Combination therapy with dexamethasone and osteoprotegerin protects against arthritis-induced bone alterations in antigen-induced arthritis of the rat

Mechanisms of Systemic Osteoporosis in Rheumatoid Arthritis

Rheumatoid arthritis (RA), an autoimmune disease, is characterized by the presence of symmetric polyarthritis predominantly of the small joints that leads to severe cartilage and bone destruction. Based on animal and human data, the pathophysiology of osteoporosis, a frequent comorbidity in conjunction with RA, was delineated. Autoimmune inflammatory processes, which lead to a systemic upregulation of inflammatory and osteoclastogenic cytokines, the production of autoantibodies, and Th cell senescence with a presumed disability to control the systemic immune system's and osteoclastogenic status, may play important roles in the pathophysiology of osteoporosis in RA. Consequently, osteoclast activity increases, osteoblast function decreases and bone metabolic and mechanical properties deteriorate. Although a number of disease-modifying drugs to treat joint inflammation are available, data on the ability of these drugs to prevent fragility fractures are limited. Thus, specific treatment of osteoporosis should be considered in patients with RA and an associated increased risk of fragility fractures.

Dexamethasone: chondroprotective corticosteroid or catabolic killer?

While glucocorticoids have been used for over 50 years to treat rheumatoid and osteoarthritis pain, the prescription of glucocorticoids remains controversial because of potentially harmful side effects at the molecular, cellular and tissue levels. One member of the glucocorticoid family, dexamethasone (DEX) has recently been demonstrated to rescue cartilage matrix loss and chondrocyte viability in animal studies and cartilage explant models of tissue injury and post-traumatic osteoarthritis, suggesting the possibility of DEX as a disease-modifying drug if used appropriately. However, the literature on the effects of DEX on cartilage reveals conflicting results on the drug's safety, depending on the dose and duration of DEX exposure as well as the model system used. Overall, DEX has been shown to protect against arthritis-related changes in cartilage structure and function, including matrix loss, inflammation and cartilage viability. These beneficial effects are not always observed in model systems using initially healthy cartilage or isolated chondrocytes, where many studies have reported significant increases in chondrocyte apoptosis. It is crucially important to understand under what conditions DEX may be beneficial or harmful to cartilage and other joint tissues and to determine potential for safe use of this glucocorticoid in the clinic as a disease-modifying drug.

Therapeutic effect of farnesylthiosalicylic acid on adjuvant-induced arthritis through suppressed release of inflammatory cytokines

Rheumatoid arthritis (RA) is an autoimmune disease characterized by pronounced inflammation and leucocyte infiltration in affected joints. Despite significant therapeutic advances, a new targeted approach is needed. Our objective in this work was to investigate the anti-inflammatory effects of the Ras inhibitor farnesylthiosalicylic acid (FTS) on adjuvant-induced arthritis (AIA) in rats, an experimental model for RA. Following AIA induction in Lewis rats by intradermal injection of heat-killed Mycobacterium tuberculosis, rats were treated with either FTS or dexamethasone and assessed daily for paw swelling. Joints were imaged by magnetic resonance imaging and computerized tomography and analysed histologically. The anti-inflammatory effect of FTS was assessed by serum assay of multiple cytokines. After adjuvant injection rats demonstrated paw swelling, leucocyte infiltration, cytokine secretion and activation of Ras-effector pathways. Upon FTS treatment these changes reverted almost to normal. Histopathological analysis revealed that the synovial hyperplasia and leucocyte infiltration observed in the arthritic rats were alleviated by FTS. Periarticular bony erosions were averted. Efficacy of FTS treatment was also demonstrated by inhibition of CD4(+) and CD8(+) T cell proliferation and of interferon (IFN)-γ, tumour necrosis factor (TNF)-α, interleukin (IL)-6 and IL-17 release. The Ras effectors PI3K, protein kinase B (AKT), p38, and extracellular-regulated kinase (ERK) were significantly attenuated and forkhead box protein 3 (FoxP3) transcription factor, a marker of regulatory T cells, was significantly increased. Thus, FTS possesses significant anti-inflammatory and anti-arthritic properties and accordingly shows promise as a potential therapeutic agent for RA. Its effects are apparently mediated, at least in part, by a decrease in proinflammatory cytokines.

