High-Sucrose Diet Accelerates Arthritis Progression in a Collagen-Induced Rheumatoid Arthritis Model

SCOPE

High dietary sugar and sweeteners are suspected to cause the development of rheumatoid arthritis (RA) symptoms through the induction of proinflammatory cytokine release. However, the mechanisms by which increased dietary sugar affects RA etiology are not yet fully understood. The study uses a mouse model of collagen-induced RA (CIA) to investigate the relationship between excessive sugar consumption and RA risk.

METHODS AND RESULTS

RA-associated pathological features are assessed in the nonimmunized (NI) control group, the CIA-positive control group, and the CIA + high-sucrose diet (CIA+HS, 63% calories from sucrose) group. Compared with the CIA group, the CIA+HS group shows a greater increase in paw thickness and clinical scores, as well as, a higher degree of pannus formation and inflammation in the knee, ankle, and sole tissues. Moreover, the infiltration of immune cells is increased in the CIA+HS group. Although the expression of hepatic lipogenic genes, is not altered, that of toll-like receptor (TLR4) and IL-1β is considerably elevated in the CIA+HS group.

CONCLUSIONS

These findings suggest that excessive sucrose consumption causes hepatic fibrosis and inflammation, contributing to the pathophysiology of RA.

The effect of TNF-α inhibitor treatment on microRNAs and endothelial function in collagen induced arthritis

Chronic inflammation causes dysregulated expression of microRNAs. Aberrant microRNA expression is associated with endothelial dysfunction. In this study we determined whether TNF-α inhibition impacted the expression of miRNA-146a-5p and miRNA-155-5p, and whether changes in the expression of these miRNAs were related to inflammation-induced changes in endothelial function in collagen-induced arthritis (CIA). Sixty-four Sprague-Dawley rats were divided into control (n = 24), CIA (n = 24) and CIA+etanercept (n = 16) groups. CIA and CIA+etanercept groups were immunized with bovine type-II collagen, emulsified in incomplete Freund’s adjuvant. Upon signs of arthritis, the CIA+etanercept group received 10mg/kg of etanercept intraperitoneally, every three days. After six weeks of treatment, mesenteric artery vascular reactivity was assessed using wire-myography. Serum concentrations of TNF-α, C-reactive protein, interleukin-6, vascular adhesion molecule-1 (VCAM-1) and pentraxin-3 (PTX-3) were measured by ELISA. Relative expression of circulating miRNA-146a-5p and miRNA-155-5p were determined using RT-qPCR. Compared to controls, circulating miRNA-155-5p, VCAM-1 and PTX-3 concentrations were increased, and vessel relaxation was impaired in the CIA (all p<0.05), but not in the CIA+etanercept (all p<0.05) groups. The CIA group had greater miRNA-146a-5p expression compared to the CIA+etanercept group (p = 0.005). Independent of blood pressure, miRNA-146a-5p expression was associated with increased PTX-3 concentrations (p = 0.03), while miRNA-155-5p expression was associated with impaired vessel relaxation (p = 0.01). In conclusion, blocking circulating TNF-α impacted systemic inflammation-induced increased expression of miRNA-146a-5p and miRNA-155-5p, which were associated with endothelial inflammation and impaired endothelial dependent vasorelaxation, respectively.

IL-38 and IL-36 Target Autophagy for Regulating Synoviocyte Proliferation, Migration, and Invasion in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease leading to severe joint damage and disability. Fibroblast-like synoviocytes (FLSs) mostly contribute to the joint inflammation and destruction in RA through distinct mechanisms. However, little is known about newly discovered interleukin- (IL-) 36 and IL-38 involving in the pathology of RA. Here, we assessed the effect of IL-36 and IL-38 on RA-FLS function using IL-36 and IL-38 overexpression plasmids. We found that IL-36 inhibited synoviocytes proliferation while IL-38 showed an opposite influence. Furthermore, IL-36 and IL-38 significantly sequestered or accelerated RA-FLS migration and invasion capacity, respectively. Mechanically, IL-36 and IL-38 targeted autophagy for RA-FLS modulation. Using autophagy inhibitor 3-MA and inducer compound rapamycin, we found that autophagy negatively regulated the survival, migration, and invasion of synovial cells. Based on these results, IL-38 in combination with autophagy inhibitor 3-MA treatment demonstrated the strongest blockage of the above three activities of RA-FLS, and IL-38 overexpression reversed rapamycin-inhibited cell proliferation, migration, and invasion. Moreover, injection of IL-36 can improve the symptoms of RA in a rat model of RA. Taken together, we conclude that IL-38 and IL-36 target autophagy for regulating synoviocyte proliferation, migration, and invasion in RA.

Epigenetic drug development for autoimmune and inflammatory diseases

ES-62 is the major secreted protein of the parasitic filarial nematode, Acanthocheilonema viteae. The molecule exists as a large tetramer (MW, ~240kD), which possesses immunomodulatory properties by virtue of multiple phosphorylcholine (PC) moieties attached to N-type glycans. By suppressing inflammatory immune responses, ES-62 can prevent disease development in certain mouse models of allergic and autoimmune conditions, including joint pathology in collagen-induced arthritis (CIA), a model of rheumatoid arthritis (RA). Such protection is associated with functional suppression of "pathogenic" hyper-responsive synovial fibroblasts (SFs), which exhibit an aggressive inflammatory and bone-damaging phenotype induced by their epigenetic rewiring in response to the inflammatory microenvironment of the arthritic joint. Critically, exposure to ES-62 in vivo induces a stably-imprinted CIA-SF phenotype that exhibits functional responses more typical of healthy, Naïve-SFs. Consistent with this, ES-62 "rewiring" of SFs away from the hyper-responsive phenotype is associated with suppression of ERK activation, STAT3 activation and miR-155 upregulation, signals widely associated with SF pathogenesis. Surprisingly however, DNA methylome analysis of Naïve-, CIA- and ES-62-CIA-SF cohorts reveals that rather than simply preventing pathogenic rewiring of SFs, ES-62 induces further changes in DNA methylation under the inflammatory conditions pertaining in the inflamed joint, including targeting genes associated with ciliogenesis, to programme a novel "resolving" CIA-SF phenotype. In addition to introducing a previously unsuspected aspect of ES-62's mechanism of action, such unique behaviour signposts the potential for developing DNA methylation signatures predictive of pathogenesis and its resolution and hence, candidate mechanisms by which novel therapeutic interventions could prevent SFs from perpetuating joint inflammation and destruction in RA. Pertinent to these translational aspects of ES-62-behavior, small molecule analogues (SMAs) based on ES-62's active PC-moieties mimic the rewiring of SFs as well as the protection against joint disease in CIA afforded by the parasitic worm product.

Ozone in Medicine. The Low-Dose Ozone Concept and Its Basic Biochemical Mechanisms of Action in Chronic Inflammatory Diseases

Low-dose ozone acts as a bioregulator in chronic inflammatory diseases, biochemically characterized by high oxidative stress and a blocked regulation. During systemic applications, “Ozone peroxides” are able to replace H₂O₂ in its specific function of regulation, restore redox signaling, and improve the antioxidant capacity. Two different mechanisms have to be understood. Firstly, there is the direct mechanism, used in topical treatments, mostly via radical reactions. In systemic treatments, the indirect, ionic mechanism is to be discussed: “ozone peroxide” will be directly reduced by the glutathione system, informing the nuclear factors to start the regulation. The GSH/GSSG balance outlines the ozone dose and concentration limiting factor. Antioxidants are regulated, and in the case of inflammatory diseases up-regulated; cytokines are modulated, here downregulated. Rheumatoid arthritis RA as a model for chronic inflammation: RA, in preclinical and clinical trials, reflects the pharmacology of ozone in a typical manner: SOD (superoxide dismutase), CAT (catalase) and finally GSH (reduced glutathione) increase, followed by a significant reduction of oxidative stress. Inflammatory cytokines are downregulated. Accordingly, the clinical status improves. The pharmacological background investigated in a remarkable number of cell experiments, preclinical and clinical trials is well documented and published in internationally peer reviewed journals. This should encourage clinicians to set up clinical trials with chronic inflammatory diseases integrating medical ozone as a complement.

