Osteostatin Mitigates Gouty Arthritis through the Inhibition of Caspase-1 Activation and Upregulation of Nrf2 Expression.

Gouty arthritis results from monosodium urate (MSU) crystal deposition in joints, initiating (pro)-interleukin (IL)-1ß maturation, inflammatory mediator release, and neutrophil infiltration, leading to joint swelling and pain. Parathyroid hormone-related protein (107-111) C-terminal peptide (osteostatin) has shown anti-inflammatory properties in osteoblasts and collagen-induced arthritis in mice, but its impact in gouty arthritis models remains unexplored. We investigated the effect of osteostatin on pyroptosis, inflammation, and oxidation in macrophages, as well as its role in the formation of calcium pyrophosphate dihydrate crystals and MSU-induced gouty arthritis in mice models. Osteostatin ameliorated pyroptosis induced by lipopolysaccharide and adenosine 5'-triphosphate (LPS + ATP) in mice peritoneal macrophages by reducing the expression of caspase-1, lactate dehydrogenase release, and IL-1ß and IL-18 secretion. Additionally, IL-6 and tumor necrosis factor-α (TNF-α) were also decreased due to the reduced activation of the NF-κB pathway. Furthermore, osteostatin displayed antioxidant properties in LPS + ATP-stimulated macrophages, resulting in reduced production of mitochondrial and extracellular reactive oxygen species and enhanced Nrf2 translocation to the nuclei. In both models of gouty arthritis, osteostatin administration resulted in reduced pro-inflammatory cytokine production, decreased leukocyte migration, and reduced caspase-1 and NF-κB activation. These results highlight the potential of osteostatin as a therapeutic option for gouty arthritis.

New Insights into the Pro-Inflammatory and Osteoclastogenic Profile of Circulating Monocytes in Osteoarthritis Patients.

Osteoarthritis (OA) is a degenerative condition of the articular cartilage with chronic low-grade inflammation. Monocytes have a fundamental role in the progression of OA, given their implication in inflammatory responses and their capacity to differentiate into bone-resorbing osteoclasts (OCLs). This observational-experimental study attempted to better understand the molecular pathogenesis of OA through the examination of osteoclast progenitor (OCP) cells from both OA patients and healthy individuals (25 OA patients and healthy samples). The expression of osteoclastogenic and inflammatory genes was analyzed using RT-PCR. The OA monocytes expressed significantly higher levels of CD16, CD115, TLR2, Mincle, Dentin-1, and CCR2 mRNAs. Moreover, a flow cytometry analysis showed a significantly higher surface expression of the CD16 and CD115 receptors in OA vs. healthy monocytes, as well as a difference in the distribution of monocyte subsets. Additionally, the OA monocytes showed a greater osteoclast differentiation capacity and an enhanced response to an inflammatory stimulus. The results of this study demonstrate the existence of significant differences between the OCPs of OA patients and those of healthy subjects. These differences could contribute to a greater understanding of the molecular pathogenesis of OA and to the identification of new biomarkers and potential drug targets for OA.

Osteostatin Inhibits M-CSF+RANKL-Induced Human Osteoclast Differentiation by Modulating NFATc1.

Parathyroid hormone-related protein (PTHrP) C-terminal peptides regulate the metabolism of bone cells. PHTrP [107-111] (osteostatin) promotes bone repair in animal models of bone defects and prevents bone erosion in inflammatory arthritis. In addition to its positive effects on osteoblasts, osteostatin may inhibit bone resorption. The aim of this study was to determine the effects of osteostatin on human osteoclast differentiation and function. We used macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor κB ligand (RANKL) to induce the osteoclast differentiation of adherent human peripheral blood mononuclear cells. Tartrate-resistant acid phosphatase (TRAP) staining was performed for the detection of the osteoclasts. The function of mature osteoclasts was assessed with a pit resorption assay. Gene expression was evaluated with qRT-PCR, and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) nuclear translocation was studied by immunofluorescence. We observed that osteostatin (100, 250 and 500 nM) decreased the differentiation of osteoclasts in a concentration-dependent manner, but it did not modify the resorptive ability of mature osteoclasts. In addition, osteostatin decreased the mRNA levels of cathepsin K, osteoclast associated Ig-like receptor (OSCAR) and NFATc1. The nuclear translocation of the master transcription factor in osteoclast differentiation NFATc1 was reduced by osteostatin. Our results suggest that the anti-resorptive effects of osteostatin may be dependent on the inhibition of osteoclastogenesis. This study has shown that osteostatin controls human osteoclast differentiation in vitro through the downregulation of NFATc1.

