interaction of neutrophils with MSU crystals was evaluated by live imaging using confocal microscopy. The presence of myeloperoxidase (MPO) and neutrophil elastase (NE) was measured by ELISA. NET formation was quantitated by Sytox Orange-based extracellular DNA release assay and NE-DNA ELISA. AggNET formation was assessed by macroscopic evaluation.

RESULTS

We found that crystal- and cell-free supernatants of macrophages stimulated with MSU crystals promote MSU crystal-stimulated NET formation in human neutrophils. This observation was confirmed by additional assays measuring the release of MPO, NE, and the enzymatic activity of NE. MSU crystal-induced NET formation remained unchanged when neutrophil supernatants were tested. IL-1β is a crucial cytokine orchestrating the onset of inflammation in gout and is known to be released in large amounts from macrophages following MSU crystal stimulation. We found that recombinant IL-1β strongly promoted MSU crystal-induced NET formation in human neutrophils. Interestingly, IL-1β alone did not induce any NET release. We also found that clinical grade anakinra, an IL-1 receptor blocker, strongly reduced the NETosis-enhancing effect of macrophage supernatants indicating that IL-1β is mainly responsible for this effect.

CONCLUSIONS

Macrophage-derived IL-1β enhances MSU crystal-induced NET release in neutrophils. We identified a new mechanism by which macrophages and IL-1β affect neutrophil functions, and could contribute to the inflammatory conditions present in gout. Our results also revealed a new anti-inflammatory mechanism of anakinra.

How neutrophil extracellular traps orchestrate the local immune response in gout

Neutrophil granulocytes possess a large arsenal of pro-inflammatory substances and mechanisms that empower them to drive local acute immune reactions to invading microorganisms or endogenous inflammatory triggers. The use of this armory needs to be tightly controlled to avoid chronic inflammation and collateral tissue damage. In gout, inflammation arises from precipitation of uric acid in the form of needle-shaped monosodium urate crystals. Inflammasome activation by these crystals in local immune cells results in a rapid and dramatic recruitment of neutrophils. This neutrophil influx is accompanied by the infamously intense clinical symptoms of inflammation during an acute gout attack. Neutrophilic inflammation however is equipped with a built-in safeguard; activated neutrophils form neutrophil extracellular traps (NETs). At the very high neutrophil densities that occur at the site of inflammation, NETs build aggregates that densely pack the monosodium urate (MSU) crystals and trap and degrade pro-inflammatory mediators by inherent proteases. Local removal of cytokines and chemokines by aggregated NETs explains how acute inflammation can stop in the consistent presence of the inflammatory trigger. Aggregated NETs resemble early stages of the typical large MSU deposits that constitute the pathognomonic structures of gout, tophi. Although tophi contribute to muscosceletal damage and mortality in patients with chronic gout, they can therefore be considered as a payoff that is necessary to silence the intense inflammatory response during acute gout.

IL-1ß and IL-8 are scavenged by the hexadecylamide derivative of hyaluronic acid: a new mechanism

This study aimed to investigate, using an in vitro model, the mechanisms involved in the effects linked to a novel hexadecylamide derivative of hyaluronic acid (HA), HYADD®4 (HS), on some inflammatory aspects related to the osteoarthritis process. The human leukemic monocytic cell line THP-1 was stimulated with calcium pyrophosphate (CPP) crystals or lipopolysaccaride (LPS) and cultured in the presence of HS or two unmodified HAs (500-730 kDa and >1500 kDa, respectively). The effects of the three HA derivatives were compared by examining the inhibition of IL-1ß and IL-8 release, the phagocytic capacity of THP-1, and HA's physical interference with the cytokines and their biological activity. Adding HS simultaneously with the stimuli led to a marked (nearly 100%) decrease in cytokine release and biological activity with respect to the two unmodified HAs. The effect was not altered when a CD44 function-blocking monoclonal antibody was used. Incubation of the three derivatives with IL-1ß and IL-8 led to a reduced bioavailability of the cytokines in the medium in the presence of HS but not of unmodified HA. This study examines a novel mechanism inhibiting cytokine bioactivity. The HA hexadecylamide derivative was found to suppress, in vitro, the inflammatory response induced by CPP crystals and LPS by reducing the bioavailability of the two cytokines that were analyzed.

