Tranilast Suppresses the Disease Development of the Adjuvant- and Streptococcal Cell Wall-Induced Arthritis in Rats

Role of NLRP3 Inflammasome in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by multi-articular, symmetrical and invasive arthritis resulting from immune system abnormalities involving T and B lymphocytes. Although significant progress has been made in the understanding of RA pathogenesis, the underlying mechanisms are not fully understood. Recent studies suggest that NLRP3 inflammasome, a regulator of inflammation, might play an important role in the development of RA. There have been increasing clinical and pre-clinical evidence showing the treatment of NLRP3/IL-1β in inflammatory diseases. To provide a foundation for the development of therapeutic strategies, we will briefly summarize the roles of NLRP3 inflammasome in RA and explore its potential clinical treatment.

Understanding the Role of Inflammasomes in Rheumatoid Arthritis

Inflammasomes are the molecular pathways that activate upon conditions of infection or stress and trigger the activation and maturation of inflammatory cytokines. Immune reactions in conjugation with inflammatory processes play a pivotal role in developing innumerable diseases. An over reactive immune system fabricates many allergic and hypersensitive reactions in response to autoantibodies activated against modified self-epitopes and similar molecules. Rheumatoid arthritis (RA) is a complex autoimmune inflammatory disorder commencing with inflammation in small joints like hands, knees, and wrist eventually entrapping larger joints such as spine. The formation of autoantibodies called rheumatoid factor (RF) and citrullinated proteins against immunoglobulin G symbolizes autoimmune nature of the disease. The presence of autoantibodies embarks principal diagnostic hallmark of the disease. With the advancement of technology, the therapeutic approach is also advancing. A new era of molecules, namely inflammasomes, are activated upon infection or in response to stress and trigger the activation of various proinflammatory cytokines such interleukins which engage in the defense mechanism of the innate immunity. Robust linking among the activity of dysregulated inflammasomes and the heritable acquired inflammatory diseases and disorders emphasizes the significance of this pathway in altering the immune responses. The current review highlights the functioning of inflammasomes and their possible role in disease dysregulation.

Aleurites moluccanus and its main active constituent, the flavonoid 2″-O-rhamnosylswertisin, in experimental model of rheumatoid arthritis

ETHNOPHARMMACOLOGICAL RELEVANCE

Aleurites moluccana is used in folk medicine to treat pain, fever, asthma, hepatitis, gastric ulcer and inflammatory process in general, and the nut oil had been topically applied to treat arthritis and other joint pain, however the seeds are classified as toxic for oral use.

AIM

Faced with the need for new alternative to treat the symptoms and modify rheumatoid arthritis (RA) the aim of this work was to evaluate the effects of A. moluccanus' leaves dried extract in rats and mice submitted to complete Freund adjuvant (CFA)-induced RA.

MATERIAL AND METHODS

Wistar Rats and Swiss mice were submitted to CFA-induced RA in the right hindpaw. They received A. moluccanus extract (orally; p.o.), dexamethasone (subcutaneously), 2″-O-rhamnosylswertisin (p.o.) or vehicle (p.o.), from the 14th day after the CFA injection for up to 8 days. The mechanical hypersensitivity was evaluated using the von Frey filaments and the paw-oedema was measured using a plethysmometer. The rats' injected hindpaw was used to perform the histological analysis.

RESULTS

A. moluccanus was able to significantly reduce the mechanical hypersensitivity in both ipsi- and contralateral hindpaws of mice injected with CFA, in a dose dependent manner. Furthermore, the paw-oedema was progressively reduced by A. moluccanus. Similar results were obtained for the positive-control drug dexamethasone and the isolated compound 2″-O-rhamnosylswertisin. Besides the effects mentioned above, the extract was also effective to repair the joint damage in CFA-induced RA rats, including reduction of fibrosis, cartilage degradation and bone erosion scores.