Relevance of Nrf2 and heme oxygenase-1 in articular diseases.

Joint conditions pose an important public health problem as they are a leading cause of pain, functional limitation and physical disability. Oxidative stress is related to the pathogenesis of many chronic diseases affecting the joints such as rheumatoid arthritis and osteoarthritis. Cells have developed adaptive protection mechanisms to maintain homeostasis such as nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) which regulates the transcription of many genes involved in redox balance, detoxification, metabolism and inflammation. Activation of Nrf2 results in the synthesis of heme oxygenase-1 (HO-1) leading to the formation of a number of bioactive metabolites, mainly CO, biliverdin and bilirubin. Ample evidence supports the notion that Nrf2 and HO-1 can confer protection against oxidative stress and inflammatory and immune responses in joint tissues. As a consequence, this pathway may control the activation and metabolism of articular cells to play a regulatory role in joint destruction thus offering new opportunities for better treatments. Further studies are necessary to identify improved strategies to regulate Nrf2 and HO-1 activation in order to enable the development of drugs with therapeutic applications in joint diseases.

Osteostatin Inhibits Collagen-Induced Arthritis by Regulation of Immune Activation, Pro-Inflammatory Cytokines, and Osteoclastogenesis.

In chronic inflammatory joint diseases, such as rheumatoid arthritis, there is an important bone loss. Parathyroid hormone-related protein (PTHrP) and related peptides have shown osteoinductive properties in bone regeneration models, but there are no data on inflammatory joint destruction. We have investigated whether the PTHrP (107-111) C-terminal peptide (osteostatin) could control the development of collagen-induced arthritis in mice. Administration of osteostatin (80 or 120 µg/kg s.c.) after the onset of disease decreased the severity of arthritis as well as cartilage and bone degradation. This peptide reduced serum IgG2a levels as well as T cell activation, with the downregulation of RORγt+CD4+ T cells and upregulation of FoxP3+CD8+ T cells in lymph nodes. The levels of key cytokines, such as interleukin(IL)-1ß, IL-2, IL-6, IL-17, and tumor necrosis factor-α in mice paws were decreased by osteostatin treatment, whereas IL-10 was enhanced. Bone protection was related to reductions in receptor activator of nuclear factor-κB ligand, Dickkopf-related protein 1, and joint osteoclast area. Osteostatin improves arthritis and controls bone loss by inhibiting immune activation, pro-inflammatory cytokines, and osteoclastogenesis. Our results support the interest of osteostatin for the treatment of inflammatory joint conditions.

Emerging therapeutic agents in osteoarthritis.

Osteoarthritis (OA) is the most common joint disorder and a leading cause of disability. Current treatments for OA can improve symptoms but do not delay the progression of disease. In the last years, much effort has been devoted to developing new treatments for OA focused on pain control, inflammatory mediators or degradation of articular tissues. Although promising results have been obtained in ex vivo studies and animal models of OA, few of these agents have completed clinical trials. Available clinical data support the interest of nerve growth factor as a target in pain control as well as the disease-modifying potential of inhibitors of Wnt signaling or catabolic enzymes such as aggrecanases and cathepsin K, and anabolic strategies like fibroblast growth factor-18 or cellular therapies. Carefully controlled studies in patients selected according to OA phenotypes and with a long follow-up will help to confirm the relevance of these new approaches as emerging therapeutic treatments in OA.

Nrf2 as a therapeutic target for rheumatic diseases.

