Limited effect of anti-rheumatic treatment on 15-prostaglandin dehydrogenase in rheumatoid arthritis synovial tissue

Lipidomic Profiling in Synovial Tissue

The analysis of synovial tissue offers the potential for the comprehensive characterization of cell types involved in arthritis pathogenesis. The studies performed to date in synovial tissue have made it possible to define synovial pathotypes, which relate to disease severity and response to treatment. Lipidomics is the branch of metabolomics that allows the quantification and identification of lipids in different biological samples. Studies in animal models of arthritis and in serum/plasma from patients with arthritis suggest the involvement of different types of lipids (glycerophospholipids, glycerolipids, sphingolipids, oxylipins, fatty acids) in the pathogenesis of arthritis. We reviewed studies that quantified lipids in different types of tissues and their relationship with inflammation. We propose that combining lipidomics with currently used “omics” techniques can improve the information obtained from the analysis of synovial tissue, for a better understanding of pathogenesis and the development of new therapeutic strategies.

Robust COX-2-mediated prostaglandin response may drive arthralgia and bone destruction in patients with chronic inflammation post-chikungunya

Patients following infection by chikungunya virus (CHIKV) can suffer for months to years from arthralgia and arthritis. Interestingly, methotrexate (MTX) a major immune-regulatory drug has proved to be of clinical benefit. We have previously shown that CHIKV can persist in the joint of one patient 18 months post-infection and plausibly driving chronic joint inflammation but through ill-characterized mechanisms. We have pursued our investigations and report novel histological and in vitro data arguing for a plausible role of a COX-2-mediated inflammatory response post-CHIKV. In the joint, we found a robust COX-2 staining on endothelial cells, synovial fibroblasts and more prominently on multinucleated giant cells identified as CD11c+ osteoclasts known to be involved in bone destruction. The joint tissue was also strongly stained for CD3, CD8, CD45, CD14, CD68, CD31, CD34, MMP2, and VEGF (but not for NO synthase and two B cell markers). Dendritic cells were rarely detected. Primary human synovial fibroblasts were infected with CHIKV or stimulated either by the synthetic molecule polyriboinosinic:polyribocytidylic acid (PIC) to mimic chronic viral infection or cytokines. First, we found that PIC and CHIKV enhanced mRNA expression of COX-2. We further found that PIC but not CHIKV increased the mRNA levels of cPLA2α and of mPGES-1, two other central enzymes in PGE2 production. IFNβ upregulated cPLA2α and COX-2 transcription levels but failed to modulated mPGES-1 mRNA expression. Moreover, PIC, CHIKV and IFNβ decreased mRNA expression of the PGE2 degrading enzyme 15-PGDH. Interestingly, MTX failed to control the expression of all these enzymes. In sharp contrast, dexamethasone was able to control the capacity of pro-inflammatory cytokines, IL-1β as well as TNFα, to stimulate mRNA levels of cPLA2α, COX-2 and mPGES-1. These original data argue for a concerted action of CHIKV (including viral RNA) and cytokines plausibly released from recruited leukocytes to drive a major COX-2-mediated PGE2 proinflammatory responses to induce viral arthritis.

It is important to have a better understanding of the immuno-pathogenesis of Chikungunya virus (CHIKV) and particularly focusing on the chronic phase associated to arthralgia and arthritis. Benefiting from our prospective cohort studies, we herein provide novel in vivo data identifying for the first time the implication of COX-2 and several other enzymes involved in prostaglandin biosynthesis and the persistence of the virus on the joint. Prostaglandin has major activities in inflammation and joint destruction. In vitro, we have used a model of human synovial fibroblasts to decipher the regulatory mechanisms of prostaglandin biosynthesis pathway. We have made important observations showing that the virus itself as well as major inflammatory cytokines can dramatically control the expression of all enzymes involved in the metabolism of prostaglandin. Interestingly, pharmacological investigations further revealed that dexamethasone, but not methotrexate (currently used to treat patients with chikungunya) may be of clinical values.