CONCLUSION

These results together with the literature data reinforce the anti-hypersensitivity and anti-inflammatory activity of A. moluccanus extract. Part of the observed effects is due to the presence of the compound 2″-O-rhamnosylswertisin. The fact that the extract acted as a disease modifier point this herbal product as a promisor and safe tool to treat RA and other associated chronic diseases.

Anti-arthritic potential of marine macroalgae Turbinaria ornata in Complete Freund's Adjuvant induced rats

T. ornata a macroalgae rich in bioactive molecules possess various biological activities. Herein, the aim of the study is to evaluate the aqueous extract and the sulphated polysaccharide isolated from T. ornata for its anti-arthritic potential in Complete Freund's Adjuvant (CFA) induced arthritis in rats. Anti-arthritic potential of aqueous T. ornata (ATO) and T. ornata sulphated polysaccharide (TSP) was evidenced by the significant reduction in paw volume and arthritic score. Inflammatory and antioxidant markers were found to be restored in the drug treated groups which was found to be in line with dexamethasone a standard anti-inflammatory drug. The histopathological and radiological examination adds on the support to the above findings confirming the anti-arthritic potential of ATO and TSP. It is interesting to note that the sulphated polysaccharide inhibits inflammation and bone damage at very low dose itself. Hence, TSP could be considered as a better candidate in the management of chronic inflammatory diseases like rheumatoid arthritis.

Tranilast: a review of its therapeutic applications

Tranilast (N-[3',4'-dimethoxycinnamoyl]-anthranilic acid) is an analog of a tryptophan metabolite. Initially, tranilast was identified as an anti-allergic agent, and used in the treatment of inflammatory diseases, such as bronchial asthma, atypical dermatitis, allergic conjunctivitis, keloids and hypertrophic scars. Subsequently, the results showed that it could be also effective in the management of a wide range of conditions. The beneficial effects of tranilast have also been seen in a variety of disease states, such as fibrosis, proliferative disorders, cancer, cardiovascular problems, autoimmune disorders, ocular diseases, diabetes and renal diseases. Moreover, several trials have shown that it has very low adverse effects and it is generally well tolerated by patients. In this review, we have attempted to accurately summarize previously published studies relating to the use of tranilast for a range of disorders and discuss the drug's possible mode of action. The major mode of the drug's efficacy appears to be the suppression of the expression and/or action of the TGF-β pathway, but the drug affects other factors as well. The findings presented in this review demonstrate the potential of tranilast for the control of a vast array of pathological situations, furthermore, it is a prescribed drug without severe side effects.

Exploitation of the IDO Pathway in the Therapy of Rheumatoid Arthritis

Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting step along the kynurenine pathway and is thought to play a key role in immune homeostasis through depletion of tryptophan and accumulation of kynurenines. In this review we summarize recent research into the possibility of harnessing the IDO pathway for the therapy of rheumatoid arthritis. Inhibition of IDO activity, or knockout of the gene encoding IDO, was shown to cause an increase in the severity of collagen-induced arthritis, an animal model of rheumatoid arthritis. The increased severity of disease was associated with elevated numbers of pathogenic Th1 and Th17 cells in the joints and draining lymph nodes. In another study, analysis of the kinetics of expression of downstream kynurenine pathway enzymes during the course of arthritis revealed a potential role for tryptophan metabolites in resolution of arthritis. Furthermore, the therapeutic administration of L-kynurenine or [3,4-dimethoxycinnamonyl]-anthranilic acid (a synthetic derivative of 3-hydroxy-anthranilic acid) significantly reduced both clinical and histological progression of experimental arthritis. These findings raise the possibility of exploiting the IDO pathway for the therapy of autoimmune disease.