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a master regulator of cellular protective processes. Rheumatic diseases are chronic conditions characterized by inflammation, pain, tissue damage and limitations in function. Main examples are rheumatoid arthritis, systemic lupus erythematosus, osteoarthritis and osteoporosis. Their high prevalence constitutes a major health problem with an important social and economic impact. A wide range of evidence indicates that Nrf2 may control different mechanisms involved in the physiopathology of rheumatic conditions. Therefore, the appropriate expression and balance of Nrf2 is necessary for regulation of oxidative stress, inflammation, immune responses, and cartilage and bone metabolism. Numerous studies have demonstrated that Nrf2 deficiency aggravates the disease in experimental models while Nrf2 activation results in immunoregulatory and anti-inflammatory effects. These reports reinforce the increasing interest in the pharmacologic regulation of Nrf2 and its potential applications. Nevertheless, a majority of Nrf2 inducers are electrophilic molecules which may present off-target effects. In recent years, novel strategies have been sought to modulate the Nrf2 pathway which has emerged as a therapeutic target in rheumatic conditions.

Myeloid Heme Oxygenase-1 Regulates the Acute Inflammatory Response to Zymosan in the Mouse Air Pouch.

Heme oxygenase-1 (HO-1) is induced by many stimuli to modulate the activation and function of different cell types during innate immune responses. Although HO-1 has shown anti-inflammatory effects in different systems, there are few data on the contribution of myeloid HO-1 and its role in inflammatory processes is not well understood. To address this point, we have used HO-1M-KO mice with myeloid-restricted deletion of HO-1 to specifically investigate its influence on the acute inflammatory response to zymosan in vivo. In the mouse air pouch model, we have shown an exacerbated inflammation in HO-1M-KO mice with increased neutrophil infiltration accompanied by high levels of inflammatory mediators such as interleukin-1ß, tumor necrosis factor-α, and prostaglandin E2. The expression of the degradative enzyme matrix metalloproteinase-3 (MMP-3) was also enhanced. In addition, we observed higher levels of serum MMP-3 in HO-1M-KO mice compared with control mice, suggesting the presence of systemic inflammation. Altogether, these findings demonstrate that myeloid HO-1 plays an anti-inflammatory role in the acute response to zymosan in vivo and suggest the interest of this target to regulate inflammatory processes.

Targeting inflammasome by the inhibition of caspase-1 activity using capped mesoporous silica nanoparticles.

Acute inflammation is a protective response of the body to harmful stimuli, such as pathogens or damaged cells. However, dysregulated inflammation can cause secondary damage and could thus contribute to the pathophysiology of many diseases. Inflammasomes, the macromolecular complexes responsible for caspase-1 activation, have emerged as key regulators of immune and inflammatory responses. Therefore, modulation of inflammasome activity has become an important therapeutic approach. Here we describe the design of a smart nanodevice that takes advantage of the passive targeting of nanoparticles to macrophages and enhances the therapeutic effect of caspase-1 inhibitor VX-765 in vivo. The functional hybrid systems consisted of MCM-41-based nanoparticles loaded with anti-inflammatory drug VX-765 (S2-P) and capped with poly-L-lysine, which acts as a molecular gate. S2-P activity has been evaluated in cellular and in vivo models of inflammation. The results indicated the potential advantage of using nanodevices to treat inflammatory diseases.

Chondroprotective effects of the combination chondroitin sulfate-glucosamine in a model of osteoarthritis induced by anterior cruciate ligament transection in ovariectomised rats.

