Proline-rich tyrosine kinase 2 and Src kinase signaling transduce monosodium urate crystal-induced nitric oxide production and matrix metalloproteinase 3 expression in chondrocytes

Traditional herbal medicine: Therapeutic potential in acute gouty arthritis

ETHNOPHARMACOLOGICAL RELEVANCE

Acute gouty arthritis (AGA) is characterized by a rapid inflammatory reaction caused by the build-up of monosodium urate (MSU) crystals in the tissues surrounding the joints. This condition often associated with hyperuricemia (HUA), is distinguished by its symptoms of intense pain, active inflammation, and swelling of the joints. Traditional approaches in AGA management often fall short of desired outcomes in clinical settings. However, recent ethnopharmacological investigations have been focusing on the potential of Traditional Herbal Medicine (THM) in various forms, exploring their therapeutic impact and targets in AGA treatment.

AIM OF THE REVIEW

This review briefly summarizes the current potential pharmacological mechanisms of THMs - including active ingredients, extracts, and prescriptions -in the treatment of AGA, and discusses the relevant potential mechanisms and molecular targets in depth. The objective of this study is to offer extensive information and a reference point for the exploration of targeted AGA treatment using THMs.

MATERIALS AND METHODS

This review obtained scientific publications focused on in vitro and in vivo studies of anti-AGA THMs conducted between 2013 and 2023. The literature was collected from various journals and electronic databases, including PubMed, Elsevier, ScienceDirect, Web of Science, and Google Scholar. The retrieval and analysis of relevant articles were guided by keywords such as "acute gouty arthritis and Chinese herbal medicine," "acute gouty arthritis herbal prescription," "acute gouty arthritis and immune cells," "acute gouty arthritis and inflammation," "acute gouty arthritis and NOD-like receptor thermoprotein domain associated protein 3 (NLRP3)," "acute gouty arthritis and miRNA," and "acute gouty arthritis and oxidative stress."

RESULTS

We found that AGA has a large number of therapeutic targets, highlighting the effectiveness the potential of THMs in AGA treatment through in vitro and in vivo studies. THMs and their active ingredients can mitigate AGA symptoms through a variety of therapeutic targets, such as influencing macrophage polarization, neutrophils, T cells, natural killer (NK) cells, and addressing factors like inflammation, NLRP3 inflammasome, signaling pathways, oxidative stress, and miRNA multi-target interactions. The anti-AGA properties of THMs, including their active components and prescriptions, were systematically summarized and categorized based on their respective therapeutic targets.

CONCLUSION

phenolic, flavonoid, terpenoid and alkaloid compounds in THMs are considered the key ingredients to improve AGA. THMs and their active ingredients achieve enhanced efficacy through interactions with multiple targets, of which NLRP3 is a main therapeutic target. Nonetheless, given the intricate composition of traditional Chinese medicine (TCM), additional research is required to unravel the underlying mechanisms and molecular targets through which THMs alleviate AGA.

Local delivery of gaseous signaling molecules for orthopedic disease therapy

Over the past decade, a proliferation of research has used nanoparticles to deliver gaseous signaling molecules for medical purposes. The discovery and revelation of the role of gaseous signaling molecules have been accompanied by nanoparticle therapies for their local delivery. While most of them have been applied in oncology, recent advances have demonstrated their considerable potential in diagnosing and treating orthopedic diseases. Three of the currently recognized gaseous signaling molecules, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), are highlighted in this review along with their distinctive biological functions and roles in orthopedic diseases. Moreover, this review summarizes the progress in therapeutic development over the past ten years with a deeper discussion of unresolved issues and potential clinical applications.

A brief review on in vivo models for Gouty Arthritis

Gout is more common in men than in women, by a factor of 3.1–10.1. Gout prevalence and incidence have increased in recent decades, with prevalence reaching 11–13% and incidence reaching 0.4% in people over the age of 80. Age-related renal impairment, altered drug distribution, and increased prevalence of comorbidities have significant consequences for safe and effective gout pharmacotherapy. The Discovery of Fruitful in-vivo animal models needs the effective screening of drugs or formulations used in the treatment of gout. In vivo animal models of Gouty arthritis are extensively used to investigate pathogenic mechanisms governing inflammation-driven bone and cartilage damage. Four commonly utilized models include the Potassium oxonate induced hyperuricemic model, MSU crystals induced gouty arthritis animal model, Animal Model of Acute Gouty Arthritis with Hyperuricemia, and Diet-induced hyperuricemia. These offer unique advantages for correlating different aspects of gouty arthritis with human disease. In-vivo animal models served as testing beds for novel biological therapies, including cytokine blockers and small molecule inhibitors of intracellular signaling that have revolutionized gouty arthritis treatment. This review highlights a brief overview of in vivo experimental models for assessment of hypouricemic, anti-inflammatory, as well as renal protective effects of test compounds with some evaluation parameters in detail.

Pathophysiology of Gout

Multiple interacting checkpoints are involved in the pathophysiology of gout. Hyperuricemia is the key risk factor for gout and is considered a prerequisite for monosodium urate (MSU) crystal formation. Urate underexcretion through renal and gut mechanisms is the major mechanism for hyperuricemia in most people. Multiple genetic, environmental, and metabolic factors are associated with serum urate and alter urate transport or synthesis. Urate supersaturation is the most important factor for MSU crystal formation, and other factors such as temperature, pH, and connective tissue components also play a role. The nucleotide-binding oligomerization domain leucine-rich repeats and pyrin domain-containing protein 3 inflammasome plays a pivotal role in the inflammatory response to MSU crystals, and interleukin 1β is the key cytokine mediating the inflammatory cascade. Variations in the regulatory mechanisms of this inflammatory response may affect an individual's susceptibility to developing gout. Tophus formation is the cardinal feature of advanced gout, and both MSU crystals and the inflammatory tissue component of the tophus contribute to the development of structural joint damage owing to gout. In this article, we review the pathophysiologic mechanisms of hyperuricemia, MSU crystal formation and the associated inflammatory response, tophus formation, and structural joint damage in gout.