NOX1/NADPH oxidase is involved in the LPS-induced exacerbation of collagen-induced arthritis

We investigate as yet an unidentified role of NOX1, a non-phagocytic isoform of the superoxide-generating NADPH oxidase, in immune responses using Nox1-knockout mice (Nox1-KO). The transcripts of NOX1 was expressed in lymphoid tissues, including the spleen, thymus, bone marrow, and inguinal lymphoid nodes. When antibody production after ovalbumin (OVA) immunization was examined, no significant differences were observed in serum anti-OVA IgG levels between wild-type mice (WT) and Nox1-KO. In the experimental asthma, the infiltration of eosinophils and the Th2 cytokine response after the induction of asthma with OVA were similar between the two genotypes. However, the severity and incidence of experimental collagen-induced arthritis (CIA) following the administration of a low dose of endotoxin (LPS) were significantly lower in Nox1-KO. While neither serum levels of autoantibodies nor in vitro cytokine responses were affected by Nox1 deficiency, NOX1 mRNA levels in the spleen significantly increased after the LPS challenge. Among the spleen cells, remarkable LPS-induced upregulation of NOX1 was demonstrated in both CD11b+ monocytes/macrophages and CD11c+ dendritic cells, suggesting that LPS-inducible NOX1 in monocytes/macrophages/dendritic cells may modulate the development of experimental CIA. Therapeutic targeting of NOX1 may therefore control the onset and/or severity of arthritis which is exacerbated by bacterial infection.

Aryl hydrocarbon receptor (Ahr)-dependent Il-22 expression by type 3 innate lymphoid cells control of acute joint inflammation

The aryl hydrocarbon receptor (AHR) controls several inflammatory and metabolic pathways involved in various diseases, including the development of arthritis. Here, we investigated the role of AHR activation in IL-22-dependent acute arthritis using the K/BxN serum transfer model. We observed an overall reduction of cytokine expression in Ahr-deficient mice, along with decreased signs of joint inflammation. Conversely, we report worsened arthritis symptoms in Il-22 deficient mice. Pharmacological stimulation of AHR with the agonist VAG539, as well as injection of recombinant IL-22, given prior arthritogenic triggering, attenuated inflammation and reduced joint destruction. The protective effect of VAG539 was abrogated in Il-22 deficient mice. Finally, conditional Ahr depletion of Rorc-expressing cells was sufficient to attenuate arthritis, thereby uncovering a previously unsuspected role of AHR in type 3 innate lymphoid cells during acute arthritis.

ZIP8 exacerbates collagen-induced arthritis by increasing pathogenic T cell responses

Zinc is a trace element that is essential for immune responses. Therefore, changes in cellular zinc levels in specific immune cells may influence inflammatory autoimmune diseases, such as rheumatoid arthritis (RA). However, the regulation of zinc mobilization in immune cells and its role in the pathogenesis of RA are not fully understood. Thus, we investigated the roles of zinc transporters in RA pathogenesis. We demonstrated that ZIP8 was specifically upregulated in CD4+ T cells that infiltrated the inflamed joint and that ZIP8 deficiency in CD4+ T cells abrogated collagen-induced arthritis. ZIP8 deficiency dramatically affected zinc influx in effector T cells and profoundly reduced T cell receptor (TCR)-mediated signaling, including NF-κB and MAPK signaling, which are pathways that are involved in T helper (Th) 17 cell differentiation. Taken together, our findings suggest that ZIP8 depletion in CD4+ T cells attenuates TCR signaling due to insufficient cellular zinc, thereby reducing the function of effector CD4+ T cells, including Th17 cells. Our results also suggest that targeting ZIP8 may be a useful strategy to inhibit RA development and pathogenesis.

Regulation of inflammatory and catabolic responses to IL-1β in rat articular chondrocytes by microRNAs miR-122 and miR-451

OBJECTIVE

miR-122 stimulates proliferation of growth plate chondrocytes whereas miR-451 stimulates terminal differentiation and matrix turnover. Here, we examined the potential of these microRNA as regulators of articular chondrocytes using an in vitro model of osteoarthritis.

METHODS

miR-122 and miR-451 presence in rat articular cartilage was assessed using the anterior cruciate ligament transection model of OA. In vitro testing used first passage rat articular chondrocytes (rArCs) that were transfected with lipofectamine (Lipo) and miR-122 or miR-451 for 24-h, then treated with 10 ng/mL IL-1β in order to mimic an osteoarthritic environment. Conditioned media were collected and MMP13, PGE2 and OA-related cytokines were measured. Matrix vesicles were collected from cell layer lysates using ultra-centrifugation. Cells were treated with miR-122 or miR-451 inhibitors to verify miR-specific effects.

RESULTS

Both miR-122 and miR-451 were increased in the OA articular cartilage compared to healthy tissue; rArCs expressed both microRNAs in MVs. miR-122 prevented IL-1β-dependent increases in MMP-13 and PGE2, whereas miR-451 significantly increased the IL-1β effect. Multiplex data indicated that miR-122 reduced the stimulatory effect of IL-1β on IL-1α, IL-2, Il-4, IL-6, GM-CSF, MIP-1A, RANTES and VEGF. In contrast, IL-2, IL-4, IL-6, GM-CSF, and MIP-1A were increased by miR-451 while VEGF was decreased. Inhibiting miR-122 exacerbated the response to IL-1β indicating endogenous levels of miR-122 were present. There were no differences in MMP-13 or PGE2 with miR-451 Locked Nucleic Acid (LNA) inhibitor treatment.

CONCLUSIONS

Both miRs were elevated in OA in a rat bilateral anterior cruciate ligament transection (ACLT) model. miR-122 prevented, while miR-451 exacerbated the effects of IL-1β on rArCs.

Erythroid Differentiation Regulator 1 Ameliorates Collagen-Induced Arthritis via Activation of Regulatory T Cells

Erythroid differentiation regulator 1 (Erdr1) has been identified as an anti-inflammatory factor in several disease models, including collagen-induced arthritis (CIA), but its exact mechanisms are still not fully understood. Here, the involvement of regulatory T (Treg) cells in Erdr1-improved CIA was investigated. In the CIA model, Erdr1 was confirmed to reduce collagen-specific IgM in plasma and plasma cells in draining lymph nodes. Importantly, the downregulated Treg cell ratio in draining lymph nodes from CIA mice was recovered by Erdr1 treatment. In addition, administration of Erdr1 improved the CIA score and joint tissue damage, while it revealed no effect in Treg cell-depleted CIA mice, indicating that Treg cells mediate the therapeutic effects of Erdr1 in the CIA model. Results from in vitro experiments also demonstrated that Erdr1 significantly induced Treg cell differentiation and the expression of Treg activation markers, including CD25, CD69, and CTLA4 in CD4⁺Foxp3⁺ cells. Furthermore, Erdr1-activated Treg cells dramatically suppressed the proliferation of responder T cells, suggesting that they are functionally active. Taken together, these results show that Erdr1 induces activation of Treg cells and ameliorates rheumatoid arthritis via Treg cells.

Lubricin in experimental and naturally occurring osteoarthritis: a systematic review

OBJECTIVE

Lubricin is increasingly being evaluated as an outcome measure in studies investigating post-traumatic and naturally occurring osteoarthritis. However, there are discrepancies in results, making it unclear as to whether lubricin is increased, decreased or unchanged in osteoarthritis. The purpose of this study was to review all papers that measured lubricin in joint injury or osteoarthritis in order to draw conclusions about lubricin regulation in joint disease.

DESIGN

A systematic search of the Pubmed, Web of Knowledge, and EBSCOhost databases for papers was performed. Inclusion criteria were in vivo studies that measured lubricin in humans or animals with joint injury, that investigated lubricin supplementation in osteoarthritic joints, or that described the phenotype of a lubricin knock-out model. A methodological assessment was performed.

RESULTS

Sixty-two studies were included, of which thirty-eight measured endogenous lubricin in joint injury or osteoarthritis. Nineteen papers found an increase or no change in lubricin and nineteen reported a decrease. Papers that reported a decrease in lubricin were cited four times more often than those that reported an increase. Fifteen papers described lubricin supplementation, and all reported a beneficial effect. Eleven papers described lubricin knock-out models.

CONCLUSIONS

The human literature reveals similar distributions of papers reporting increased lubricin as compared to decreased lubricin in osteoarthritis. The animal literature is dominated by reports of decreased lubricin in the rat anterior cruciate ligament transection model, whereas studies in large animal models report increased lubricin. Intra-articular lubricin supplementation may be beneficial regardless of whether lubricin increases or decreases in OA.

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)-1β, 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.