CONTEXT: The efficacy of the combination chondroitin sulfate-glucosamine (CS-GlcN) in the treatment of knee osteoarthritis (OA) has been suggested in recent clinical studies. In vitro reports have also suggested anti-inflammatory and anti-resorptive effects of this combination. OBJECTIVE: The aim of this study was to characterize the effects of CS-GlcN on joint degradation in vivo including the assessment of inflammation and bone metabolism in a model of OA. MATERIALS AND METHODS: We have used the OA model induced by anterior cruciate ligament transection (ACLT) in ovariectomised rats. CS-GlcN was administered daily (oral gavage) from week 0 until week 12 after ovariectomy at the dose of 140 (CS)+175 (GlcN)(HCl) mg/kg. Histochemical analyses were performed, the levels of biomarkers and inflammatory mediators were measured by luminex or ELISA and bone microstructure was determined by µCT. RESULTS: CS-GlcN protected against cartilage degradation and reduced the levels of inflammatory mediators such as interleukin-1ß and tumor necrosis factor-α in the affected knee. In addition, serum biomarkers of inflammation and cartilage and bone degradation including matrix metalloproteinase-3, C-telopeptide of type II collagen and the ratio receptor activator of nuclear factor κB ligand/osteoprotegerin were significantly decreased by CS-GlcN. This treatment also tended to improve some bone microstructural parameters without reaching statistical significance. DISCUSSION AND CONCLUSIONS: These results demonstrate the chondroprotective effects of CS-GlcN in vivo, in the experimental model of ACLT in ovariectomised rats, and suggest that this combination may be useful to control the joint catabolic effects of inflammatory stress. These findings could have clinical relevance related to the prevention of joint degradation by CS-GlcN and support the potential development of OA treatments based on this combination.

Paracrine in vivo inhibitory effects of adipose tissue-derived mesenchymal stromal cells in the early stages of the acute inflammatory response.

BACKGROUND AIMS: Excessive or unresolved inflammation leads to tissue lesions. Adipose tissue-derived mesenchymal stromal cells (AMSCs) have shown protective effects that may be dependent on the modulation of inflammation by secreted factors. METHODS: We used the zymosan-induced mouse air pouch model at two time points (4 h and 18 h) to evaluate the in vivo effects of AMSCs and their conditioned medium (CM) on key steps of the early inflammatory response. We assessed the effects of AMSCs and CM on leukocyte migration and myeloperoxidase activity. The levels of chemokines, cytokines and eicosanoids in exudates were measured by use of enzyme-linked immunoassay or radio-immunoassay. In addition, the expression of cyclooxygenase-2 and microsomal prostaglandin E synthase-1 (mPGES-1) was studied by use of Western blotting and the phosphorylation of p65 nuclear factor-κB (NF-κB) by immunofluorescence. RESULTS: All inflammatory parameters were significantly reduced by CM and AMSCs to a similar extent at 4 h after zymosan injection with lower effects at 18 h. The observed inhibition of leukocyte migration was associated with reduced levels of chemokines and leukotriene B4. Interleukin-1ß, interleukin-6, tumor necrosis factor-α and tumor necrosis factor-stimulated gene 6 levels were significantly decreased. The downregulation of mPGES-1 was associated with inhibition of prostaglandin E2 production. Our results suggest that these anti-inflammatory effects are related, in part, to the inhibition of NF-κB activation. CONCLUSIONS: AMSCs dampen the early process of inflammation in the zymosan-induced mouse air pouch model through paracrine mechanisms. These results support the potential utility of these cells as a source of novel treatment approaches for inflammatory pathologies.

Effects of BIS076 in a model of osteoarthritis induced by anterior cruciate ligament transection in ovariectomised rats.

BACKGROUND: Osteoarthritis (OA) is the most frequent articular disease and a leading cause of disability. There is a need for effective treatments able to slow the progression of disease. Some of the available treatments are dietary supplements providing natural components. Recent studies have shown that estrogen deficiency contributes to the pathophysiological events of OA progression. METHODS: We have used the anterior cruciate ligament transection model of OA in ovariectomised rats to study the effects of BIS076, a new formulation of a natural porcine cartilage extract associated with hydroxyapatite (as a source of calcium) and vitamin D3. Cartilage degradation, proteoglycan depletion and synovitis were followed by histochemistry. Effects on bone microstructure were determined by µCT. The levels of biomarkers in serum and inflammatory mediators in knee homogenates were measured by luminex or ELISA. RESULTS: Oral administration of BIS076 reduced articular cartilage damage and serum levels of cartilage degradation markers C-telopeptide of type II collagen and cartilage oligomeric matrix protein, as well as matrix metalloproteinase-3. The local inflammatory response was down-regulated by BIS076 with lower production of pro-inflammatory cytokines and prostaglandin E2 in joint tissues. In addition, BIS076 was effective on metaphyseal bone alterations as this formulation increased volumetric bone mineral density and improved bone micro-architecture. These effects were related to the modification of bone metabolism reflected by changes in bone biomarkers with reductions in the ratio receptor activator of nuclear factor κB ligand/osteoprotegerin and the levels of tartrate-resistant acid phosphatase-5b, suggesting an inhibitory activity of BIS076 on trabecular bone resorption. CONCLUSIONS: We have demonstrated the protective properties of a new formulation (BIS076) on joint lesion and bone alterations in an experimental model of OA in ovariectomised rats. This study supports the interest of BIS076 in OA treatments.