Suppression of monosodium urate crystal-induced inflammation by inhibiting TGF-β-activated kinase 1-dependent signaling: role of the ubiquitin proteasome system

Monosodium urate (MSU) crystals activate inflammatory pathways that overlap with interleukin-1β (IL-1β) signaling. However, the post-translational mechanisms involved and the role of signaling proteins in this activation are unknown. In the present study, we investigated the intracellular signaling mechanisms involved in MSU-induced activation of THP-1 macrophages and human nondiseased synovial fibroblasts (NLSFs) and the in vivo efficacy of an inhibitor of tumor growth factor-β (TGF-β)-activated kinase 1 (TAK1), 5Z-7-oxozeaenol, in MSU-induced paw inflammation in C57BL/6 mice. THP-1 macrophage activation with MSU crystals (25-200 µg/ml) resulted in the rapid and sustained phosphorylation of interleukin-1 receptor-activated kinase 1 (IRAK1 Thr209) and TAK1 (Thr184/187) and their association with the E3 ubiquitin ligase TRAF6. At the cellular level, MSU inhibited the deubiquitinases A20 and UCHL2 and increased 20s proteasomal activity, leading to a global decrease in K63-linked ubiquitination and increase in K48-linked ubiquitination in THP-1 macrophages. While MSU did not stimulate cytokine production in NLSFs, it significantly amplified IL-1β-induced IL-6, IL-8, and ENA-78/CXCL5 production. Docking studies and MD simulations followed by TAK1 in vitro kinase assays revealed that uric acid molecules are capable of arresting TAK1 in an active-state conformation, resulting in sustained TAK1 kinase activation. Importantly, MSU-induced proinflammatory cytokine production was completely inhibited by 5Z-7-oxozeaenol but not IRAK1/4 or TRAF6 inhibitors. Administration of 5Z-7-oxozeaenol (5 or 15 mg/kg; orally) significantly inhibited MSU-induced paw inflammation in C57BL/6 mice. Our study identifies a novel post-translational mechanism of TAK1 activation by MSU and suggests the therapeutic potential of TAK1 in regulating MSU-induced inflammation.

Urate and osteoarthritis: Evidence for a reciprocal relationship

Hyperuricemia is a common condition, and in a subset of patients leads to gout, the most common inflammatory arthritis. Osteoarthritis is the most common form of arthritis overall, and gout and osteoarthritis frequently coexist in the same patient. However, the relationship between the two remains poorly defined. More particularly, the impact of osteoarthritis on the development of gout, and the impact of gout on the development of osteoarthritis, remain to be determined. Additionally, whether hyperuricemia mediates osteoarthritis in the absence of gout is uncertain. Here, we review the evidence linking gout and osteoarthritis, with a special focus on the role of hyperuricemia in the presence or absence of gout. Since disease modifying agents are currently available for hyperuricemia and gout but not for osteoarthritis, a contributory role for urate in the pathogenesis of osteoarthritis could have important clinical implications.

Urate transport capacity of glucose transporter 9 and urate transporter 1 in cartilage chondrocytes

Chronic gouty arthritis, caused by a persistent increase in, and the deposition of, soluble uric acid (sUA), can induce pathological chondrocyte destruction; however, the effects of urate transport and intracellular sUA on chondrocyte functionality and viability are yet to be fully determined. Thus, the aim of the present study was to investigate the presence and functionality of a urate transport system in chondrocytes. The expression profiles of two primary urate reabsorptive transporters, glucose transporter 9 (GLUT9) and urate transporter 1 (URAT1), in human articular cartilage and chondrocyte cell lines were examined via western blotting, reverse transcription-quantitative PCR, immunohistochemistry and immunofluorescence. Then, chondrocytes were incubated with exogenous sUA at increasing concentrations. Negative control assays were conducted via the specific knockdown of GLUT9 and URAT1 with lentiviral short hairpin (sh)RNAs, and by pretreatment with benzbromarone, a known inhibitor of the two transporters. Intracellular UA concentrations were measured using colorimetric assays. The expression levels of GLUT9 and URAT1 were determined in cartilage tissues and chondrocyte cell lines. Incubation of chondrocytes with sUA led to a concentration-dependent increase in intracellular urate concentrations, which was inhibited by GLUT9 or URAT1 knockdown, or by benzbromarone pretreatment (27.13±2.70, 44.22±2.34 and 58.46±2.32% reduction, respectively). In particular, benzbromarone further decreased the already-reduced intracellular UA concentrations in HC-shGLUT9 and HC-shURAT1 cells by 46.79±2.46 and 39.79±2.22%, respectively. Cells overexpressing GLUT9 and URAT1 were used as the positive cell control, which showed increased intracellular UA concentrations that could be reversed by treatment with benzbromarone. In conclusion, chondrocytes may possess an active UA transport system. GLUT9 and URAT1 functioned synergistically to transport UA into the chondrocyte cytoplasm, which was inhibited by specific gene knockdowns and drug-induced inhibition. These results may be fundamental in the further investigation of the pathological changes to chondrocytes induced by sUA during gouty arthritis, and identified UA transport processes as potential targets for the early control of chronic gouty arthritis.

Anti-inflammatory effects of traditional mixed extract of medicinal herbs (MEMH) on monosodium urate crystal-induced gouty arthritis

Korean oriental medicine prescription is widely used for the treatment of gouty diseases. In the present study, we investigated anti-inflammatory effects of modified Korean herbal formulation, mixed extract of medicinal herbs (MEMH), and its modulatory effects on inflammatory mediators associated with gouty arthritis. Both in vitro and in vivo studies were carried out to assess the anti-inflammatory efficacy of MEMH on monosodium urate (MSU) crystals-induced gouty inflammation. MSU crystals stimulated human chondrosarcoma cell line, SW1353, and human primary chondrocytes were treated with MEMH in vitro. The expression levels of pro-inflammatory mediators and metalloproteases were analyzed. The effect of MEMH on NFκB signaling pathway in SW1353 cells was examined. Effect of MEMH on the mRNA expression level of pro-inflammatory mediators and chemotactic factor from human monocytic cell line, THP-1, was also analyzed. The probable role of MEMH in the differentiation process of osteoblast like cells, SaOS-2, after MSU treatment was also observed. To investigate the effects of MEMH in vivo, MSU crystals-induced ankle arthritic model was established. Histopathological changes in affected joints and plasma levels of pro-inflammatory mediators (IL-1β and TNFα) were recorded. MEMH inhibited NFκB signaling pathway and COX-2 protein expression in chondrocytes. MSU-induced mRNA expressions of pro-inflammatory mediators and chemotactic cytokines were suppressed by MEMH. In MSU crystals-induced ankle arthritic mouse model, administration of MEMH relieved inflammatory symptoms and decreased the plasma levels of IL-1β and TNFα. The results indicated that MEMH can effectively inhibit the expression of inflammatory mediators in gouty arthritis, demonstrating its potential for treating gouty arthritis.

Disease-Associated Particulates and Joint Inflammation; Mechanistic Insights and Potential Therapeutic Targets

It is now well established that intra-articular deposition of endogenous particulates, such as osteoarthritis-associated basic calcium phosphate crystals, gout-associated monosodium urate crystals, and calcium deposition disease-associated calcium pyrophosphate crystals, contributes to joint destruction through the production of cartilage-degrading enzymes and pro-inflammatory cytokines. Furthermore, exogenous wear-debris particles, generated from prosthetic implants, drive periprosthetic osteolysis which impacts on the longevity of total joint replacements. Over the last few years, significant insight has been gained into the mechanisms through which these particulates exert their effects. Not only has this increased our understanding of the pathological processes associated with crystal deposition but it has also led to the identification of a number of therapeutic targets to treat particulate-associated disease. In this review, we discuss recent developments regarding the cellular events triggered by joint-associated particulates, as well as future directions in therapy for particulate-related arthropathies.