Diacetylcurcumin: Its Potential Antiarthritic Effect on a Freund's Complete Adjuvant-Induced Murine Model

The present study aims to evaluate the antiarthritic activity of diacetylcurcumin (DAC), a synthetic derivative where the free phenolic groups of curcumin are derivatized by acetylation, thereby conferring greater lipophilicity to the parent molecule and partially overcoming the limited systemic bioavailability of curcumin. Antiarthritic activity was evaluated on a Freund’s complete adjuvant (FCA)-induced murine model of arthritis. Oral administration of DAC (60 and 120 mg/kg) resulted in a significant inhibition of inflammation in the acute and chronic phases, respectively, demonstrating an improved and sustained anti-inflammatory effect, comparable to that of curcumin (150 mg/kg) in the chronic stage at a lower dose. Phenylbutazone (80 mg/kg) was used as a reference drug. The pharmacological consequence of DAC or curcumin treatment is the prevention of secondary lesions commonly associated with this biological model.

Induction of Krüppel-like factor 2 reduces K/BxN serum-induced arthritis

Krüppel-like factor 2 (KLF2) critically regulates activation and function of monocyte, which plays important pathogenic role in progressive joint destruction in rheumatoid arthritis (RA). It is yet to be established the molecular basis of KLF2-mediated regulation of monocytes in RA pathogenesis. Herein, we show that a class of compound, HDAC inhibitors (HDACi) induced KLF2 expression in monocytes both in vitro and in vivo. KLF2 level was also elevated in tissues, such as bone marrow, spleen and thymus in mice after infusion of HDACi. Importantly, HDACi significantly reduced osteoclastic differentiation of monocytes with the up-regulation of KLF2 and concomitant down-regulation of matrixmetalloproteinases both in the expression level as well as in the protein level. In addition, HDACi reduced K/BxN serum-induced arthritic inflammation and joint destruction in mice in a dose-dependent manner. Finally, co-immunoprecipitation and overexpression studies confirmed that KLF2 directly interacts with HDAC4 molecule in cells. These findings provide mechanistic evidence of KLF2-mediated regulation of K/BxN serum-induced arthritic inflammation.

Necrostatin-1 ameliorates adjuvant arthritis rat articular chondrocyte injury via inhibiting ASIC1a-mediated necroptosis

Necroptosis, a necrotic cell death pathway regulated by receptor interacting protein (RIP) 1 and 3, plays a key role in pathophysiological processes, including rheumatoid arthritis (RA). However, whether necroptosis is involved in RA articular cartilage damage processes remain unclear. The aim of present study was to investigate the dynamic changes in arthritic chondrocyte necroptosis and the effect of RIP1 inhibitor necrostatin-1 (Nec-1) and acid-sensing ion channels (ASICs) inhibitor amiloride on arthritic cartilage injury and acid-induced chondrocyte necroptosis. Our results demonstrated that the expression of RIP1, RIP3 and mixed lineage kinase domain-like protein phosphorylation (p-MLKL) were increased in adjuvant arthritis (AA) rat articular cartilage in vivo and acid-induced chondrocytes in vitro. High co-expression of ASIC1a and RIP1 showed in AA rat articular cartilage. Moreover, Nec-1 and amiloride could reduce articular cartilage damage and necroinflammation in AA rats. In addition, acid-induced increase in necroptosis markers RIP1/RIP3 were inhibited by Nec-1, ASIC1a-specific blocker psalmotoxin-1 (PcTx-1) or ASIC1a-short hairpin RNA respectively, which revealed that necroptosis is triggered in acid-induced chondrocytes and mediated by ASIC1a. These findings indicated that blocking ASIC1a-mediated chondrocyte necroptosis may provide potential therapeutic strategies for RA treatment.

Microglial pannexin-1 channel activation is a spinal determinant of joint pain

Chronic joint pain such as mechanical allodynia is the most debilitating symptom of arthritis, yet effective therapies are lacking. We identify the pannexin-1 (Panx1) channel as a therapeutic target for alleviating mechanical allodynia, a cardinal sign of arthritis. In rats, joint pain caused by intra-articular injection of monosodium iodoacetate (MIA) was associated with spinal adenosine 5'-triphosphate (ATP) release and a microglia-specific up-regulation of P2X7 receptors (P2X7Rs). Blockade of P2X7R or ablation of spinal microglia prevented and reversed mechanical allodynia. P2X7Rs drive Panx1 channel activation, and in rats with mechanical allodynia, Panx1 function was increased in spinal microglia. Specifically, microglial Panx1-mediated release of the proinflammatory cytokine interleukin-1β (IL-1β) induced mechanical allodynia in the MIA-injected hindlimb. Intrathecal administration of the Panx1-blocking peptide ¹⁰panx suppressed the aberrant discharge of spinal laminae I-II neurons evoked by innocuous mechanical hindpaw stimulation in arthritic rats. Furthermore, mice with a microglia-specific genetic deletion of Panx1 were protected from developing mechanical allodynia. Treatment with probenecid, a clinically used broad-spectrum Panx1 blocker, resulted in a striking attenuation of MIA-induced mechanical allodynia and normalized responses in the dynamic weight-bearing test, without affecting acute nociception. Probenecid reversal of mechanical allodynia was also observed in rats 13 weeks after anterior cruciate ligament transection, a model of posttraumatic osteoarthritis. Thus, Panx1-targeted therapy is a new mechanistic approach for alleviating joint pain.

Smoking-induced aggravation of experimental arthritis is dependent of aryl hydrocarbon receptor activation in Th17 cells

BACKGROUND

Epidemiologic studies have highlighted the association of environmental factors with the development and progression of autoimmune and chronic inflammatory diseases. Among the environmental factors, smoking has been associated with increased susceptibility and poor prognosis in rheumatoid arthritis (RA). However, the immune and molecular mechanism of smoking-induced arthritis aggravation remains unclear. The transcription factor aryl hydrocarbon receptor (AHR) regulates the generation of Th17 cells, CD4 T cells linked the development of autoimmune diseases. AHR is activated by organic compounds including polycyclic aromatic hydrocarbons (PAHs), which are environmental pollutants that are also present in cigarette smoke. In this study, we investigated the role of AHR activation in the aggravation of experiment arthritis induced by exposure to cigarette smoke.

METHODS

Mice were exposed to cigarette smoke during the developmental phase of antigen-induced arthritis and collagen-induced arthritis to evaluate the effects of smoking on disease development. Aggravation of articular inflammation was assessed by measuring neutrophil migration to the joints, increase in articular hyperalgesia and changes in the frequencies of Th17 cells. In vitro studies were performed to evaluate the direct effects of cigarette smoke and PAH on Th17 differentiation. We also used mice genetically deficient for AHR (Ahr KO) and IL-17Ra (Il17ra KO) to determine the in vivo mechanism of smoking-induced arthritis aggravation.

RESULTS

We found that smoking induces arthritis aggravation and increase in the frequencies of Th17 cells. The absence of IL-17 signaling (Il17ra KO) conferred protection to smoking-induced arthritis aggravation. Moreover, in vitro experiments showed that cigarette smoke can directly increase Th17 differentiation of T cells by inducing AHR activation. Indeed, Ahr KO mice were protected from cigarette smoke-induced arthritis aggravation and did not display increase in TH17 frequencies, suggesting that AHR activation is an important mechanism for cigarette smoke effects on arthritis. Finally, we demonstrate that PAHs are also able to induce arthritis aggravation.

CONCLUSIONS

Our data demonstrate that the disease-exacerbating effects of cigarette smoking are AHR dependent and environmental pollutants with AHR agonist activity can induce arthritis aggravation by directly enhancing Th17 cell development.

Sulforaphane Modulates Joint Inflammation in a Murine Model of Complete Freund's Adjuvant-Induced Mono-Arthritis

Rheumatoid arthritis (RA) is characterized by inflammation of one or more joints, and affects ~1% of the adult population worldwide. Sulforaphane (SFN) is a natural compound that has been suggested as an antioxidant. Here, SFN’s effects were evaluated in a murine mono-arthritis model. Mono-arthritis was induced in mice by a single intra-articular injection of Complete Freund’s Adjuvant (CFA-10 µg/joint, in 10 µL) into the ipsilateral joint. The contralateral joint received an equal volume of PBS. On the 4th day post-joint inflammation induction, animals received either SFN (10 mg/kg) or vehicle (3% DMSO in saline), intraperitoneally (i.p.), twice a day for 3 days. Joint swelling and secondary mechanical allodynia and hyperalgesia were evaluated over 7 days post-CFA. After this period, animals were culled and their blood and synovial fluid samples were collected for analysis of cell populations, cytokine release and thioredoxin reductase (TrxR) activity. Knee joint samples were also collected for histology. SFN reduced joint swelling and damage whilst increasing the recruitment of Ly6C⁺ and Ly6G⁺ cells to CFA-injected joints. SFN-treated animals presented down-regulation of CD11b and CD62L on synovial fluid Ly6G⁺ cells. Synovial fluid samples obtained from CFA-injected joints and plasma samples of SFN-treated mice presented higher levels of IL-6 and increased activity of TrxR, in comparison with controls. These results indicate that SFN reduces knee joint damage by modulating cell activation/migration to the joints, cytokine production and increasing the activity of TrxR, and therefore, may represent an alternative treatment to joint inflammation.