The regulatory mechanism involved in the prostaglandin E2 disposition in carbon tetrachloride-induced liver injury

Prostaglandin E₂ (PGE₂) exhibits hepatoprotective effects against various types of liver injury. However, there is little information on the disposition of endogenous PGE₂ during liver injury. In the present study, we attempted to elucidate the mechanism involved in regulating PGE₂ distribution during liver injury. Carbon tetrachloride (CCl₄) was used to establish a liver injury mouse model. PGE₂ was measured by LC-MS/MS. The plasma and hepatic PGE₂ levels were significantly increased at 6 to 48 h after CCl₄ treatment. The ratio of plasma levels of 13,14-dihydro-15-ketoPGE₂ (PGEM), a major PGE₂ metabolite, to PGE₂ decreased significantly after CCl₄ treatment. PGE₂ synthesis and expression of enzymes related to PGE₂ production were not induced, while the activity and mRNA expression of 15-prostaglandin dehydrogenase (15-PGDH/Hpgd), a major enzyme for PGE₂ inactivation, decreased significantly in the liver of CCl₄-treated mice compared to that of vehicle-treated control. The plasma and hepatic PGE₂ levels were negatively correlated with the hepatic mRNA expression levels of Hpgd. Although the mRNA expression of organic anion transporting polypeptide 2A1 (OATP2A1/Slco2a1), a major PGE₂ transporter, was upregulated, other hepatic OATPs decreased significantly at 24 h after CCl₄ treatment. Immunohistochemical analysis indicated that 15-PGDH was mainly expressed in endothelial cells and that OATP2A1 was expressed at least in endothelial cells and Kupffer cells in the liver. These results suggest that the decreased 15-PGDH expression in hepatic endothelial cells is the principal mechanism for the increase in hepatic and plasma PGE₂ levels due to the CCl₄-induced liver injury.

Methotrexate an Old Drug with New Tricks

Methotrexate (MTX) is the first line drug for the treatment of a number of rheumatic and non-rheumatic disorders. It is currently used as an anchor disease, modifying anti-rheumatic drug in the treatment of rheumatoid arthritis (RA). Despite the development of numerous new targeted therapies, MTX remains the backbone of RA therapy due to its potent efficacy and tolerability. There has been also a growing interest in the use of MTX in the treatment of chronic viral mediated arthritis. Many viruses—including old world alphaviruses, Parvovirus B19, hepatitis B/C virus, and human immunodeficiency virus—have been associated with arthritogenic diseases and reminiscent of RA. MTX may provide benefits although with the potential risk of attenuating patients’ immune surveillance capacities. In this review, we describe the emerging mechanisms of action of MTX as an anti-inflammatory drug and complementing its well-established immunomodulatory activity. The mechanisms involve adenosine signaling modulation, alteration of cytokine networks, generation of reactive oxygen species and HMGB1 alarmin suppression. We also provide a comprehensive understanding of the mechanisms of MTX toxic effects. Lastly, we discussed the efficacy, as well as the safety, of MTX used in the management of viral-related rheumatic syndromes.

Cytokine-induced endogenous production of prostaglandin D2 is essential for human group 2 innate lymphoid cell activation

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) play a key role in the initiation and maintenance of type 2 immune responses. The prostaglandin (PG) D₂-chemoattractant receptor-homologous molecule expressed on T_H2 cells (CRTH2) receptor axis potently induces cytokine production and ILC2 migration.

OBJECTIVE

We set out to examine PG production in human ILC2s and the implications of such endogenous production on ILC2 function.

METHODS

The effects of the COX-1/2 inhibitor flurbiprofen, the hematopoietic prostaglandin D₂ synthase (HPGDS) inhibitor KMN698, and the CRTH2 antagonist CAY10471 on human ILC2s were determined by assessing receptor and transcription factor expression, cytokine production, and gene expression with flow cytometry, ELISA, and quantitative RT-PCR, respectively. Concentrations of lipid mediators were measured by using liquid chromatography-tandem mass spectrometry and ELISA.

RESULTS

We show that ILC2s constitutively express HPGDS and upregulate COX-2 upon IL-2, IL-25, and IL-33 plus thymic stromal lymphopoietin stimulation. Consequently, PGD₂ and its metabolites can be detected in ILC2 supernatants. We reveal that endogenously produced PGD₂ is essential in cytokine-induced ILC2 activation because blocking of the COX-1/2 or HPGDS enzymes or the CRTH2 receptor abolishes ILC2 responses.