Xanthine oxidoreductase is required for genotoxic stress-induced NKG2D ligand expression and gemcitabine-mediated antitumor activity

MICA/B (the major histocompatibility antigen-related chain A and B) and Rae I are stress-inducible ligands for the immune-receptor NKG2D. Mechanisms by which genotoxic stress and DNA damage induce the expression of NKG2D ligands remain incompletely understood. Here, we report that inhibition of xanthine oxidoreductase (XOR) activity by allopurinol or inhibition of XOR expression by gene knockdown abrogated genotoxic stress-induced expression of MICA/B and Rae I in three tumor cell lines. XOR knockdown also blocked gemcitabine-mediated antitumor activity in an orthotopic syngeneic mouse model of breast cancer. As a rate-limiting enzyme in the purine catabolic pathway, XOR generates two end-products, uric acid and reactive oxygen species (ROS). ROS scavenging had an insignificant effect on genotoxic drug-induced MICA/B expression but modestly inhibited radiation-induced MICA/B expression. Exogenous uric acid (in the form of monosodium urate) induced MICA/B expression by activating the MAP kinase pathway. Allopurinol blocked genotoxic stress-induced MAP kinase activation. Our study provides mechanistic insights into genotoxic stress-induced activation of the MAP kinase pathway and suggests that XOR is required for genotoxic stress-induced NKG2D ligand expression and gemcitabine-mediated antitumor activity.

Gout and Osteoarthritis: Associations, Pathophysiology, and Therapeutic Implications

Osteoarthritis (OA), the most common type of arthritis worldwide, is a degenerative disease of diarthrodial joints resulting in pain, reduced quality of life, and socioeconomic burden. Gout, the most common form of inflammatory arthritis, is a consequence of persistently elevated levels of urate and the formation of proinflammatory monosodium urate crystals in joints. Clinicians have long noted a predilection for both diseases to occur in the same joints. In this review, we provide an overview into research elucidating possible biochemical, mechanical, and immunological relationships between gout and OA. We additionally consider the potential implications of these relationships for OA treatment.

Intra-articular basic calcium phosphate and monosodium urate crystals inhibit anti-osteoclastogenic cytokine signalling

OBJECTIVE

Basic calcium phosphate (BCP) and monosodium urate (MSU) crystals are particulates with potent pro-inflammatory effects, associated with osteoarthritis (OA) and gout, respectively. Bone erosion, due to increased osteoclastogenesis, is a hallmark of both arthropathies and results in severe joint destruction. The aim of this study was to investigate the effect of these endogenous particulates on anti-osteoclastogenic cytokine signalling.

METHODS

Human osteoclast precursors (OcP) were treated with BCP and MSU crystals prior to stimulation with Interleukin (IL-6) or Interferon (IFN-γ) and the effect on Signal Transducer and Activator of Transcription (STAT)-3 and STAT-1 activation in addition to Mitogen Activated Protein Kinase (MAPK) activation was examined by immunoblotting. Crystal-induced suppressor of cytokine signalling (SOCS) protein and SH-2 containing tyrosine phosphatase (SHP) expression was assessed by real-time polymerase chain reaction (PCR) in the presence and absence of MAPK inhibitors.

RESULTS

Pre-treatment with BCP or MSU crystals for 1 h inhibited IL-6-induced STAT-3 activation in human OcP, while pre-treatment for 3 h inhibited IFN-γ-induced STAT-1 activation. Both crystals activated p38 and extracellular signal-regulated (ERK) MAPKs with BCP crystals also activating c-Jun N-terminal kinase (JNK). Inhibition of p38 counteracted the inhibitory effect of BCP and MSU crystals and restored STAT-3 phosphorylation. In contrast, STAT-1 phosphorylation was not restored by MAPK inhibition. Finally, both crystals potently induced the expression of SOCS-3 in a MAPK dependent manner, while BCP crystals also induced expression of SHP-1 and SHP-2.

CONCLUSION

This study provides further insight into the pathogenic effects of endogenous particulates in joint arthropathies and demonstrates how they may contribute to bone erosion via the inhibition of anti-osteoclastogenic cytokine signalling. Potential targets to overcome these effects include p38 MAPK, SOCS-3 and SHP phosphatases.

Relationship of bone erosion with the urate and soft tissue components of the tophus in gout: a dual energy computed tomography study

OBJECTIVES

Imaging and pathology studies have established a close relationship between tophus and bone erosion in gout. The tophus is an organized structure consisting of urate crystals and chronic inflammatory tissue. The aim of this work was to examine the relationship between bone erosion and each component of the tophus.

METHODS

Plain radiographs and dual energy CT scans of the feet were prospectively obtained from 92 people with tophaceous gout. The 10 MTP joints were scored for erosion score, tophus urate and soft tissue volume. Data were analysed using generalized estimating equations and mediation analysis.

RESULTS

Tophus was visualized in 80.2% of all joints with radiographic (XR) erosion [odds ratio (OR) = 7.1 (95% CI: 4.8, 10.6)] and urate was visualized in 78.6% of all joints with XR erosion [OR = 6.6 (95% CI: 4.7, 9.3)]. In mediation analysis, tophus urate volume and soft tissue volume were directly associated with XR erosion score. About a third of the association of the tophus urate volume with XR erosion score was indirectly mediated through the strong association between tophus urate volume and tophus soft tissue volume.

CONCLUSION

Urate and soft tissue components of the tophus are strongly and independently associated with bone erosion in gout.

Traditional Chinese Medicine Formula "Xiaofeng granules" suppressed gouty arthritis animal models and inhibited the proteoglycan degradation on chondrocytes induced by monosodium urate

ETHNOPHARMACOLOGICAL RELEVANCE

Xiaofeng Granules (XF) is a kind of granules prepared by the famous traditional Chinese medicine formula for its efficiency in treating gouty diseases.

AIM OF THE STUDY

We investigated the relevance between XF that made from Modified simiaowan (MSW) as the anti-gouty arthritis drugs and protective mechanisms for cartilage matrix in order to provide the evidence for new drug application.

MATERIALS AND METHODS

In the present study, we evaluated the anti-gouty arthritis activity of XF in rats and rabbits models induced by MSU together with chondrocytes focusing on the link to proteoglycan degradation in vitro studies.

RESULTS

The results demonstrated that XF significantly reduced the swelling rate and attenuated the pathological changes in joints. The XF-containing serum were used medicated serum in cellular experiments. The in vitro data were in accordance with the in vivo results, showing that the constituents in XF-containing serum had obvious inhibitory effects on the activation of pro-inflammatory mediators in chondrocytes. Moreover, XF-containing serum substantially inhibited MSU-induced expression of glycosaminoglycans(GAG) and hydroxyproline(Hyp), and up regulated proteoglycan, which might be associated with the regulation of the balance of MMP-3/TIMP-1and ADAMTS-4/TIMP-3 inchondrocytes.

CONCLUSION

In conclusion, XF that made from MSW showed obvious effects on acute gouty arthritis, which also provided an effective protection on cartilage matrix degradation.