Peripheral Mechanisms Contributing to Osteoarthritis Pain

PURPOSE OF REVIEW

Osteoarthritis (OA) is the most common form of arthritis and a major source of pain and disability worldwide. OA-associated pain is usually refractory to classically used analgesics, and disease-modifying therapies are still lacking. Therefore, a better understanding of mechanisms and mediators contributing to the generation and maintenance of OA pain is critical for the development of efficient and safe pain-relieving therapies.

RECENT FINDINGS

Both peripheral and central mechanisms contribute to OA pain. Clinical evidence suggests that a strong peripheral nociceptive drive from the affected joint maintains pain and central sensitization associated with OA. Mediators present in the OA joint, including nerve growth factor, chemokines, cytokines, and inflammatory cells can contribute to sensitization. Furthermore, structural alterations in joint innervation and nerve damage occur in the course of OA. Several interrelated pathological processes, including joint damage, structural reorganization of joint afferents, low-grade inflammation, neuroplasticity, and nerve damage all contribute to the pain observed in OA. It can be anticipated that elucidating exactly how these mechanisms are operational in the course of progressive OA may lead to the identification of novel targets for intervention.

In Vivo Models for Inflammatory Arthritis

In vivo mouse models of inflammatory arthritis are extensively used to investigate pathogenic mechanisms governing inflammation-driven joint damage. Two commonly utilized models include collagen-induced arthritis (CIA) and methylated bovine serum albumin (mBSA) antigen-induced arthritis (AIA). These offer unique advantages for modeling different aspects of human disease. CIA involves breach of immunological tolerance resulting in systemic autoantibody-driven arthritis, while AIA results in local resolving inflammatory flares and articular T cell-mediated damage. Despite limitations that apply to all animal models of human disease, CIA and AIA have been instrumental in identifying pathogenic mediators, immune cell subsets and stromal cell responses that determine disease onset, progression, and severity. Moreover, these models have enabled investigation of disease phases not easily studied in patients and have served as testing beds for novel biological therapies, including cytokine blockers and small molecule inhibitors of intracellular signaling that have revolutionized rheumatoid arthritis treatment.

Establishment of rat ankle post-traumatic osteoarthritis model induced by malleolus fracture

BACKGROUND

Malleolar fracture, which is present in 37-53% of human ankle osteoarthritis (OA), is the most common type of fracture in the ankle joint. In spite of this, no rat animal model has been developed for this type of injury to date. Here, we established a rat ankle post-traumatic OA (PTOA) model induced by malleolar fracture; this model will be useful in ankle OA research.

METHODS

Two-month-old male Sprague Dawley (SD) rats were randomized into 2 groups (n = 19 per group): 1) malleolus articular fracture, dislocation, and immediate reduction on the right joints and 2) malleolus articular fracture on the right ankle. The contralateral ankle joints were used as controls. The fracture and healing processes were confirmed and monitored by radiography. Changes in inflammation were monitored in vivo by fluorescence molecular tomography (FMT). Cartilage damage and changes in expression of OA-related genes were analyzed by histology, immunohistochemistry, Real-time quantitative PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA) at 8 weeks post-surgery.

RESULTS

X-rays showed that all fractures were healed at 8 weeks post-surgery. A reproducible, mild to moderate degree of OA cartilage damage with reduced aggrecan was detected by histology in all animals in both groups but there was no significant difference between the two groups. Decreased Col-II and increased Col-X and MMP-13 levels were detected by qPCR, immunohistochemistry, ELISA and FMT from both groups cartilage.

CONCLUSIONS

Malleolus articular fracture alone induces ankle OA with lesions on the central weight bearing area of the tibiotalar joint in rats. This model will provide a reproducible and useful tool for researchers to study ankle OA.

Experimental colitis delays and reduces the severity of collagen-induced arthritis in mice

Amongst extraintestinal manifestations (EIM) occurring in IBD patients, rheumatologic manifestations are the most frequent. Understanding the relationships between arthritis and colitis is a prerequisite to improving the management of these patients. Microbiota of patients with IBD or rheumatologic diseases, like spondyloarthritis (SpA) is modified compared to healthy individual. Thus, we have evaluated the impact of colitis in the development of arthritis in mice and we have analyzed microbiota changes. Collagen-induced arthritis (CIA) was induced at day 0 in DBA1 mice exposed or not to Dextran Sodium Sulfate (DSS) to induce colitis between day 14 and day 21. Animals were monitored regularly for arthritis and colitis severity (clinical score, hindpaw edema). Fecal microbiota was studied by 16S rRNA deep sequencing at critical time points (D14, D14, D21 & D41). At day 41, histological scoring of the intestines and ankles were performed at the end of experiment. Induction of colitis slightly delayed arthritis onset (2 ± 1 days of delay) and reduced its severity (5.75 ± 1.62 in arthritis only group vs 4.00 ± 1.48 in arthritis + colitis group (p = 0.02 at day 28) macroscopically and histologically. In contrast, colitis severity was not influenced by arthritis development. Induction of colitis promoted a modification of microbiota composition and a decrease of α-diversity. Fecal microbiota composition was different between “colitis” and “arthritis+colitis” groups during colitis development. Interestingly a milder decrease of bacterial diversity in the “arthritis+colitis” group was observed. Concomitant experimental colitis protects mice against collagen-induced arthritis and this is associated with changes in gut microbiome composition.

Therapeutic Effect of Exogenous Truncated IK Protein in Inflammatory Arthritis

Inhibitor K562 (IK) protein was first isolated from the culture medium of K562, a leukemia cell line. It is known to be an inhibitory regulator of interferon-γ-induced major histocompatibility complex class (MHC) II expression. Previously, we found that transgenic (Tg) mice constitutively expressing truncated IK (tIK) showed reduced numbers of pathogenic Th1 and Th17 cells, which are known to be involved in the development of rheumatoid arthritis (RA). Here, we investigated whether exogenous tIK protein has a therapeutic effect in arthritis in disease models and analyzed its mechanism. Exogenous tIK protein was produced in an insect expression system and applied to the collagen antibody-induced arthritis (CAIA) mouse disease model. Injection of tIK protein alleviated the symptoms of arthritis in the CAIA model and reduced Th1 and Th17 cell populations. In addition, treatment of cultured T cells with tIK protein induced expression of A20, a negative regulator of nuclear factor-κB (NFκB)-induced inflammation, and reduced expression of several transcription factors related to T cell activation. We conclude that exogenous tIK protein has the potential to act as a new therapeutic agent for RA patients, because it has a different mode of action to biopharmaceutical agents, such as tumor necrosis factor antagonists, that are currently used to treat RA.

Combination Therapy of PEG-HM-3 and Methotrexate Retards Adjuvant-Induced Arthritis

At present, the early phenomenon of inflammatory angiogenesis is rarely studied in Rheumatoid arthritis (RA). Previous research found that PEG-HM-3, an integrin inhibitor, possessed anti-angiogenesis and anti-rheumatic activity. In this study, the advantages of inhibiting angiogenesis and immune cell adhesion and migration, as well as the benefits of anti-arthritis effects, were evaluated using a combination of PEG-HM-3 and methotrexate (MTX). In vitro, spleen cell proliferation and the levels of tumor necrosis factor α (TNF-α) in macrophage supernatant were assessed. Hind paw edema, arthritis index, clinical score, body weight and immunohistochemistry (IHC) of the spleen, thymus, and joint cavity were evaluated in vivo in adjuvant-induced arthritis rats. Joints of the left hind paws were imaged by X-ray. The expression of the toll-like receptor 4 (TLR-4) protein was assessed in lipopolysaccharide (LPS)-induced synoviocytes. PEG-HM-3 combined with MTX significantly reduced primary and secondary swelling of the hind paws, the arthritis index, the clinical score and bone erosion. The results of IHC showed that the levels of interleukin-6 (IL-6) in spleens and the levels of TNF-α, CD31 (cluster of differentiation 31), and CD105 in the joint cavity were decreased. The body weight of rats was maintained during combination therapy. Ankle cavity integrity, and bone erosion and deformity were improved in combination treatment. The expression of TLR-4 was significantly reduced with combination treatment in rat synoviocytes. Co-suppression of both inflammation and angiogenesis in arthritis was achieved in this design with combination therapy. The activity of nuclear transcription factor (NF-κB) and the expression of inflammatory factors were down regulated via integrin αvβ₃ and TLR-4 signaling pathways. In the future, the application of this combination can be a candidate in early and mid-term RA therapy.