Anti-inflammatory and joint protective effects of extra-virgin olive-oil polyphenol extract in experimental arthritis.

The consumption of extra virgin olive oil (EVOO) in Mediterranean countries has shown beneficial effects. A wide range of evidence indicates that phenolic compounds present in EVOO are endowed with anti-inflammatory properties. In this work, we evaluated the effects of EVOO-polyphenol extract (PE) in a model of rheumatoid arthritis, the collagen-induced arthritis model in mice. On day 0, DBA-1/J mice were immunized with bovine type II collagen. On day 21, mice received a booster injection. PE (100 and 200 mg/kg) was orally administered once a day from days 29 to 41 to arthritic mice. We have demonstrated that PE decreases joint edema, cell migration, cartilage degradation and bone erosion. PE significantly reduced the levels of proinflammatory cytokines and prostaglandin E2 in the joint as well as the expression of cyclooxygenase-2 and microsomal prostaglandin E synthase-1. Our data indicate that PE inhibits c-Jun N-terminal kinase, p38 and signal transducer and activator of transcription-3. In addition, PE decreases nuclear factor κB translocation leading to the down-regulation of the arthritic process. These results support the interest of natural diet components in the development of therapeutic products for arthritic conditions.

Effects of Nrf2 deficiency on bone microarchitecture in an experimental model of osteoporosis.

OBJECTIVE: Redox imbalance contributes to bone fragility. We have evaluated the in vivo role of nuclear factor erythroid derived 2-related factor-2 (Nrf2), an important regulator of cellular responses to oxidative stress, in bone metabolism using a model of postmenopausal osteoporosis. METHODS: Ovariectomy was performed in both wild-type and mice deficient in Nrf2 (Nrf2(-/-)). Bone microarchitecture was analyzed by µCT. Serum markers of bone metabolism were also measured. Reactive oxygen species production was determined using dihydrorhodamine 123. RESULTS: Sham-operated or ovariectomized Nrf2(-/-) mice exhibit a loss in trabecular bone mineral density in femur, accompanied by a reduction in cortical area in vertebrae. Nrf2 deficiency tended to increase osteoblastic markers and significantly enhanced osteoclastic markers in sham-operated animals indicating an increased bone turnover with a main effect on bone resorption. We have also shown an increased production of oxidative stress in bone marrow-derived cells from sham-operated or ovariectomized Nrf2(-/-) mice and a higher responsiveness of bone marrow-derived cells to osteoclastogenic stimuli in vitro. CONCLUSION: We have demonstrated in vivo a key role of Nrf2 in the maintenance of bone microarchitecture.

Influence of age on osteoarthritis progression after anterior cruciate ligament transection in rats.

The anterior cruciate ligament transection (ACLT) model of osteoarthritis (OA) in young rats is widely used to study the pathogenesis of OA and possible treatment approaches. As aging is a key factor in the progression of this condition, it is hypothesized that animals may vary in their responses to ACLT according to their age. The histopathological features of young (2month-old) and middle-aged (12month-old) rats in the presence or absence of ACLT were compared. The results indicated that moderate degradative changes can be detected in the knee joints of sham-operated middle-aged rats compared with young animals. After ACLT, cartilage degradation was significantly higher in middle-aged rats in relation to young animals. An increase in interleukin(IL)-1ß and IL-17 suggests the presence of a local inflammatory response represented by synovitis in ACLT rats which is not dependent on age. Our study indicates that age is an important factor affecting the pathogenesis of OA changes after ACLT and it should be considered in studies using this experimental model.