Factors associated with change in radiographic damage scores in gout: a prospective observational study

BACKGROUND/AIMS

Radiographic damage is frequently observed in patients with longstanding gout. The aim of this prospective observational study was to determine factors associated with change in radiographic damage scores in gout.

METHODS

People with gout and disease duration <10 years were recruited into this prospective observational study. At the baseline visit, structured assessment was undertaken in 290 participants including detailed clinical examination and plain radiographs (XR) of the hands and feet. Participants were invited to attend a further study visit with repeat XR 3 years after the baseline visit. XR were scored for erosion and joint space narrowing according to the gout-modified Sharp/van der Heijde XR damage score.

RESULTS

Age, subcutaneous tophus count and tender joint count were independently associated with XR damage score at the baseline visit. Paired serial XR were available for 140 participants. In stepwise linear regression analysis, change in total damage score over 3 years was positively associated with change in subcutaneous tophus count and baseline XR damage score, and inversely associated with baseline subcutaneous tophus count (model R²=0.39, p<0.001). Change in subcutaneous tophus count contributed most to the change in erosion score (partial R² change=0.31, p<0.001), and baseline XR damage score contributed most to the change in narrowing score (partial R² change=0.31, p<0.001).

CONCLUSIONS

Development of new subcutaneous tophi and baseline radiographic damage are associated with progressive joint damage scores in people with gout. These data provide further evidence that the tophus plays a central role in bone erosion in gout.

Morin, a Bioflavonoid Suppresses Monosodium Urate Crystal-Induced Inflammatory Immune Response in RAW 264.7 Macrophages through the Inhibition of Inflammatory Mediators, Intracellular ROS Levels and NF-κB Activation

Our previous studies had reported that morin, a bioflavanoid exhibited potent anti-inflammatory effect against adjuvant-induced arthritic rats. In this current study, we investigated the anti-inflammatory mechanism of morin against monosodium urate crystal (MSU)-induced inflammation in RAW 264.7 macrophage cells, an in vitro model for acute gouty arthritis. For comparison purpose, colchicine was used as a reference drug. We have observed that morin (100–300 μM) treatment significantly suppressed the levels of inflammatory cytokines (TNF-α, IL-1β, IL-6, MCP-1 and VEGF), inflammatory mediators (NO and PEG₂), and lysosomal enzymes (acid phosphatase, β-galactosidase, N-acetyl glucosamindase and cathepsin D) in MSU-crystals stimulated macrophage cells. The mRNA expression of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and MCP-1), inflammatory enzymes (iNOS and COX-2), and NF-κBp65 was found downregulated in MSU crystal stimulated macrophage cells by morin treatment, however, the mRNA expression of hypoxanthine phospho ribosyl transferse (HPRT) was found to be increased. The flow cytometry analysis revealed that morin treatment decreased intracellular reactive oxygen species levels in MSU crystal stimulated macrophage cells. The western blot analysis clearly showed that morin mainly exerts its anti-inflammatory effects by inhibiting the MSU crystal-induced COX-2 and TNF-α protein expression through the inactivation of NF-κB signaling pathway in RAW 264.7 macrophage cells similar to that of BAY 11–7082 (IκB kinase inhibitor). Our results collectively suggest that morin can be a potential therapeutic agent for inflammatory disorders like acute gouty arthritis.

Monosodium Urate Crystal-Induced Chondrocyte Death via Autophagic Process

Monosodium urate (MSU) crystals, which are highly precipitated in the joint cartilage, increase the production of cartilage-degrading enzymes and pro-inflammatory mediators in cartilage, thereby leading to gouty inflammation and joint damage. In this study, we investigated the effect of MSU crystals on the viability of human articular chondrocytes and the mechanism of MSU crystal-induced chondrocyte death. MSU crystals significantly decreased the viability of primary chondrocytes in a time- and dose-dependent manner. DNA fragmentation was observed in a culture medium of MSU crystal-treated chondrocytes, but not in cell lysates. MSU crystals did not activate caspase-3, a marker of apoptosis, compared with actinomycin D and TNF-α-treated cells. MSU crystals did not directly affect the expression of endoplasmic reticulum (ER) stress markers at the mRNA and protein levels. However, MSU crystals significantly increased the LC3-II level in a time-dependent manner, indicating autophagy activation. Moreover, MSU crystal-induced autophagy and subsequent chondrocyte death were significantly inhibited by 3-methyladenine, a blocker of autophagosomes formation. MSU crystals activated autophagy via inhibition of phosporylation of the Akt/mTOR signaling pathway. These results demonstrate that MSU crystals may cause the death of chondrocytes through the activation of the autophagic process rather than apoptosis or ER stress.

Lemnalol attenuates mast cell activation and osteoclast activity in a gouty arthritis model

OBJECTIVES

In this study, we investigated the effects of a soft coral-derived anti-inflammatory compound, lemnalol, on mast cell (MC) function and osteoclast activity in rats with monosodium urate (MSU) crystal-induced gouty arthritis.

METHODS

In this study, we examined the therapeutic effects of lemnalol on intra-articular injection of MSU induces gouty arthritis with the measurement of ankle oedema. Toluidine blue staining were used to analyse the infiltration and the percentage degranulation MCs. Immunohistochemical analysis showed CD117, transforming growth factor beta 1 (TGF-β1), matrix metalloproteinase 9 (MMP-9), the osteoclast markers cathepsin K and tartrate-resistant acid phosphatase (TRAP) protein expression in ankle tissue.

KEY FINDINGS

We found that both infiltration and degranulation of MCs increased at 24 h after MSU injection in the ankle joint. Immunohistochemical analysis showed that MSU induced upregulation of TGF-β1, MMP-9, the osteoclast markers cathepsin K and TRAP in ankle tissues. Administration of lemnalol ameliorated MSU-induced TGF-β1, MMP-9, cathepsin K and TRAP protein expression.

CONCLUSIONS

Taken together, our results show that MSU-induced gouty arthritis is accompanied by osteoclast-related protein upregulation and that lemnalol treatment may be beneficial for the attenuation of MC infiltration and degranulation and for suppressing osteoclast activation in gouty arthritis.

Exploratory study of radiographic change in patients with tophaceous gout treated with intensive urate-lowering therapy

OBJECTIVE

Tophi are strongly associated with structural damage in gout, and urate-lowering therapy reduces tophus size. Pegloticase leads to dramatic reductions in serum urate and subcutaneous tophi in treatment responders. The aim of this analysis was to examine whether profound urate lowering can alter radiographic findings in gout.

METHODS

Serial plain radiographs of the hands and feet were obtained from 8 patients with tophaceous gout treated with pegloticase. Radiographs were scored for erosion and joint space narrowing (JSN) according to the gout-modified Sharp/van der Heijde method. Scorers were blinded to each other's scores and to the clinical characteristics of the patients (including the clinical response to pegloticase). A detailed qualitative site-by-site analysis was undertaken to define additional changes observed from baseline.