Models to define the stages of articular cartilage degradation in osteoarthritis development

Osteoarthritis (OA) is a common chronic disorder that affects an increasing number of the ageing population. Despite the prevalence, there are currently no therapies. Defining new therapies that target specific pathogenic phases of disease development relies on the effective separation of the different stages of OA. This manuscript reviews the tissues and models that are being used to separate these stages of disease, in particular initiation and early and late progression. These models include human tissues with known initiating factors, the use of anatomical locations with defined relationships to the primary cartilage lesion area, timing of OA development in well-described animal models and the versatility of a non-invasive model of murine knee joint trauma.

Loss of IL-22 inhibits autoantibody formation in collagen-induced arthritis in mice

Interleukin 22 (IL-22) expression is associated with increased joint destruction and disease progression in rheumatoid arthritis (RA). Although IL-22 is considered a pro-inflammatory cytokine, its mechanism of action in RA remains incompletely understood. Here, we used the collagen-induced arthritis model in IL-22 deficient (IL-22(-/-) ) mice to study the role of IL-22 in RA. In spite of normal disease incidence, disease severity is significantly diminished in IL-22(-/-) mice. Moreover, pathogenicity of Th17 cells and development and function of B cells are unaffected. In contrast, splenic plasma cells, as well as serum autoantibody titers, are reduced in the absence of IL-22. At the peak of disease, germinal centers (GCs) are severely reduced in the spleens of IL-22(-/-) mice, correlating with a decline in GC B-cell numbers. Within the GC, we identified IL-22R1 expressing follicular dendritic cell-like stromal cells. Human lymphoid stromal cells respond to IL-22 ex vivo by inducing transcription of CXCL12 and CXCL13. We therefore postulate IL-22 as an important enhancer of the GC reaction, maintaining chemokine levels for the persistence of GC reactions, essential for the production of autoantibody-secreting plasma cells. Blocking IL-22 might therefore prevent immune-complex deposition and destruction of joints in RA patients.

Intra-Articular Injections of Polyphenols Protect Articular Cartilage from Inflammation-Induced Degradation: Suggesting a Potential Role in Cartilage Therapeutics

Arthritic diseases, such as osteoarthritis and rheumatoid arthritis, inflict an enormous health care burden on society. Osteoarthritis, a degenerative joint disease with high prevalence among older people, and rheumatoid arthritis, an autoimmune inflammatory disease, both lead to irreversible structural and functional damage to articular cartilage. The aim of this study was to investigate the effect of polyphenols such as catechin, quercetin, epigallocatechin gallate, and tannic acid, on crosslinking type II collagen and the roles of these agents in managing in vivo articular cartilage degradation. The thermal, enzymatic, and physical stability of bovine articular cartilage explants following polyphenolic treatment were assessed for efficiency. Epigallocatechin gallate and tannic acid-treated explants showed >12 °C increase over native cartilage in thermal stability, thereby confirming cartilage crosslinking. Polyphenol-treated cartilage also showed a significant reduction in the percentage of collagen degradation and the release of glycosaminoglycans against collagenase digestion, indicating the increase physical integrity and resistance of polyphenol crosslinked cartilage to enzymatic digestion. To examine the in vivo cartilage protective effects, polyphenols were injected intra-articularly before (prophylactic) and after (therapeutic) the induction of collagen-induced arthritis in rats. The hind paw volume and histomorphological scoring was done for cartilage damage. The intra-articular injection of epigallocatechin gallate and tannic acid did not significantly influence the time of onset or the intensity of joint inflammation. However, histomorphological scoring of the articular cartilage showed a significant reduction in cartilage degradation in prophylactic- and therapeutic-groups, indicating that intra-articular injections of polyphenols bind to articular cartilage and making it resistant to degradation despite ongoing inflammation. These studies establish the value of intra-articular injections of polyphenol in stabilization of cartilage collagen against degradation and indicate the unique beneficial role of injectable polyphenols in protecting the cartilage in arthritic conditions.

Experimental osteoarthritis model by means of medial meniscectomy in rats and effects of diacerein administration and hyaluronic acid injection

CONTEXT AND OBJECTIVE

The development of a slow and progressive mechanical model for osteoarthritis is important for correlation with clinical practice, and for evaluating the effects of disease-modifying medications. A mechanical osteoarthritis model was developed to evaluate the effects of intra-articular hyaluronic acid (HA) injection and oral diacerein administration.

DESIGN AND SETTING

Experimental study at the Department of Orthopedics and Traumatology, Universidade de São Paulo.

METHOD

Total medial meniscectomy was performed on seven groups of ten Wistar rats each, comprising four control groups (C) and three study groups (S). C.I: operated, non-medicated; C.II: operated, injections of HA vehicle; C.III: non-operated, non-medicated; C.IV: operated, non-medicated, sacrificed three months post-meniscectomy; S.I: operated, receiving intra-articular HA injections; S.II: operated, oral diacerein from the third to the seventh postoperative month; S.III: operated, received both medications. All the animals (except C.IV) were sacrificed seven months post-meniscectomy. All femurs and tibias were assessed histologically.

RESULTS

The most severe degenerative histological changes were in the tibias of the operated knees. On the contralateral side, all groups had mild changes on the tibial surface. The femoral surface had slight changes. C.I showed severe changes. S.II results matched those of C.IV. HA protected the tibial surface. S.II and S.III had similar results.

CONCLUSIONS

1) The experimental model produced mild arthritis after three months and severe arthritis after seven months; 2) diacerein reduced the degenerative changes in both knees; 3) HA protected the joint cartilage; 4) Combining the two drugs did not improve the results.

Hypoxia-inducible factor-2α is an essential catabolic regulator of inflammatory rheumatoid arthritis

Hypoxia-inducible factor-2α (HIF-2α) is sufficient to cause experimental rheumatoid arthritis and acts to regulate the functions of fibroblast-like cells from tissue surrounding joints, independent of HIF-1α.

Rheumatoid arthritis (RA) is a systemic autoimmune disorder that manifests as chronic inflammation and joint tissue destruction. However, the etiology and pathogenesis of RA have not been fully elucidated. Here, we explored the role of the hypoxia-inducible factors (HIFs), HIF-1α (encoded by HIF1A) and HIF-2α (encoded by EPAS1). HIF-2α was markedly up-regulated in the intimal lining of RA synovium, whereas HIF-1α was detected in a few cells in the sublining and deep layer of RA synovium. Overexpression of HIF-2α in joint tissues caused an RA-like phenotype, whereas HIF-1α did not affect joint architecture. Moreover, a HIF-2α deficiency in mice blunted the development of experimental RA. HIF-2α was expressed mainly in fibroblast-like synoviocytes (FLS) of RA synovium and regulated their proliferation, expression of RANKL (receptor activator of nuclear factor–κB ligand) and various catabolic factors, and osteoclastogenic potential. Moreover, HIF-2α–dependent up-regulation of interleukin (IL)-6 in FLS stimulated differentiation of T_H17 cells—crucial effectors of RA pathogenesis. Additionally, in the absence of IL-6 (Il6^−/− mice), overexpression of HIF-2α in joint tissues did not cause an RA phenotype. Thus, our results collectively suggest that HIF-2α plays a pivotal role in the pathogenesis of RA by regulating FLS functions, independent of HIF-1α.