Melatonin treatment entrains the rest-activity circadian rhythm in rats with chronic inflammation

We assessed the therapeutic effect of exogenous melatonin (MEL), dexamethasone (DEXA), and a combination of both on nociceptive response induced by chronic inflammation and on the rest-activity circadian rhythm in rats. A total of 64 animals were randomly divided into eight groups of eight rats each: one control group and seven groups with complete Freund's adjuvant-inflamed animals (CFA; injection into the footpad). One of the CFA-inflamed groups did not receive any treatment; the other six were treated with melatonin (MEL), dexamethasone (DEXA), melatonin plus dexamethasone (MELDEXA), and their respective vehicles. Fifteen days after CFA injection, animals were treated with intraperitoneal injection of MEL (50 mg/kg) or its vehicle (8% ethanol in saline), DEXA (0.25 mg/kg) or its vehicle (saline), and MEL plus DEXA or their vehicles, for 8 days. The von Frey test was performed 24 h after the last administration of each treatment regimen. Hind paw thickness was measured using a pachymeter during the treatment days. The degree of swelling and histological findings were analyzed. All treated groups significantly reduced the severity of inflammation when compared with their vehicles (repeated-measures analysis of variance [ANOVA], p < 0.05 for all analyses). Inflamed animals treated with dexamethasone alone or associated with melatonin showed marked inhibition of histological findings. On the other hand, the group treated with melatonin remained with moderate inflammation. The CFA group showed a decrease in the mean rest-activity circadian rhythm, determined by the number of touch-detections per hour during water intake in comparison with the control group; only the group treated with melatonin showed a synchronized rest-activity rhythm. At the end of treatment, a significant increase was observed in hind paw withdrawal threshold on the von Frey test in the treated groups (one-way ANOVA, p < 0.05 for all). Our findings showed that melatonin (50 mg/kg) has strong chronobiotic and antinociceptive effects, but only mild anti-inflammatory effects. This evidence supports the hypothesis that melatonin can induce phase advance and circadian rhythm synchronization in rats with chronic inflammation.

Spinal cord brain-derived neurotrophic factor levels increase after dexamethasone treatment in male rats with chronic inflammation

Dexamethasone is widely used in the therapy of chronic inflammatory diseases for its pain-modulating effects. The objective of this study was to evaluate the effect of dexamethasone on nociception and local inflammation, and the levels of brain-derived neurotrophic factor (BDNF) in the spinal cord in male rats with chronic inflammation induced by complete Freund's adjuvant (CFA). Rats were randomly divided into a control group (not manipulated) and 2 CFA-induced chronic inflammation groups (in the 15th post-CFA injection): 1 injected with vehicle (saline solution) and 1 received dexamethasone (0.25 mg/kg) for 8 days. The hot-plate and electronic von Frey tests were performed 24 h after the end of treatment. BDNF spinal cord levels were determined by enzyme-linked immunosorbent assay (ELISA). The level of inflammation in the tibiotarsal joint (the ankle region) was evaluated histologically at the end of treatment. Dexamethasone produced significantly increased latency in the hot-plate test (one-way ANOVA, p < 0.05) and withdrawal threshold in the electronic von Frey test (p < 0.005). The dexamethasone group showed increased spinal cord BDNF levels compared to the other groups (one-way ANOVA p, < 0.05). Histological analysis showed a local inflammatory response only in animals treated with vehicle, which demonstrated that the dexamethasone treatment decreased the inflammatory process. Our findings corroborate the antinociceptive and anti-inflammatory properties of dexamethasone. In addition, we showed that the dexamethasone treatment increased BDNF levels in the spinal cord; its pain- modulating effects can be attributed to this effect.

Skeletal and extraskeletal actions of denosumab

Osteoclasts and osteoblasts define skeletal mass, structure and strength through their respective actions in resorbing and forming bone. This remodeling process is orchestrated by the actions of hormones and growth factors, which regulate a cytokine system comprising the receptor activator of nuclear factor κB ligand (RANKL), its receptor RANK and the soluble decoy receptor osteoprotegerin (OPG). Bone resorption depends on RANKL, which determines osteoclast formation, activity and survival. Importantly, cells of the osteoblastic lineage mainly provide RANKL and therefore, are central in the regulation of osteoclast functions. Catabolic effects of RANKL are inhibited by OPG, a TNF receptor family member that binds RANKL, thereby preventing the activation of its receptor RANK, which is expressed by osteoclast precursors. Because this cytokine network is pivotal for the regulation of bone mass in health and diseases, including osteoporosis, rheumatoid arthritis and malignant bone conditions, it has been successfully used for the generation of a targeted therapy to block osteoclast actions. The clinical approval of denosumab, a fully monoclonal antibody against RANKL, provides a novel option to treat bone diseases with a potent, targeted and reversible inhibitor of bone resorption. Although RANKL is also expressed by endothelial cells, T lymphocytes, synovial fibroblasts and various tumor cells, no meaningful clinical extraskeletal effects have been reported after administration of denosumab. This article summarizes the molecular and cellular basis of the RANKL/RANK/OPG system and presents preclinical and clinical studies on the skeletal actions of denosumab.