RESULTS

All patients experienced a profound urate-lowering response (serum urate level <1 mg/dl) during pegloticase treatment. For the entire group, the median total radiographic scores reduced from 69.25 (range 1.5-138) at baseline to 57.25 (range 1.5-110) at 12 months (P = 0.02). Median erosion scores reduced over 1 year (P = 0.008), but JSN scores did not change (P = 0.50). Further reductions were observed in total scores and erosion scores in 5 patients with 24-month followup films (one-way analysis of variance P = 0.009 for total score, 0.02 for erosion, and 0.95 for JSN). Qualitative site-by-site analysis identified regression of soft tissue masses, increased sclerosis, and filling in of erosions in the followup films.

CONCLUSION

This exploratory study suggests that profound urate lowering can lead to improvement in structural damage, particularly bone erosion, in patients with tophaceous gout.

Relationship between structural joint damage and urate deposition in gout: a plain radiography and dual-energy CT study

Objectives

The aim of this work was to examine the relationship between joint damage and monosodium urate (MSU) crystal deposition in gout.

Methods

Plain radiographs and dual-energy CT (DECT) scans of the feet were prospectively obtained from 92 people with tophaceous gout. Subcutaneous tophus count was recorded. The ten metatarsophalangeal joints were scored on plain radiography for Sharp–van der Heijde erosion and joint space narrowing (JSN) scores, and presence of spur, osteophyte, periosteal new bone and sclerosis (920 total joints). DECT scans were analysed for the presence of MSU crystal deposition at the same joints.

Results

DECT MSU crystal deposition was more frequently observed in joints with erosion (OR (95% CI) 8.5 (5.5 to 13.1)), JSN (4.2 (2.7 to 6.7%)), spur (7.9 (4.9 to 12.8)), osteophyte (3.9 (2.5 to 6.0)), periosteal new bone (7.0 (4.0 to 12.2)) and sclerosis (6.9 (4.6 to 10.2)), p<0.0001 for all. A strong linear relationship was observed in the frequency of joints affected by MSU crystals with radiographic erosion score (p<0.0001). The number of joints at each site with MSU crystal deposition correlated with all features of radiographic joint damage (r>0.88, p<0.05 for all). In linear regression models, the relationship between MSU crystal deposition and all radiographic changes except JSN and osteophytes persisted after adjusting for subcutaneous tophus count, serum urate concentration and disease duration.

Conclusions

MSU crystals are frequently present in joints affected by radiographic damage in gout. These findings support the concept that MSU crystals interact with articular tissues to influence the development of structural joint damage in this disease.

Immunopathological effects of malaria pigment or hemozoin and other crystals

Blood-stage malaria parasites produce insoluble hemozoin (Hz) crystals that are released in the blood circulation upon schizont rupture. In general, endogenous crystal formation or inhalation of crystalline materials is often associated with pathology. As the immune system responds differently to crystalline particles than to soluble molecules, in this review, the properties, immunological recognition, and pathogenic responses of Hz are discussed, and compared with two other major pathogenic crystals, monosodium urate (MSU) and asbestos. Because of the size and shape of MSU crystals and asbestos fibers, phagolysosomal formation is inefficient and often results in leakage of lysosomal content in the cell cytoplasm and/or in the extracellular environment with subsequent cell damage and cell death. Phagolysosomal formation after Hz ingestion is normal, but Hz remains stored inside these cells for months or even longer without any detectable degradation. Nonetheless, the different types of crystals are recognized by similar immune receptors, involving Toll-like receptors, the inflammasome, antibodies, and/or complement factors, and through similar signaling cascades, they activate both proinflammatory and anti-inflammatory immune responses that contribute to inflammation-associated pathology.

The Effects of Monosodium Urate Monohydrate Crystals on Chondrocyte Viability and Function: Implications for Development of Cartilage Damage in Gout

Objective.

Cartilage damage is frequently observed in advanced destructive gout. The aim of our study was to investigate the effects of monosodium urate monohydrate (MSU) crystals on chondrocyte viability and function.

Methods.

The alamarBlue assay and flow cytometry were used to assess the viability of primary human chondrocytes and cartilage explants following culture with MSU crystals. The number of dead chondrocytes in cartilage explants cultured with MSU crystals was quantified. Real-time PCR was used to determine changes in the relative mRNA expression levels of chondrocytic genes. The histological appearance of cartilage in joints affected by gout was also examined.

Results.

MSU crystals rapidly reduced primary human chondrocyte and cartilage explant viability in a dose-dependent manner (p < 0.01 for both). Cartilage explants cultured with MSU crystals had a greater percentage of dead chondrocytes at the articular surface compared to untreated cartilage (p = 0.004). Relative mRNA expression of type II collagen and the cartilage matrix proteins aggrecan and versican was decreased in chondrocytes following culture with MSU crystals (p < 0.05 for all). However, expression of the degradative enzymes ADAMTS4 and ADAMTS5 was increased (p < 0.05 for both). In joints affected by gout, normal cartilage architecture was lost, with empty chondrocyte lacunae observed.

Conclusion.

MSU crystals have profound inhibitory effects on chondrocyte viability and function. Interactions between MSU crystals and chondrocytes may contribute to cartilage damage in gout through reduction of chondrocyte viability and promotion of a catabolic state.

Linked decreases in liver kinase B1 and AMP-activated protein kinase activity modulate matrix catabolic responses to biomechanical injury in chondrocytes

Introduction

AMP-activated protein kinase (AMPK) maintains cultured chondrocyte matrix homeostasis in response to inflammatory cytokines. AMPK activity is decreased in human knee osteoarthritis (OA) chondrocytes. Liver kinase B1 (LKB1) is one of the upstream activators of AMPK. Hence, we examined the relationship between LKB1 and AMPK activity in OA and aging cartilages, and in chondrocytes subjected to inflammatory cytokine treatment and biomechanical compression injury, and performed translational studies of AMPK pharmacologic activation.

Methods

We assessed activity (phosphorylation) of LKB1 and AMPKα in mouse knee OA cartilage, in aging mouse cartilage (6 to 24 months), and in chondrocytes after mechanical injury by dynamic compression, via immunohistochemistry or western blot. We knocked down LKB1 by siRNA transfection. Nitric oxide, matrix metalloproteinase (MMP)-3, and MMP-13 release were measured by Griess reaction and ELISA, respectively.

Results

Knockdown of LKB1 attenuated chondrocyte AMPK activity, and increased nitric oxide, MMP-3 and MMP-13 release (P <0.05) in response to IL-1β and TNFα. Both LKB1 and AMPK activity were decreased in mouse knee OA and aged knee cartilage, and in bovine chondrocytes after biomechanical injury. Pretreatment of bovine chondrocytes with AMPK activators AICAR and A-769662 inhibited both AMPKα dephosphorylation and catabolic responses after biomechanical injury.