Downregulation of the inflammatory response by CORM-3 results in protective effects in a model of postmenopausal arthritis.

CO-releasing molecules (CORMs) are a new class of drugs able to release small amounts of CO in biological systems. We have shown previously that one of these molecules, CORM-3, exerts anti-inflammatory effects in animal models. The aim of this study was to assess the effects of CORM-3 on bone metabolism in a model of postmenopausal rheumatoid arthritis osteoporosis. Ovariectomy was followed by collagen-induced arthritis in female DBA-1/J mice. Animals showing arthritis on day 22 after immunization were then randomized into control and treatment groups. CORM-3 was administered at 10 mg/kg, intraperitoneally, once a day. Alendronate was administered at 100 µg/kg, orally, once a day. On days 36 and 50 after immunization, animals were killed and tissues analyzed. The arthritic score was significantly reduced by CORM-3 but not by alendronate treatment. Histopathological analyses indicated that both compounds reduced cellular infiltration and cartilage degradation. Local bone erosion and reduction in TNFα levels were seen for CORM-3 on day 50 and for alendronate on day 36. Serum levels of COMP, IL-6, MMP-3, CTX-I, alkaline phosphatase, and osteocalcin were decreased by both treatments, whereas TNFα levels were reduced by CORM-3 and TRAP-5b by alendronate. Micro-computed tomographic analysis showed protective effects on trabecular bone, which were more prominent for CORM-3 on day 36 and for alendronate on day 50. Our results suggest that CORMs represent a novel anti-inflammatory strategy to counteract joint bone erosion with partial protective effects on systemic bone loss in postmenopausal rheumatoid arthritis.

Analysis of early biochemical markers and regulation by tin protoporphyrin IX in a model of spontaneous osteoarthritis.

Age-related changes in joint tissues lead to osteoarthritis (OA). Detection of early changes in OA patients may help to initiate treatments before the establishment of irreversible joint destruction. STR/ort mice develop with age a severe degenerative joint disease that resembles human OA thus allowing the investigation of biochemical markers as well as new treatments in an accelerated time frame. We have analyzed the changes in serum levels of different mediators during the early phases of idiopathic OA in STR/ort mice. Serum levels of matrix metalloproteinase-3 (MMP-3) but not those of tumor necrosis factor-α, interleukin(IL)-1ß, IL-17 or prostaglandin E(2) correlated with histopathological changes in knees of STR/ort mice at 9 weeks. Treatment of animals with tin protoporphyrin IX (SnPP, 12 mg/kg/dayi.p.) for 4 weeks significantly reduced the progression of OA. Our data suggest that MMP-3 is a sensitive biomarker to detect early OA alterations and that SnPP could be a protective agent in OA.

Heme oxygenase-1 regulates the progression of K/BxN serum transfer arthritis.

BACKGROUND: Heme oxygenase-1 (HO-1) is induced in many cell types as a defense mechanism against stress. We have investigated the possible role of endogenous HO-1 in the effector phase of arthritis using the K/BxN serum transfer model of arthritis in HO-1 heterozygous and homozygous knock-out mice. METHODOLOGY/PRINCIPAL FINDINGS: Arthritis was induced in C57/Black-6 xFVB (HO-1(+/+), HO-1(+/-) and HO-1(-/-)) mice by intraperitoneal injection of 150 µl serum from arthritic K/BxN mice at days 0 and 2. Blood was collected and animals were sacrificed at day 10. Histological analysis was performed in ankle sections. The levels of inflammatory mediators were measured in serum and paw homogenates by enzyme-linked immunosorbent assay or Multiplex technology. The incidence of arthritis was higher in HO-1(+/-) and HO-1(-/-) groups compared with HO-1(+/+). The inflammatory response was aggravated in HO-1(+/-) mice as shown by arthritic score and the migration of inflammatory cells that could be related to the enhancement of CXCL-1 production. In addition, the HO-1(+/-) group showed proteoglycan depletion significantly higher than HO-1(+/+) mice. Serum levels of matrix metalloproteinase-3, monocyte chemotactic protein-1, plasminogen activator inhibitor-1, E-selectin and intercellular adhesion molecule-1 were increased in arthritic HO-1(-/-) mice, whereas vascular endothelial growth factor and some cytokines such as interferon-γ showed a reduction compared to HO-1(+/+) or HO-1(+/-) mice. In addition, down-regulated gene expression of ferritin, glutathione S-reductase A1 and superoxide dismutase-2 was observed in the livers of arthritic HO-1(+/-) animals. CONCLUSION/SIGNIFICANCE: Endogenous HO-1 regulates the production of systemic and local inflammatory mediators and plays a protective role in K/BxN serum transfer arthritis.