Rheumatoid arthritis (RA) is a systemic autoimmune disorder characterized by chronic inflammation in joint tissues leading to destruction of cartilage and bone. Despite some therapeutic advances, the etiology of RA pathogenesis is not yet clear, and effective treatment of RA remains a significant, unmet medical need. Hypoxia is a prominent feature of inflamed tissue within RA-affected joints, and earlier work has implicated limited involvement of hypoxia-inducible factor (HIF)-1 α. We explored the role of a second HIF family member, HIF-2α, in RA pathogenesis. We showed that HIF-2α is markedly increased in the tissue lining the RA-affected joints. Notably and in contrast to HIF-1α, when overexpressed in normal mouse joint tissues, HIF-2α is sufficient to cause RA-like symptoms. Conversely, an HIF-2α deficiency blocks the development of experimental arthritis in mice. We discovered further that HIF-2α regulates RA pathogenesis by modulating various RA-associated functions of joint-specific fibroblast-like cells, including proliferation, expression of cytokines, chemokines, and matrix-degrading enzymes, and bone-remodeling potential. HIF-2α also increases the ability of these cells to promote interleukin-6–dependent differentiation of T_H17 cells, a known effector of RA pathogenesis. We thus show that HIF-1α and HIF-2α have distinct roles and act via different mechanisms in RA pathogenesis.

Myeloid deletion of SIRT1 aggravates serum transfer arthritis in mice via nuclear factor-κB activation

Objective

SIRT1 modulates the acetylation of the p65 subunit of nuclear factor-κB (NF-κB) and plays a pivotal role in the inflammatory response. This study sought to assess the role of SIRT1 in rheumatoid arthritis (RA) using a myeloid cell-specific SIRT1 knockout (mSIRT1 KO) mouse.

Methods

mSIRT1 KO mice were generated using the loxP/Cre recombinase system. K/BxN serum transfer arthritis was induced in mSIRT1 KO mice and age-matched littermate loxP control mice. Arthritis severity was assessed by clinical and pathological scoring. The levels of inflammatory cytokines in the serum and joints were measured by ELISA. Migration, M1 polarization, cytokine production, osteoclastogenesis, and p65 acetylation were assessed in bone marrow-derived monocytes/macrophages (BMMs).

Results

mSIRT1 KO mice showed more severe inflammatory arthritis and aggravated pathological findings than control mice. These effects were paralleled by increases in IL-1, TNF-α, TRAP-positive osteoclasts, and F4/80⁺ macrophages in the ankles of mSIRT1 KO mice. In addition, BMMs from mSIRT1 KO mice displayed hyperacetylated p65 and increased NF-κB binding activity when compared to control mice, which resulted in increased M1 polarization, migration, pro-inflammatory cytokine production, and osteoclastogenesis.

Conclusion

Our study provides in vivo evidence that myeloid cell-specific deletion of SIRT1 exacerbates inflammatory arthritis via the hyperactivation of NF-κB signaling, which suggests that SIRT1 activation may be beneficial in the treatment of inflammatory arthritis.

Pain assessment in animal models of osteoarthritis

Assessment of pain in animal models of osteoarthritis is integral to interpretation of a model's utility in representing the clinical condition, and enabling accurate translational medicine. Here we describe behavioral pain assessments available for small and large experimental osteoarthritic pain animal models.

β-Glucan Derived from Zymosan Acts as an Adjuvant for Collagen-Induced Arthritis

Collagen-induced arthritis (CIA) is an experimental model of rheumatoid arthritis (RA) and has helped researchers to analyze the pathogenesis of inflammatory joint disease. In classical CIA, Freund's complete adjuvant (FCA), which contains heat-killed Mycobacterium tuberculosis, is used as an adjuvant. In our previous study, we reported that particles of beta-glucan, OX-CA, derived from Candida albicans, acted as a proper adjuvant in the CIA model. In this study, to establish pure beta-glucan as an adjuvant for CIA, we tested a commercially available preparation of Zymosan A (ZYM) and modified its products. beta-Glucan fractions of ZYM were prepared by oxidation with various concentrations of NaClO. The oxidized ZYM (OX-ZYM) was mainly composed of beta-glucan. In this study, we examined its effect as an adjuvant for CIA. DBA/1 mice injected with CII and OX-CA developed arthritis 7-10 days after receiving booster injections; the OX-ZYM fractions induced arthritis with the same time course. 0.01% OX-ZYM (oxidized with a 0.01% NaClO solution) caused arthritis faster than 0.1% OX-ZYM or 0.5% OX-ZYM. In conclusion, beta-glucan derived from ZYM by brief oxidation with NaClO is a suitable adjuvant for a CIA model with anti-CII antibody production.

Non-terminal animal model of post-traumatic osteoarthritis induced by acute joint injury

OBJECTIVE

Develop a non-terminal animal model of acute joint injury that demonstrates clinical and morphological evidence of early post-traumatic osteoarthritis (PTOA).

METHODS

An osteochondral (OC) fragment was created arthroscopically in one metacarpophalangeal (MCP) joint of 11 horses and the contralateral joint was sham operated. Eleven additional horses served as unoperated controls. Every 2 weeks, force plate analysis, flexion response, joint circumference, and synovial effusion scores were recorded. At weeks 0 and 16, radiographs (all horses) and arthroscopic videos (OC injured and sham joints) were graded. At week 16, synovium and cartilage biopsies were taken arthroscopically from OC injured and sham joints for histologic evaluation and the OC fragment was removed.

RESULTS

OC fragments were successfully created and horses were free of clinical lameness after fragment removal. Forelimb gait asymmetry was observed at week 2 (P = 0.0012), while joint circumference (P < 0.0001) and effusion scores (P < 0.0001) were increased in injured limbs compared to baseline from weeks 2 to 16. Positive flexion response of injured limbs was noted at multiple time points. Capsular enthesophytes were seen radiographically in injured limbs. Articular cartilage damage was demonstrated arthroscopically as mild wear-lines and histologically as superficial zone chondrocyte death accompanied by mild proliferation. Synovial hyperemia and fibrosis were present at the site of OC injury.

CONCLUSION

Acute OC injury to the MCP joint resulted in clinical, imaging, and histologic changes in cartilage and synovium characteristic of early PTOA. This model will be useful for defining biomarkers of early osteoarthritis and for monitoring response to therapy and surgery.

Analysis of adipose tissues and stromal vascular cells in a murine arthritis model

PURPOSE

Changes in body composition in rheumatoid arthritis (RA), including a reduction in skeletal muscle mass and the accumulation of visceral fat, have been identified, and the interaction between immune abnormality and metabolic disorders has received much attention. The effect of a high-fat (HF) diet and the role of adipose tissue in an arthritis model were investigated.

METHODS

The effect of an HF diet on the histopathology of joints in murine type II collagen-induced arthritis (CIA) was evaluated. The morphology and adipokine production of adipose tissues were analyzed, and macrophages in the stromal vascular fraction (SVF) were counted by flow cytometry. Serum adipokine levels were measured by ELISA.

RESULTS

Significant exacerbation of joint destruction and aggravated pathological conditions were observed in CIA mice that were fed an HF diet. However, the boundary length of adipose tissue tended to decrease and the levels of adipokines (leptin and adiponectin) were lowered by the induction of arthritis. In HF/CIA mice, nevertheless, the production of MCP-1 in adipose tissues and the accumulation of macrophages in the SVF were significantly higher than CON/CIA group. The serum leptin/adiponectin (L/A) ratio was positively correlated with the number of macrophages in the SVF and MCP-1 production by adipose tissue, particularly in the CIA group.

CONCLUSION

Functional alterations of adipose tissues could be originated from HF diet during developing arthritis. An abnormal activation of macrophages and an increased production of MCP-1 in adipose tissues might be both involved in joint destruction and inflammation.

11β-Hydroxysteroid dehydrogenase type 1, but not type 2, deficiency worsens acute inflammation and experimental arthritis in mice

Glucocorticoids profoundly influence immune responses, and synthetic glucocorticoids are widely used clinically for their potent antiinflammatory effects. Endogenous glucocorticoid action is modulated by the two isozymes of 11β-hydroxysteroid dehydrogenase (11β-HSD). In vivo, 11β-HSD1 catalyzes the reduction of inactive cortisone or 11-dehydrocorticosterone into active cortisol or corticosterone, respectively, thereby increasing intracellular glucocorticoid levels. 11β-HSD2 catalyzes the reverse reaction, inactivating intracellular glucocorticoids. Both enzymes have been postulated to modulate inflammatory responses. In the K/BxN serum transfer model of arthritis, 11β-HSD1-deficient mice showed earlier onset and slower resolution of inflammation than wild-type controls, with greater exostoses in periarticular bone and, uniquely, ganglion cysts, consistent with greater inflammation. In contrast, K/BxN serum arthritis was unaffected by 11β-HSD2 deficiency. In a distinct model of inflammation, thioglycollate-induced sterile peritonitis, 11β-HSD1-deficient mice had more inflammatory cells in the peritoneum, but again 11β-HSD2-deficient mice did not differ from controls. Additionally, compared with control mice, 11β-HSD1-deficient mice showed greater numbers of inflammatory cells in pleural lavages in carrageenan-induced pleurisy with lung pathology consistent with slower resolution. These data suggest that 11β-HSD1 limits acute inflammation. In contrast, 11β-HSD2 plays no role in acute inflammatory responses in mice. Regulation of local 11β-HSD1 expression and/or delivery of substrate may afford a novel approach for antiinflammatory therapy.