Conclusion

LKB1 is required for chondrocyte AMPK activity, thereby inhibiting matrix catabolic responses to inflammatory cytokines. Concurrent loss of LKB1 and AMPK activity in articular chondrocytes is associated with OA, aging and biomechanical injury. Conversely, pharmacologic AMPK activation attenuates catabolic responses to biomechanical injury, suggesting a potentially novel approach to inhibit OA development and progression.

PYK2: a calcium-sensitive protein tyrosine kinase activated in response to fertilization of the zebrafish oocyte

Fertilization begins with binding and fusion of a sperm with the oocyte, a process that triggers a high amplitude calcium transient which propagates through the oocyte and stimulates a series of preprogrammed signal transduction events critical for zygote development. Identification of the pathways downstream of this calcium transient remains an important step in understanding the basis of zygote quality. The present study demonstrates that the calcium-calmodulin sensitive protein tyrosine kinase PYK2 is a target of the fertilization-induced calcium transient in the zebrafish oocyte and that it plays an important role in actin-mediated events critical for sperm incorporation. At fertilization, PYK2 was activated initially at the site of sperm-oocyte interaction and was closely associated with actin filaments forming the fertilization cone. Later PYK2 activation was evident throughout the entire oocyte cortex, however activation was most intense over the animal hemisphere. Fertilization-induced PYK2 activation could be blocked by suppressing calcium transients in the ooplasm via injection of BAPTA as a calcium chelator. PYK2 activation could be artificially induced in unfertilized oocytes by injection of IP3 at concentrations sufficient to induce calcium release. Functionally, suppression of PYK2 activity by chemical inhibition or by injection of a dominant-negative construct encoding the N-terminal ERM domain of PKY2 inhibited formation of an organized fertilization cone and reduced the frequency of successful sperm incorporation. Together, the above findings support a model in which PYK2 responds to the fertilization-induced calcium transient by promoting reorganization of the cortical actin cytoskeleton to form the fertilization cone.

Pycnogenol attenuates the inflammatory and nitrosative stress on joint inflammation induced by urate crystals

Acute gouty arthritis results from monosodium urate (MSU) crystal deposition in joint tissues. Deposited MSU crystals induce an acute inflammatory response which leads to damage of joint tissue. Pycnogenol (PYC), an extract from the bark of Pinus maritime, has documented antiinflammatory and antioxidant properties. The present study aimed to investigate whether PYC had protective effects on MSU-induced inflammatory and nitrosative stress in joint tissues both in vitro and in vivo. MSU crystals upregulated cyclooxygenase 2 (COX-2), interleukin 8 (IL-8) and inducible nitric oxide synthase (iNOS) gene expression in human articular chondrocytes, but only COX-2 and IL-8 in synovial fibroblasts. PYC inhibited the up-regulation of COX-2, and IL-8 in both articular chondrocytes and synovial fibroblasts. PYC attenuated MSU crystal induced iNOS gene expression and NO production in chondrocytes. Activation of NF-κB and SAPK/JNK, ERK1/2 and p38 MAP kinases by MSU crystals in articular chondrocytes and synovial fibroblasts in vitro was attenuated by treatment with PYC. The acute inflammatory cell infiltration and increased expression of COX-2 and iNOS in synovial tissue and articular cartilage following intra-articular injection of MSU crystals in a rat model was inhibited by coadministration of PYC. Collectively, this study demonstrates that PYC may be of value in treatment of MSU crystal-induced arthritis through its anti-inflammatory and anti-nitrosative activities.

Monosodium Urate and Tumor Necrosis Factor-α Increase Apoptosis in Human Chondrocyte Cultures

Monosodium urate and tumor necrosis factor-α, are two potent mediators of separate inflammatory response pathways in arthritic joints where inflammation may be accompanied by the loss of chondrocyte vitality via apoptosis. To address this possibility in vitro, chondrocyte cultures were employed to determine the extent to which monosodium urate and recombinant TNF-α altered the frequency of apoptotic chondrocytes. Apoptosis as a function of the activation of p38 kinase, C-Jun-terminal kinase, signal transducer and activator of transcription-3 and/or the activity of xanthine oxidase was also studied. Using normal human chondrocytes, monosodium urate or recombinant tumor necrosis factor-α increased the frequency of apoptosis and activity of xanthine oxidase. However, the xanthine oxidase-specific inhibitor, febuxostat, failed to blunt this response. Monosodium urate, tumor necrosis factor-α or the Janus kinase inhibitor, AG-490, increased the frequency of apoptotic nuclei in macroaggregate pellet cultures initiated from juvenile human chondrocytes, but not in pellet cultures derived from mesenchymal stem cells. In OA chondrocytes, activation of p38, C-Jun-NH₂-kinase and signal transducer and activator of transcription-3 preceded apoptosis. Activation of signal transducer and activator of transcription-3 also was seen in pellet cultures initiated from juvenile chondrocytes and MSCs incubated with MSU, recombinant tumor necrosis factor-α or febuxostat, but apoptosis was increased only in the pellet cultures derived from juvenile chondrocytes. Although AG-490 or the combination of AG-490 and febuxostat inhibited signal transducer and activator of transcription-3 activation, apoptosis was unaffected. These results showed that recombinant tumor necrosis factor-α, monosodium urate and AG-490 increased apoptosis in normal human chondrocytes, OA chondrocytes and human juvenile chondrocyte pellet cultures, but not in chondrocyte pellet cultures initiated from MSCs. The increased frequency of apoptotic chondrocytes in response to recombinant tumor necrosis factor-α or monosodium urate was not dependent on either activation of STAT3 or the activity of XO.

Profiling insulin like factor 3 (INSL3) signaling in human osteoblasts

BACKGROUND

Young men with mutations in the gene for the INSL3 receptor (Relaxin family peptide 2, RXFP2) are at risk of reduced bone mass and osteoporosis. Consistent with the human phenotype, bone analyses of Rxfp2(-/-) mice showed decreased bone volume, alterations of the trabecular bone, reduced mineralizing surface, bone formation, and osteoclast surface. The aim of this study was to elucidate the INSL3/RXFP2 signaling pathways and targets in human osteoblasts.

METHODOLOGY/PRINCIPAL FINDINGS

Alkaline phosphatase (ALP) production, protein phosphorylation, intracellular calcium, gene expression, and mineralization studies have been performed. INSL3 induced a significant increase in ALP production, and Western blot and ELISA analyses of multiple intracellular signaling pathway molecules and their phosphorylation status revealed that the MAPK was the major pathway influenced by INSL3, whereas it does not modify intracellular calcium concentration. Quantitative Real Time PCR and Western blotting showed that INSL3 regulates the expression of different osteoblast markers. Alizarin red-S staining confirmed that INSL3-stimulated osteoblasts are fully differentiated and able to mineralize the extracellular matrix.

CONCLUSIONS/SIGNIFICANCE

Together with previous findings, this study demonstrates that the INSL3/RXFP2 system is involved in bone metabolism by acting on the MAPK cascade and stimulating transcription of important genes of osteoblast maturation/differentiation and osteoclastogenesis.