Prostaglandin D2 regulates joint inflammation and destruction in murine collagen-induced arthritis.

OBJECTIVE: Prostaglandin D2 (PGD2) may exert proinflammatory or antiinflammatory effects in different biologic systems. Although this prostanoid and the enzymes responsible for its synthesis are up-regulated by interleukin-1ß (IL-1ß) in human chondrocytes in vitro, the role of PGD2 in arthritis remains unclear. This study was undertaken to investigate the role of PGD2 in the inflammatory response and in joint destruction during the development of collagen-induced arthritis (CIA) in mice. METHODS: PGD2 and cytokine levels in mice with CIA were determined by enzyme-linked immunosorbent assay. Expression of hematopoietic PGD synthase (h-PGDS), lipocalin-type PGD synthase (l-PGDS), and DP1 and DP2 receptors was analyzed by immunohistochemical methods. PGE2 levels were determined by radioimmunoassay. RESULTS: The arthritic process up-regulated the expression of h-PGDS, l-PGDS, DP1, and DP2 in articular tissue. PGD2 was produced in the joint during the early phase of arthritis, and serum PGD2 levels increased progressively throughout the arthritic process, reaching a maximum during the late stages of CIA. Treatment of arthritic mice with the DP1 antagonist MK0524 soon after the onset of disease increased the incidence and severity of CIA as well as the local levels of IL-1ß, CXCL-1, and PGE2, whereas IL-10 levels were reduced. The administration of the DP2 antagonist CAY10595 did not modify the severity of arthritis. The injection of PGD2 into the paw, as well as the administration of the DP1 agonist BW245C, significantly lowered the incidence of CIA, the inflammatory response, and joint damage. CONCLUSION: Our findings indicate that PGD2 is produced in articular tissue during the development of CIA and plays an antiinflammatory role, acting through the DP1 receptor.

Deficiency of Nrf2 accelerates the effector phase of arthritis and aggravates joint disease.

AIMS: Although oxidative stress participates in the etiopathogenesis of rheumatoid arthritis, its importance in this inflammatory disease has not been fully elucidated. In this study, we analyzed the relevance of the transcription factor Nrf2, master regulator of redox homeostasis, in the effector phase of an animal model of rheumatoid arthritis, using the transfer of serum from K/BxN transgenic mice to Nrf2(-/-) mice. RESULTS: Nrf2 deficiency accelerated the incidence of arthritis, and animals showed a widespread disease affecting both front and hind paws. Therefore, the inflammatory response was enhanced, with increased migration of leukocytes and joint destruction in front paws. We observed an increased production of tumor necrosis factor-α, interleukin-6, and CXCL-1 in the joint, with small changes in eicosanoid levels. Serum levels of CXCL-1 and receptor activator for nuclear factor κB ligand were enhanced and osteocalcin decreased in arthritic Nrf2(-/-) mice. The expression of cyclooxygenase-2, inducible nitric oxide synthase, and peroxynitrite in the joints was higher in Nrf2 deficiency, whereas heme oxygenase-1 was downregulated. INNOVATION: Nrf2 may be a therapeutic target for arthritis. CONCLUSION: Our results support a protective role of Nrf2 against joint inflammation and degeneration in arthritis.