CONCLUSION

PGD₂ produced by ILC2s is, in a paracrine/autocrine manner, essential in cytokine-induced ILC2 activation. Hence we provide the detailed mechanism behind how CRTH2 antagonists represent promising therapeutic tools for allergic diseases by controlling ILC2 function.

LAIR-1 shedding from human fibroblast-like synoviocytes in rheumatoid arthritis following TNF-α stimulation

This study examined the expression of the inhibitory receptor, leucocyte-associated immunoglobulin (Ig)-like receptor-1 (LAIR-1) in fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA) patients to investigate its potential role in the modulation of inflammatory cytokines, matrix metalloproteinases (MMPs) and invasiveness of synoviocytes. LAIR-1 expression in synovial tissues from RA patients, osteoarthritis patients and healthy donors was analysed by immunohistochemistry. The membrane-bound form (mLAIR-1) was detected by flow cytometry. Factors involved in inflammation and MMP activity in FLS were analysed by quantitative polymerase chain reaction (qPCR). LAIR-1 expression was higher in the synovia of the RA patients than those of the osteoarthritis patients. Co-immunostaining of vimentin/LAIR-1 demonstrated that LAIR-1 was localized mainly in FLS in the RA patients. Surprisingly, primary FLS isolated from the RA patients had low levels of mLAIR-1 expression, with cytoplasmic distribution. The extracellular domain of LAIR-1 was shed from the cell surface in response to tumour necrosis factor (TNF)-α, and this process could be blocked by serine protease inhibitors. Additional experiments indicated that LAIR-1 over-expression reduced FLS invasion considerably, which reduced simultaneously the mRNA levels of interleukin (IL)-6, IL-8 and MMP-13 in the presence of TNF-α. Our study demonstrated that LAIR-1 is an anti-inflammatory molecule, and was up-regulated in FLS in the RA patients; however, cell-surface LAIR-1 could be shed from cells in the inflammatory microenvironment in RA. This may weaken the interaction of LAIR-1 with its ligand, thus reducing the anti-inflammatory effects of LAIR-1. These findings suggested that LAIR-1 may be an important factor involved in the mediation of the progressive joint destruction in RA.

Serum Levels of MDC and MMP-9 and the Relationship Between Serum Levels and Disease Activity in the Patients with Systemic Lupus Erythematosus

BACKGROUND AND OBJECTIVE

Systemic lupus erythematosus (SLE) is a complicated autoimmune disease. Although its pathogenesis is not clear, cytokine may be involved in it. So we investigated serum levels of macrophage-derived chemokine (MDC), and matrix metalloproteinase-9 (MMP-9), and to determine the relationship between serum levels and the disease activity of SLE.

METHODS

Serum levels of MDC and MMP-9 were measured by enzyme-linked immuno sorbent assay (ELISA).

RESULTS

Significantly decreased serum levels of MDC and MMP-9 were found in SLE as compared to those in controls (P<0.001 P<0.001), but serum levels of MDC and MMP-9 increased after treatment (P<0.001 P<0.05). Serum levels of MDC and MMP-9 were lower in patients with active disease than those with inactive disease (P<0.001 P<0.05). Significantly decreased serum levels of MDC and MMP-9 were found in patients with renal damage than those without the damage (P<0.001 P<0.05). Serum level of MDC was lower in patients with arthritis than those without the damage (P<0.001), but serum level of MMP-9 has no significant difference in two groups (P>0.05).

CONCLUSION

The present data suggest that MDC and MMP-9 may be involved in the pathogenesis of SLE, and serum levels of MDC and MMP-9 could be markers of monitoring disease activity, renal damage, disease progression and improvement in SLE.