Inhibition of Inducible Nitric Oxide Synthase Attenuates Monosodium Urate-induced Inflammation in Mice

The present study elucidated the effect of the selective inducible nitric oxide synthase (iNOS) inhibitor N⁶-(1-iminoethyl)-L-lysine (L-NIL) on monosodium urate (MSU) crystal-induced inflammation and edema in mice feet. L-NIL (5 or 10 mg/kg/day) was administered intraperitoneally 4 h before injection of MSU (4 mg) into the soles of mice hindlimb feet. Twenty-four hours after MSU injection, foot thickness was increased by 160% and L-NIL pretreatment reduced food pad swelling in a dose dependent manner. Pretreatment of 10 mg/kg/day L-NIL significantly suppressed the foot pad swelling by MSU. Plasma level of nitric oxide (NO) metabolites and gene expression and protein level of iNOS in feet were increased by MSU, which was suppressed by L-NIL pretreatment. Similar pattern of change was observed in nitrotyrosine level. MSU increased the gene expression of tumor necrosis factor (TNF)-α and interleukin (IL)-1β and L-NIL pretreatment suppressed MSU-induced cytokines expression. The mRNA levels of superoxide dismutase and glutathione peroxidase1 were increased by MSU and L-NIL pretreatment normalized the gene expression. Phosphorylation of extracellular signal-regulated kinase 1/2 and p38 was increased by MSU, which was suppressed by L-NIL pretreatment. The mRNA levels of iNOS, TNF-α, and IL-1β were increased by MSU in human dermal fibroblasts, C2C12 myoblasts, and human fetal osteoblasts in vitro, which was attenuated by L-NIL in a dose dependent manner. This study shows that L-NIL inhibits MSU-induced inflammation and edema in mice feet suggesting that iNOS might be involved in MSU-induced inflammation.

Chondrocyte AMP-activated protein kinase activity suppresses matrix degradation responses to proinflammatory cytokines interleukin-1β and tumor necrosis factor α

OBJECTIVE

Interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα) stimulate chondrocyte matrix catabolic responses, thereby compromising cartilage homeostasis in osteoarthritis (OA). AMP-activated protein kinase (AMPK), which regulates energy homeostasis and cellular metabolism, also exerts antiinflammatory effects in multiple tissues. This study was undertaken to test the hypothesis that AMPK activity limits chondrocyte matrix catabolic responses to IL-1β and TNFα.

METHODS

Expression of AMPK subunits was examined, and AMPKα activity was ascertained by the phosphorylation status of AMPKα Thr(172) in human knee articular chondrocytes and cartilage by Western blotting and immunohistochemistry, respectively. Procatabolic responses to IL-1β and TNFα, such as release of glycosaminoglycan, nitric oxide, and matrix metalloproteinases 3 and 13 were determined by dimethylmethylene blue assay, Griess reaction, and Western blotting, respectively, in cartilage explants and chondrocytes with and without knockdown of AMPKα by small interfering RNA.

RESULTS

Normal human knee articular chondrocytes expressed AMPKα1, α2, β1, β2, and γ1 subunits. AMPK activity was constitutively present in normal articular chondrocytes and cartilage, but decreased in OA articular chondrocytes and cartilage and in normal chondrocytes treated with IL-1β and TNFα. Knockdown of AMPKα resulted in enhanced catabolic responses to IL-1β and TNFα in chondrocytes. Moreover, AMPK activators suppressed cartilage/chondrocyte procatabolic responses to IL-1β and TNFα and the capacity of TNFα and CXCL8 (IL-8) to induce type X collagen expression.

CONCLUSION

Our findings indicate that AMPK activity is reduced in OA cartilage and in chondrocytes following treatment with IL-1β or TNFα. AMPK activators attenuate dephosphorylation of AMPKα and procatabolic responses in chondrocytes induced by these cytokines. These observations suggest that maintenance of AMPK activity supports cartilage homeostasis by protecting cartilage matrix from inflammation-induced degradation.

Tophaceous gout of the knee: revisiting MRI patterns in 30 patients

OBJECTIVE

To evaluate the locations and associated erosions of tophaceous gout in the knee and to reevaluate its characteristic magnetic resonance imaging features.

MATERIALS AND METHODS

We performed a retrospective review of the magnetic resonance (MR) images of the knees of 30 patients with histopathologically confirmed gouty tophi. Each tophaceous lesion was evaluated for location, morphology, signal intensity, and associated bone erosion or intraosseous involvement.

RESULTS

The tophaceous masses were commonly located on the medial aspect of the infrapatellar fat pad and anterior joint recess (n = 28, 87%), the space adjacent to the lateral rim of the lateral femoral condyle (n = 25, 78%), and the intercondylar fossae (n = 22, 69%). All tophaceous lesions showed similar signal characteristics (low-intermediate signal intensities on T1-weighted images, with heterogeneous signal intensities on T2-weighted images), and 3 morphologic patterns were observed: amorphous masses (n = 27), linear crystalline-like deposits (n = 6), and cystic lesions of the bursae around the knee (n = 3). Associated bone erosions occurred in the lateral rim of the lateral femoral condyle (n = 8), the roof of the intercondylar notch (n = 7), the tibial eminence (n = 5), and the medial and lateral rim of the tibial plateau (n = 3). Intraosseous tophi were seen in the tibial plateau (n = 3) and patella (n = 1).

CONCLUSION

Knowledge of the common locations and associated erosions of tophaceous gout and its characteristic MR appearance may facilitate its correct diagnosis with magnetic resonance imaging, particularly in patients with no clinical symptom or only an isolated lesion on MR images.

The role of uric acid and other crystals in osteoarthritis

Clinicians have long assumed that an association exists between crystal arthropathies and the presence of osteoarthritis (OA). However, studies establishing an independent association between calcium pyrophosphate or uric acid crystal disease and OA are sparse. Even less is known about a possible pathogenic relationship. Whereas some studies suggest that the relationships between crystals and OA may not be incidental and that crystal deposition may contribute to the onset and/or acceleration of OA joint damage, other authors have challenged this assertion. In this review, we provide an overview of past and current research elucidating the role of crystal deposition, including monosodium urate, calcium pyrophosphate, and other crystals, in OA. Given the clinical frequency of gout and that agents exist to modulate serum UA levels, special attention is given to the role of monosodium urate crystals.

Mitogen-activated protein kinases as therapeutic targets in osteoarthritis

PURPOSE OF REVIEW

The mitogen-activated protein (MAP) kinases are intracellular signaling proteins which play a central role in controlling the activity of pathways that regulate production and activity of multiple mediators of joint tissue destruction. The therapeutic potential of MAP kinase inhibition in osteoarthritis was reviewed.

RECENT FINDINGS

Results from basic research studies support the role of MAP kinases as central mediators that regulate expression of proinflammatory cytokines and metalloproteinases but also as potential pain mediators as well. Cell culture and animal model studies suggest that inhibition of MAP kinases might slow progression of osteoarthritis but trials of MAP kinase inhibitors in humans with osteoarthritis have not yet been reported. Safety concerns of the currently available inhibitors have limited their initial use to trials in conditions considered more severe than osteoarthritis.