Etiological role of cigarette smoking in rheumatoid arthritis: Nasal exposure to cigarette smoke condensate extracts augments the development of collagen-induced arthritis in mice

Cigarette smoking is a major environmental risk factor for rheumatoid arthritis (RA). However, the experimental bases supporting the etiological role of cigarette smoking in RA have not been fully provided. We have reported that cigarette smoke condensate (CSC), by means of subcutaneous injection into DBA/1J mice with collagen and complete Freund's adjuvant or intraperitoneal injection one day before immunization, augmented the development of arthritis in the mouse model of collagen type II-induced arthritis (CIA). However, these experimental procedures may not be appropriate for cigarette smoking. In this study, we nasally exposed mice to mainstream CSC and found that CSC augmented the induction and development of arthritis and antibody level against collagen. Histological examination confirmed the augmenting effect of CSC. These findings provide experimental bases supporting the etiological role of cigarette smoking in RA.

Kinetic analysis of synovial signalling and gene expression in animal models of arthritis

BACKGROUND

Animal models of arthritis are frequently used to evaluate novel therapeutic agents. However, their ability to predict responses in humans is variable.

OBJECTIVE

To examine the time course of signalling molecule and gene expression in two models of arthritis to assist with selection of the model and timing of drug administration.

METHODS

The passive K/BxN serum transfer and collagen-induced arthritis (CIA) models were studied. Activation of MAP kinase and interferon (IFN)-response pathways was evaluated by quantitative PCR and western blot analysis of ankle joints at various time points during the models.

RESULTS

The kinetics of gene expression and kinase phosphorylation were strikingly different in passive K/BxN and CIA. All three MAP kinases (ERK, JNK and p38) and upstream kinases were activated within days in passive K/BxN and declined as arthritis severity decreased. Surprisingly, IFN-regulated genes, including IRF7, were not induced in the model. In CIA, activation of ERK and JNK was surprisingly low and p38 phosphorylation mainly peaked late in the disease. IFN-response genes were activated during CIA, with especially prominent peaks at the onset of clinical arthritis.

CONCLUSIONS

Timing of treatment and selection of CIA or passive K/BxN might have an important impact on therapeutic response. p38, in particular, increases during the late stages of CIA. ERK and JNK patterns are similar in passive K/BxN and rheumatoid arthritis (RA), while IFN-response genes in CIA and RA are similar. The dichotomy between RA and animal models could help explain the poor correlation between efficacy in RA and preclinical studies.

Use of routine clinical multimodality imaging in a rabbit model of osteoarthritis--part II: bone mineral density assessment

OBJECTIVE

To assess bone mineral density (BMD) at different depths from the articular surface in vivo and temporally in a rabbit model of osteoarthritis (OA) using clinical computed tomography (CT) equipment.

METHODS

The knee joints of rabbits (N=10 with Anterior cruciate ligament transection (ACLT) and contralateral sham joints, and N=6 unoperated controls) were scanned in a transverse image plane with a single-slice helical CT scanner. BMD was calculated at defined depths from the articular surface to the growth plate in the lateral femoral condyle (LFC), medial femoral condyle (MFC), lateral tibial plateau (LTP) and medial tibial plateau (MTP). Baseline BMD was measured at 2 weeks before surgery, and then repeated at weeks 2, 4 and 8 post-surgery in all 10 operated rabbits, and again at week 12 in five of the operated rabbits and at weeks -2 and 8 in the six control rabbits.

RESULTS

In the control joints, BMD decreased with increasing distance into the epiphysis and remained stable over time within each depth. A significant reduction in BMD was observed at week 2 post-operatively in three compartments (LFC, MFC and MTP) in the ACLT joints and persisted to week 12. A modest reduction in BMD occurred in the LTP and MTP of the sham joints at week 12 alone.

CONCLUSION

Clinical CT equipment permitted rapid, repeated, in vivo, non-invasive BMD assessment in a rabbit model of OA. A marked BMD reduction was measured with progression of OA until the end point at 12 weeks.

Collagen-induced arthritis

The collagen-induced arthritis (CIA) mouse model is the most commonly studied autoimmune model of rheumatoid arthritis. Autoimmune arthritis is induced in this model by immunization with an emulsion of complete Freund's adjuvant and type II collagen (CII). This protocol describes the steps necessary for acquisition, handling and preparation of CII, as well as selection of mouse strains, proper immunization technique and evaluation of the arthritis incidence and severity. Typically, the first signs of arthritis appear in this model 21-28 days after immunization, and identification of the arthritic limbs is not difficult. Using the protocol described, the investigator should be able to reproducibly induce a high incidence of CIA in various strains of genetically susceptible mice as well as learn how to critically evaluate the pathology of the disease. The total time for the preparation of reagents and the immunization of ten mice is about 1.5 h.

Macrophages and their products in rheumatoid arthritis

PURPOSE OF REVIEW

Macrophages differentiate from peripheral-blood monocytes. Both monocytes and synovial macrophages are key players in rheumatoid arthritis. These cells are involved in the initiation and perpetuation of inflammation, leukocyte adhesion and migration, matrix degradation and angiogenesis. Macrophages express adhesion molecules, chemokine receptors and other surface antigens. They also secrete a number of chemokines, cytokines, growth factors, proteases and other mediators.

RECENT FINDINGS

Macrophage migration-inhibitory factor has drawn significant attention recently. This cytokine is involved in macrophage activation and cytokine production. Migration-inhibitory factor also regulates glucocorticoid sensitivity and may be a pathogenic link between rheumatoid arthritis and atherosclerosis. Novel macrophage-derived chemokines and chemokine receptors have been identified. Interleukin-10 may have several proinflammatory effects that may influence its action in rheumatoid arthritis. Several proteinases including cathepsin G are produced by macrophages during rheumatoid arthritis-associated inflammatory and angiogenic events. Antirheumatic drugs, imatinib, chemokine receptor inhibitors and other specific strategies may become included in the therapy of rheumatoid arthritis.

SUMMARY

Macrophages and their products are key players in the pathogenesis of rheumatoid arthritis and may be good therapeutic targets.

Update on cytokines in rheumatoid arthritis

PURPOSE OF REVIEW

There have recently been fewer publications describing novel cytokines in rheumatoid arthritis. In the present review we focus on cytokines not previously implicated in contributing to the pathogenesis of rheumatoid arthritis.

RECENT FINDINGS

The detection of IL-17 and factors that drive the differentiation and expansion of ThIL-17 cells, particularly in mouse models, clearly place IL-17 as a potential therapeutic target in rheumatoid arthritis. The emergence of other novel cytokines, notably IL-20 and IL-22, is of interest, not least by displaying proinflammatory effects particularly on fibroblasts - in contrast to their family member IL-10, the most potent anti-inflammatory cytokine. IL-32 is also of interest, with proinflammatory effects both on myeloid and nonmyeloid cells.

SUMMARY

It is unclear whether the novel cytokines described in the present review will influence clinical practise. The involvement of IL-17 in murine arthritis may not translate as effectively to human arthritis - the ultimate test is a clinical trial in humans. The lack of efficacy of a recent anti-MCP-1/CCL-2 trial in rheumatoid arthritis highlights this dilemma. Finally, while technological advances including microarray analysis have broadened the scope for cytokine detection in rheumatoid arthritis, these methods have yet to translate to therapy in the clinic.

Global analyses of gene expression in early experimental osteoarthritis

OBJECTIVE

To analyze genome-wide changes in chondrocyte gene expression in a surgically induced model of early osteoarthritis (OA) in rats, to assess the similarity of this model to human OA, and to identify genes and mechanisms leading to OA pathogenesis.