Advances in research on animal models of rheumatoid arthritis

At present, rheumatoid arthritis (RA) is considered a type of autoimmune disease. Its pathology is not certain, and effective drugs with less toxicity have not been established. The establishment and application of animal models are effective methods for RA research, especially using animal models similar to humans. Arthritis is more heterogeneous, and this is an important starting point when discussing animal models for arthritis. Animal models are instrumental in understanding the etiology and pathogenetic mechanisms of RA. Appropriate animal models should be selected according to experiments because they have different traits. Various methods have been applied to induce arthritis in animal experimental models, which have provided important insights into the etiopathogenetic mechanisms of human RA. This review was written to give a broad introduction of the current stage of RA model and hope to offer beneficial help for RA-related research.

Tissue-engineered cartilage of porcine and human origin as in vitro test system in arthritis research

The increasing prevalence of cartilage destruction during arthritis has entailed an intensified amount for in vitro cartilage models to analyze pathophysiological processes and to screen for antirheumatic drugs. Tissue engineering offers the opportunity to establish highly organized 3D cell cultures facilitating the formation of in vitro models that reflect the human situation. We report the comparison of porcine chondrocyte pellet and alginate bead cultures as model systems for human cartilage and the further development into a human system that was applied in an arthritis model. In porcine pellet and alginate cultures, formation of cartilage matrix similar to human matrix was verified by histology and PCR. As alginate beads could be cultivated batch-wise in one well of a multiwell plate, we further developed this setting into a human system. In contrast, each pellet had to be cultivated individually in one well of a multiwell plate, which is time consuming. Following stimulation of human chondrocyte alginate cultures with conditioned media from human synovial fibroblasts derived from arthritis patients, microarray analysis verified the induction of genes related to cartilage destruction (like MMP10, -12) and inflammation (like IL6, -8 and chemokines). Several genes are coding for proteins that are members of inflammatory and catabolic pathways. Belonging to the most affected pathways, we identified the focal adhesion, cytokine-cytokine receptor interaction, ECM-receptor signalling, Jak-STAT signalling, and toll-like receptor signalling pathways, all relevant in arthritis. Therefore, we demonstrate that engineered cartilage of porcine and human origin represents a powerful in vitro model for cartilage in vivo.

The anti-allergic compound tranilast attenuates inflammation and inhibits bone destruction in collagen-induced arthritis in mice

BACKGROUND AND PURPOSE

Recent findings suggest the importance of mast cells in the pathogenesis of rheumatoid arthritis and their potential as a therapeutic target. Tranilast is an anti-allergic compound with a potent membrane-stabilizing effect on mast cells and a wide range of anti-inflammatory effects, thus may be advantageous in the treatment of arthritis. Here, we have evaluated the effects of tranilast on the progression of collagen-induced arthritis in mice.

EXPERIMENTAL APPROACH

Tranilast (400 mg.kg(-1).day(-1)) was orally administered for 8 weeks to mice with established collagen-induced arthritis. Arthritis was assessed by clinical signs and X-ray scores. In paw tissue, the numbers of mast cells and osteoclasts were measured by histological analysis, and several inflammatory factors were assessed by RT-PCR and Western blot analysis.*

KEY RESULTS

TNF-alpha-positive mast cells were present extensively throughout the inflamed synovium of vehicle-treated arthritic mice, with some mast cells in close proximity to osteoclasts in areas of marked bone and cartilage destruction. Tranilast significantly reduced clinical and X-ray scores of arthritis and decreased numbers of TNF-alpha-positive mast cells and mRNA levels of TNF-alpha, chymase (mouse mast cell protease 4), tryptase (mouse mast cell protease 6), stem cell factor, interleukin-6, cathepsin-K, receptor activator of nuclear factor-kappaB, and of receptor activator of nuclear factor-kappaB-ligand, but increased interleukin-10 mRNA level in paws of arthritic mice. Osteoclast numbers were decreased by treatment with tranilast.

CONCLUSIONS AND IMPLICATIONS

Tranilast possesses significant anti-rheumatic efficacy and, probably, this therapeutic effect is partly mediated by inhibition of mast cell activation and osteoclastogenesis.