SUMMARY

MAP kinase inhibition has the potential to slow disease progression in osteoarthritis and also might reduce pain; however, safety concerns have limited the use of general MAP kinase inhibitors in humans. Further understanding of the function of specific isoforms of the MAP kinases as well as upstream and downstream effectors may lead to the development of more specific inhibitors with less toxicity that could eventually be used as structure-modifying drugs for osteoarthritis.

Chondroprotective effects of glucosamine involving the p38 MAPK and Akt signaling pathways

The purpose of the present study was to elucidate the possible signal transduction pathway involved in the underlying mechanism of glucosamine (GLN)'s influence on the gene expression of matrix metalloproteinases (MMPs) in chondrocytes stimulated with IL-1beta. Using chondrosarcoma cells stimulated with IL-1beta, the effects of GLN on the mRNA and protein levels of MMP-3, the activation of JNK, ERK, p38, NF-kappaB, and AP-1, the nuclear translocation of NF-kappaB/Rel family members, and PI3-kinase/Akt activation were studied. GLN inhibited the expression and the synthesis of MMP-3 induced by IL-1beta, and that inhibition was mediated at the level of transcription involving both the NF-kappaB and AP-1 transcription factors. Translocation of NF-kappaB was reduced by GLN as a result of the inhibition of IkappaB degradation. A slightly synergistic effect on the activation of AP-1 induced by IL-1beta was shown in the presence of GLN. Among MAPK pathways involved in the transcriptional regulation of AP-1, phosphorylation of JNK and ERK was found to increase with the presence of GLN under IL-1beta treatment, while that for p38 decreased. It was also found that GLN alone, but also synergistically with IL-1beta, was able to activate the Akt pathway. The requirements of NF-kappaB translocation and p38 activity are indispensably involved in the induction of MMP-3 expression in chondrosarcoma cells stimulated by IL-1beta. Inhibition of the p38 pathway in the presence of GLN substantially explains the chondroprotective effect of GLN on chondrocytes that regulate COX-2 expression, PGE(2) synthesis, and NO expression and synthesis. The chondroprotective effect of GLN through the decrease in MMP-3 production and stimulation of proteoglycan synthesis may follow another potential signaling pathway of Akt.

Human articular chondrocytes produce IL-7 and respond to IL-7 with increased production of matrix metalloproteinase-13

Introduction

Fibronectin fragments have been found in the articular cartilage and synovial fluid of patients with osteoarthritis and rheumatoid arthritis. These matrix fragments can stimulate production of multiple mediators of matrix destruction, including various cytokines and metalloproteinases. The purpose of this study was to discover novel mediators of cartilage destruction using fibronectin fragments as a stimulus.

Methods

Human articular cartilage was obtained from tissue donors and from osteoarthritic cartilage removed at the time of knee replacement surgery. Enzymatically isolated chondrocytes in serum-free cultures were stimulated overnight with the 110 kDa α5β1 integrin-binding fibronectin fragment or with IL-1, IL-6, or IL-7. Cytokines and matrix metalloproteinases released into the media were detected using antibody arrays and quantified by ELISA. IL-7 receptor expression was evaluated by flow cytometry, immunocytochemical staining, and PCR.

Results

IL-7 was found to be produced by chondrocytes treated with fibronectin fragments. Compared with cells isolated from normal young adult human articular cartilage, increased IL-7 production was noted in cells isolated from older adult tissue donors and from osteoarthritic cartilage. Chondrocyte IL-7 production was also stimulated by combined treatment with the catabolic cytokines IL-1 and IL-6. Chondrocytes were found to express IL-7 receptors and to respond to IL-7 stimulation with increased production of matrix metalloproteinase-13 and with proteoglycan release from cartilage explants.

Conclusion

These novel findings indicate that IL-7 may contribute to cartilage destruction in joint diseases, including osteoarthritis.

Subcutaneous tendon rupture of extensor tendons on bilateral wrists associated with calcium pyrophosphate dihydrate crystal deposition disease

Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease is a well-recognized inflammatory joint disorder. Extensor tendon rupture associated with CPPD deposition has rarely been described. We report herein the case of a 58-year-old woman who underwent reconstruction for subcutaneous extensor tendon ruptures of the extensor tendons for the ring and little fingers on both wrists associated with CPPD deposition. The significance of this case is the occurrence at an earlier age compared to previous papers and the appearance on bilateral wrists.

Uric acid inhibits renal proximal tubule cell proliferation via at least two signaling pathways involving PKC, MAPK, cPLA2, and NF-kappaB

The accumulation of uric acid, an end-product of purine metabolism, is responsible for the many deleterious effects observed in gouty arthritis, including renal injury. Here, we present evidence that under conditions of hyperuricemia (>10(-4) M uric acid) [(3)H]thymidine incorporation into primary renal proximal tubule cells (PTCs) is inhibited, and we delineate the signaling pathways involved. Elevated uric acid was observed to stimulate MAPK phosphorylation. The uric acid induced p38 MAPK phosphorylation was also blocked by H-7 (a PKC inhibitor), indicating that p38 MAPK was a downstream target of PKC. Evidence that cytoplasmic phospholipase A(2) (cPLA(2)) was involved further downstream included 1) the stimulatory effect of uric acid on [(3)H]-labeled arachidonic acid (AA) release; 2) the stimulation of AA release in response to uric acid was blocked by the PKC inhibitor H-7 as well as by the p38 MAPK inhibitor SB 203580; and 3) the uric acid-induced inhibition of [(3)H]thymidine incorporation was prevented by SB 203580, as well as by the cPLA(2) inhibitor arachidonyl trifluoromethyl ketone, and mepacrine (another PLA(2) inhibitor). Evidence of a uric acid-induced activation of NF-kappaB as well as PLA(2) was obtained. Moreover the uric acid-induced inhibition of [(3)H]thymidine incorporation was also blocked by two NF-kappaB inhibitors, pyrrolidine dithiocarbamate and SN 50. However, SN 50 did not block the uric acid induced [(3)H]AA release. Thus the inhibition of [(3)H]thymidine incorporation caused by uric acid can be explained by two distinct mechanisms, the activation of NF-kappaB as well as the activation of PLA(2).

Gout: Update on Some Pathogenic and Clinical Aspects

Pathogenesis of gout inflammation remains unknown, but recent advances have been made with respect to initiation, amplification, and self-limitation. Direct crystal-cell membrane contact leads to cell activation, involving membrane-associated molecules. Resolution of acute gout inflammation is a mechanism that is controlled by monocyte-macrophage switch, which results in the loss of cytokine production capability and, conversely, the ability to produce anti-inflammatory molecules. MRI and ultrasound findings provide preliminary data that are not yet used in clinical trials. Diagnosis and management recommendations are missing, but this gap will be filled soon with the upcoming European League Against Rheumatism Task Force's recommendations on gout.