15-hydroxyprostaglandin dehydrogenase is upregulated by hydroxychloroquine in rheumatoid arthritis fibroblast-like synoviocytes

15-Hydroxyprostaglandin dehydrogenase (HPGD) is the key enzyme responsible for the metabolic inactivation of prostaglandin E2 (PGE₂) catabolism. PGE₂ is one of the predominant catabolic factors involved in rheumatoid arthritis (RA). However, the expression and regulation of HPGD in RA fibroblast-like synoviocyte (FLS) remain to be elucidated. Disease-modifying anti-rheumatic drugs (DMARDs) are the most important anti-arthritic drugs, which reduce the effect of joint injury. The aim of the present study was to assess the expression of HPGD in RA tissues and cells, and normal synovial tissues and cells. The effect of the most popular DMARDs, hydroxychloroquine, on the expression of HPGD in RA-FLS was also investigated. Western blotting and immuno-histochemical analysis demonstrated that the expression levels of HPGD in human synovium were lower in RA synovium compared with the normal and OA synovium. In RA-FLS, the expression of HPGD was increased following treatment with several DMARDs, including sulfasalazine, methotrexate, and hydroxychloroquine. Hydroxychloroquine (10 µM) treatment induced the phosphorylation of ERK, SAPK/JNK and p38. Hydroxychloroquine induced a decrease in the release of PGE₂, which was restored by mitogen-activated protein (MAP) kinase pathway inhibitors. Hydroxychloroquine may therefore, affect the pathogenesis of RA through the MAP kinase pathway by regulating the expression of HPGD.

IL-1β/HMGB1 complexes promote The PGE2 biosynthesis pathway in synovial fibroblasts

PGE₂ is a potent lipid mediator of pain and oedema found elevated in RA. Microsomal prostaglandin E synthase-1 (mPGES-1) is a terminal enzyme of the PGE₂ pathway inducible by proinflammatory cytokines. mPGES-1 is markedly upregulated in RA synovial tissue despite antirheumatic treatments, suggesting that multiple inflammatory stimuli contribute to its induction. High-mobility group box chromosomal protein 1 (HMGB1) is known to induce inflammation both by direct interaction with TLR4 and by enhancement of other proinflammatory molecules signalling, through complex formation. The high expression of extracellular HMGB1 within the inflamed synovium, implies its pro-arthritogenic role in RA. We aimed to investigate the effects of IL-1β/HMGB1 complexes on mPGES-1 and other enzymes of the PGE₂ pathway in synovial fibroblasts (SFs) from patients with arthritis. Furthermore, we studied the effect of COX-2 inhibition and IL-1RI antagonism on prostanoid and cytokine production by SFs. Stimulation of SFs with HMGB1 in complex with suboptimal amounts of IL-1β significantly increased mPGES-1 and COX-2 expressions as well as PGE₂ production, as compared to treatment with HMGB1 or IL-1β alone. Furthermore, NS-398 reduced the production of IL-6 and IL-8, thus indicating that IL-1β/HMGB1 complexes modulate cytokine production in part through prostanoid synthesis. Treatment with IL-1RA completely abolished the induced PGE₂ and cytokine production, suggesting an effect mediated through IL-1RI. IL-1β/HMGB1 complexes promote the induction of mPGES-1, COX-2 and PGE₂ in SF. The amplification of the PGE₂ biosynthesis pathway by HMGB1 might constitute an important pathogenic mechanism perpetuating inflammatory and destructive activities in rheumatoid arthritis.

Prostaglandin D(2) in inflammatory arthritis and its relation with synovial fluid dendritic cells

Prostaglandin (PG)D2 has been shown to be an active agent in the resolution of experimentally induced inflammation. This study was undertaken to determine the presence of PGD2 in chronic joint effusions and to explore the potential contributions of dendritic cells (DC) and monocytes to the intra-articular synthesis of PGD2. Synovial fluid (SF) was obtained from patients with inflammatory arthritis and knee effusions. PGD2 and PGE2 were detected in SF by ultrahigh-performance tandem mass spectrometry. Cellular fractions in SF were separated by density-gradient centrifugation and flow cytometry. The expression of hematopoietic prostaglandin D-synthase (hPGDS) and PGE-synthase (PGES) mRNA was determined by RT-PCR. Both PGD2 and PGE2 were detected in blood and SF, with PGD2 being more abundant than PGE2 in SF. mRNA for hPGDS was more abundant in SF mDCs than SF monocytes (P < 0.01) or PB monocytes (P < 0.001). SF mDC expressed significantly more hPGDS than PGES. Expressions of PGD2 and hPGDS were inversely associated with serum C-reactive protein (P < 0.01) and erythrocyte sedimentation rate (P < 0.01). The findings suggest that synovial DCs may be an important source of hPGDS and that systemic disease activity may be influenced by actions of PGD2 in RA and other arthropathies.