Mechanism of action of colchicine in the treatment of gout

PURPOSE

The aims of this article were to systematically review the literature about the mechanism of action of colchicine in the multimodal pathology of acute inflammation associated with gout and to consider the clinical utility of colchicine in other chronic inflammatory diseases.

METHODS

The English-language literature on PubMed was searched for articles published between 1990 and October 2013, with a cross-reference to citations across all years. Relevant articles pertaining to the mechanism of action of colchicine and the clinical applications of colchicine in gout and other inflammatory conditions were identified and reviewed.

FINDINGS

The molecular pathology of acute inflammation associated with gouty arthritis involves several concurrent pathways triggered by a variety of interactions between monosodium urate crystals and the surface of cells. Colchicine modulates multiple pro- and antiinflammatory pathways associated with gouty arthritis. Colchicine prevents microtubule assembly and thereby disrupts inflammasome activation, microtubule-based inflammatory cell chemotaxis, generation of leukotrienes and cytokines, and phagocytosis. Many of these cellular processes can be found in other diseases involving chronic inflammation. The multimodal mechanism of action of colchicine suggests potential efficacy of colchicine in other comorbid conditions associated with gout, such as osteoarthritis and cardiovascular disease.

IMPLICATIONS

Colchicine has multiple mechanisms of action that affect inflammatory processes and result in its utility for treating and preventing acute gout flare. Other chronic inflammatory diseases that invoke these molecular pathways may represent new therapeutic applications for colchicine.

The crystallization of monosodium urate

Gout is a common crystal-induced arthritis, in which monosodium urate (MSU) crystals precipitate within joints and soft tissues and elicit an inflammatory response. The causes of elevated serum urate and the inflammatory pathways activated by MSU crystals have been well studied, but less is known about the processes leading to crystal formation and growth. Uric acid, the final product of purine metabolism, is a weak acid that circulates as the deprotonated urate anion under physiologic conditions, and combines with sodium ions to form MSU. MSU crystals are known to have a triclinic structure, in which stacked sheets of purine rings form the needle-shaped crystals that are observed microscopically. Exposed, charged crystal surfaces are thought to allow for interaction with phospholipid membranes and serum factors, playing a role in the crystal-mediated inflammatory response. While hyperuricemia is a clear risk factor for gout, local factors have been hypothesized to play a role in crystal formation, such as temperature, pH, mechanical stress, cartilage components, and other synovial and serum factors. Interestingly, several studies suggest that MSU crystals may drive the generation of crystal-specific antibodies that facilitate future MSU crystallization. Here, we review MSU crystal biology, including a discussion of crystal structure, effector function, and factors thought to play a role in crystal formation. We also briefly compare MSU biology to that of uric acid stones causing nephrolithasis, and consider the potential treatment implications of MSU crystal biology.

Transfusion-Related Acute Lung Injury: The Work of DAMPs

Current notions in immunology hold that not only pathogen-mediated tissue injury but any injury activates the innate immune system. In principle, this evolutionarily highly conserved, rapid first-line defense system responds to pathogen-induced injury with the creation of infectious inflammation, and non-pathogen-induced tissue injury with 'sterile' tissue inflammation. In this review, evidence has been collected in support of the notion that the transfusion-related acute lung injury induces a 'sterile' inflammation in the lung of transfused patients in terms of an acute innate inflammatory disease. The inflammatory response is mediated by the patient's innate immune cells including lung-passing neutrophils and pulmonary endothelial cells, which are equipped with pattern recognition receptors. These receptors are able to sense injury-induced, damage-associated molecular patterns (DAMPs) generated during collection, processing, and storage of blood/blood components. The recognition process leads to activation of these innate cells. A critical role for a protein complex known as the NLRP3 inflammasome has been suggested to be at the center of such a scenario. This complex undergoes an initial 'priming' step mediated by 1 class of DAMPs and then an 'activating' step mediated by another class of DAMPs to activate interleukin-1beta and interleukin-18. These 2 cytokines then promote, via transactivation, the formation of lung inflammation.