METHODS

OA was surgically induced in 5 rats by anterior cruciate ligament transection and partial medial meniscectomy. Sham surgery was performed in 5 additional animals, which were used as controls. Both groups underwent 4 weeks of forced mobilization, 3 times per week. RNA was extracted directly from articular chondrocytes in the OA (operated), contralateral, and sham-operated knees. Affymetrix GeneChip expression arrays were used to assess genome-wide changes in gene expression. Expression patterns of selected dysregulated genes, including Col2a1, Mmp13, Adamts5, Ctsc, Ptges, and Cxcr4, were validated by real-time polymerase chain reaction, immunofluorescence, or immunohistochemistry 2, 4, and 8 weeks after surgery.

RESULTS

After normalization, comparison of OA and sham-operated samples showed 1,619 differentially expressed probe sets with changes in their levels of expression > or = 1.5-fold, 722 with changes > or = 2-fold, 135 with changes > or = 4-fold, and 20 with changes of 8-fold. Dysregulated genes known to be involved in human OA included Mmp13, Adamts5, and Ptgs2, among others. Several dysregulated genes (e.g., Reln, Phex, and Ltbp2) had been identified in our earlier microarray study of hypertrophic chondrocyte differentiation. Other genes involved in cytokine and chemokine signaling, including Cxcr4 and Ccl2, were identified. Changes in gene expression were also observed in the contralateral knee, validating the sham operation as the appropriate control.

CONCLUSION

Our results demonstrate that the animal model mimics gene expression changes seen in human OA, supporting the relevance of newly identified genes and pathways to early human OA. We propose new avenues for OA pathogenesis research and potential targets for novel OA treatments, including cathepsins and cytokine, chemokine, and growth factor signaling pathways, in addition to factors controlling the progression of chondrocyte differentiation.

T cell self-reactivity forms a cytokine milieu for spontaneous development of IL-17+ Th cells that cause autoimmune arthritis

This report shows that highly self-reactive T cells produced in mice as a result of genetically altered thymic T cell selection spontaneously differentiate into interleukin (IL)-17–secreting CD4⁺ helper T (Th) cells (Th17 cells), which mediate an autoimmune arthritis that clinically and immunologically resembles rheumatoid arthritis (RA). The thymus-produced self-reactive T cells, which become activated in the periphery via recognition of major histocompatibility complex/self-peptide complexes, stimulate antigen-presenting cells (APCs) to secrete IL-6. APC-derived IL-6, together with T cell–derived IL-6, drives naive self-reactive T cells to differentiate into arthritogenic Th17 cells. Deficiency of either IL-17 or IL-6 completely inhibits arthritis development, whereas interferon (IFN)-γ deficiency exacerbates it. The generation, differentiation, and persistence of arthritogenic Th17 cells per se are, however, insufficient for producing overt autoimmune arthritis. Yet overt disease is precipitated by further expansion and activation of autoimmune Th17 cells, for example, via IFN-γ deficiency, homeostatic proliferation, or stimulation of innate immunity by microbial products. Thus, a genetically determined T cell self-reactivity forms a cytokine milieu that facilitates preferential differentiation of self-reactive T cells into Th17 cells. Extrinsic or intrinsic stimuli further expand these cells, thereby triggering autoimmune disease. Intervention in these events at cellular and molecular levels is useful to treat and prevent autoimmune disease, in particular RA.

Cartilage oligomeric matrix protein (COMP) is modified by intra-articular liposomal clodronate in an experimental model of arthritis

OBJECTIVE

High-dose liposomal bisphosphonates exert apoptotic effects. This work studies the chondroprotective and anti-inflammatory properties of intra-articularly administered low-dose, non-cytotoxic liposomal clodronate.

METHODS

Antigen induced arthritis in rabbits was treated with intra-articular injections of liposomal clodronate. Drug effects on cartilage oligomeric matrix protein COMP was assessed using immunohistochemistry and morphometry of synovial membrane and hyaline articular cartilage.

RESULTS

COMP remained close to normal in liposomal clodronate treated superficial articular cartilage compared to a significant loss of COMP in arthritis controls treated with empty liposomes. The middle and deep layers of the hyaline articular cartilage were characterized by highly increased COMP expression in liposomal clodronate treated AIA joints compared to controls. In contrast to cartilage, synovial COMP expression was slightly decreased as a result of liposomal clodronate treatment.

CONCLUSION

Low-dose, non-cytotoxic liposomal clodronate exerts a dichotomous effect on synovial membrane and articular cartilage COMP in the AIA model. COMP is a useful inflammation marker in the synovial tissue, but it also contributes to the structural integrity of the hyaline articular cartilage forming bridges between type II and IX collagens. Enhancement of COMP in clodronate treated AIA cartilage suggests a chondroprotective and anti-inflammatory effect in the inflammatorily damaged and mechanically strained cartilage.

Involvement of TNF-Like Weak Inducer of Apoptosis in the Pathogenesis of Collagen-Induced Arthritis

TNF-like weak inducer of apoptosis (TWEAK) is a type II membrane protein belonging to the TNF family that regulates apoptotic cell death, cellular proliferation, angiogenesis, and inflammation. However, the role of TWEAK in the pathogenesis of rheumatoid arthritis (RA) remains unclear. In this study, we have investigated the effect of neutralizing anti-TWEAK mAb on the development of collagen-induced arthritis (CIA), a well-established murine model of RA. Administration of anti-TWEAK mAb significantly ameliorated paw swelling, synovial hyperplasia, and infiltration of inflammatory cells. The levels of proinflammatory chemokines such as MCP-1 and MIP-2 in serum and knee joints were reduced by this treatment. Consistently, recombinant TWEAK enhanced the proliferation of MCP-1 and MIP-2 production by synovial cells from CIA mice in vitro. Histological examination also revealed that the treatment with anti-TWEAK mAb suppressed the development of small vessels in synovial tissues. These results indicated anti-inflammatory and antiangiogenic effects of the TWEAK blockade in CIA, which may be also beneficial for the treatment of RA.

Lipidation and glycosylation of a T cell antigen receptor (TCR) transmembrane hydrophobic peptide dramatically enhances in vitro and in vivo function

A T cell antigen receptor (TCR) transmembrane sequence derived peptide (CP) has been shown to inhibit T cell activation both in vitro and in vivo at the membrane level of the receptor signal transduction. To examine the effect of sugar or lipid conjugations on CP function, we linked CP to 1-aminoglucosesuccinate (GS), N-myristate (MYR), mono-di-tripalmitate (LP1, LP2, or LP3), and a lipoamino acid (LA) and examined the effects of these compounds on T cell activation in vitro and by using a rat model of adjuvant-induced arthritis, in vivo. In vitro, antigen presentation results demonstrated that lipid conjugation enhanced CP's ability to lower IL-2 production from 56.99%+/-15.69 S.D. observed with CP, to 12.08%+/-3.34 S.D. observed with LA. The sugar conjugate GS resulted in only a mild loss of in vitro activity compared to CP (82.95%+/-14.96 S.D.). In vivo, lipid conjugation retarded the progression of adjuvant-induced arthritis by approximately 50%, whereas the sugar conjugated CP, GS, almost completely inhibited the progression of arthritis. This study demonstrates that hydrophobic peptide activity is markedly enhanced in vitro and in vivo by conjugation to lipids or sugars. This may have practical applications in drug delivery and bioavailability of hydrophobic peptides.

Essential role of neutrophils in anti-type II collagen antibody and lipopolysaccharide-induced arthritis

In mice arthritis model induced by anti-type II collagen (CII) antibodies and lipopolysaccharide (LPS), most of cells that infiltrated into the joint space were neutrophils. To investigate the role of neutrophils in the pathogenesis of arthritis, we depleted the neutrophils in vivo by injection of the antibody against Gr-1 expressed mainly on neutrophils. The neutrophil depletion completely inhibited the arthritis development. Furthermore, neutrophil depletion in mice that had already developed arthritis ameliorated the disease. These results showed that neutrophils are indispensable not only for the development, but also for the maintenance of arthritis. Next, we tried to develop arthritis in C5-deficient mice to investigate the involvement of C5a, one of chemotactic factors for neutrophils. C5-deficient mice showed significant reduction in arthritis development in comparison with wild type mice. Injection of pertussis toxin (Ptx) into the mice, which inhibits the signals from the inhibitory G-protein coupled-receptors including the C5a receptor, suppressed the development of arthritis. Furthermore, Ptx also ameliorated the arthritis when injected into mice that had already developed the disease. These results suggest the important role of chemotactic factors involving C5a and inhibitory G-protein (Gi)-coupled receptors not only in the development, but also in the maintenance of arthritis.