Expression and functional role of adenosine receptors in regulating inflammatory responses in human synoviocytes

Electroacupuncture Inhibits Cartilage Degeneration in a Rat Knee Osteoarthritis (KOA) Model by Suppressing ADAMTS5 Expression

Background Knee osteoarthritis (KOA) is characterized by cartilage degradation, osteophyte formation, and synovitis. Cartilage degradation in KOA begins with the loss of aggrecan, primarily due to A Disintegrin and Metalloproteinase with Thrombospondin Motif 5 (ADAMTS5), which is produced by chondrocytes and synovial cells and a key target for therapeutic intervention. Current treatments for KOA primarily focus on pain relief, as disease-modifying osteoarthritis drugs (DMOADs) remain unavailable. Electroacupuncture (EA), applying electrical stimulation to acupoints, has been investigated for its potential to alleviate KOA symptoms; however, the specific effects of different acupoint combinations remain unclear. This study investigates the effect of EA on pain and cartilage degeneration in a KOA rat model by examining ADAMTS5 expression in synovial tissue. Materials and methods Male Wistar rats were divided into five groups: control, sham-operated, KOA model, KOA treated with EA at ST36 (Zusanli)-LR8 (Ququan) (KOA+LR8), and KOA treated at ST36-Ex-LE2 (Heding) (KOA+Ex-LE2). The DMM (destabilization of the medial meniscus) procedure induced KOA, and EA was applied thrice weekly for four weeks. The rotarod test was used to assess motor coordination, and samples were collected for immunofluorescence, Western blot, and histological analysis. Pain was assessed via c-fos expression in the spinal cord, while Safranin O-Fast Green staining was used to evaluate cartilage degeneration via the Osteoarthritis Research Society International (OARSI) scoring system. Results The KOA group post-surgery showed reduced motor coordination, while EA at both ST36-LR8 and ST36-Ex-LE2 enhanced performance (day 28: control: 28.8 ± 0.6, sham: 28.4 ± 3.7, KOA: 19.7 ± 0.9, KOA+LR8: 24.8 ± 1.5, KOA+Ex-LE2: 26.9 ± 1.2). Expression of c-fos, elevated in the KOA group, was significantly suppressed by EA (control: 7.6 ± 0.9, sham: 13.6 ± 2.8, KOA: 24.5 ± 2.1, KOA+LR8: 12.8 ± 0.9, KOA+Ex-LE2: 17.0 ± 1.2). Histologically, KOA rats showed severe cartilage degradation and osteophyte formation, while EA at ST36-Ex-LE2 significantly reduced these changes (control: 0.2 ± 0.1, sham: 0.4 ± 0.2, KOA: 1.8 ± 0.4, KOA+LR8: 1.0 ± 0.2, KOA+Ex-LE2: 0.5 ± 0.2). The ST36-LR8 group also showed improvements, although less pronounced than the ST36-Ex-LE2 group. Western blotting revealed that DMM-induced ADAMTS5 expression was significantly inhibited by EA at ST36-Ex-LE2 but not at ST36-LR8 (control: 1.0 ± 0, sham: 1.2 ± 0.4, KOA: 3.0 ± 0.3, KOA+LR8: 2.1 ± 0.3, KOA+Ex-LE2: 1.4 ± 0.4). Conclusion EA at ST36-Ex-LE2 showed a remarkable protective effect on articular cartilage by inhibiting ADAMTS5 expression from synovium, suggesting that it can break the vicious cycle of synovitis and cartilage destruction. In contrast, EA at ST36-LR8 had a moderate effect on cartilage degeneration and ADAMTS5 expression. The difference in efficacy may be due to the anatomical differences between acupoints. ST36-Ex-LE2 coincides with an area rich in synovial fibroblasts and mast cells involved in inflammation and pain. This highlights the importance of acupoint selection to maximize the therapeutic effect of EA. The specificity of this acupoint combination provides a potential strategy for managing KOA and slowing the progression of the disease. Further studies are needed to elucidate the detailed mechanisms behind the effects of EA and explore its potential as an alternative or complementary treatment for KOA.

Temporal Dynamics of Purinergic Receptor Expression in the Lungs of Marek's Disease (MD) Virus-Infected Chickens Resistant or Susceptible to MD

Marek's disease virus (MDV) is an economic concern for the poultry industry due to its poorly understood pathophysiology. Purinergic receptors (PRs) are potential therapeutic targets for viral infections, including herpesviruses, prompting our investigation into their role in MDV pathogenesis. The current study is part of an experimental series analyzing the expression of PRs during MDV infection. To address the early or short-acting P2 PR responses during natural MDV infection, we performed an "exposure" experiment where age-matched chickens were exposed to experimentally infected shedders to initiate natural infection. In addition, select non-PR regulatory gene responses were measured. Two groups of naïve contact chickens (n = 5/breed/time point) from MD-resistant (White Leghorns: WL) and -susceptible (Pure Columbian) chicken lines were housed separately with experimentally infected PC (×PC) and WL (×WL) chickens for 6 or 24 h. Whole lung lavage cells (WLLC) were collected, RNA was extracted, and RT-qPCR assays were used to measure specific PR responses. In addition, other potentially important markers in pathophysiology were measured. Our study revealed that WL chickens exhibited higher P1 PR expression during natural infection. WL chickens also showed higher expression of P1A3 and P2X3 at 6 and 24 h when exposed to PC-infected chickens. P2X5 and P2Y1 showed higher expression at 6 h, while P2Y5 showed higher expression at 6 and 24 h; regardless of the chicken line, PC chickens exhibited higher expression of P2X2, P2Y8, P2Y10, P2Y13, and P2Y14 when exposed to either group of infected chickens. In addition, MDV infection altered the expression of DDX5 in both WL and PC groups exposed to PC-infected birds only. However, irrespective of the source of exposure, BCL2 and ANGPTL4 showed higher expression in both WL and PC. The expression of STAT1A and STAT5A was influenced by time and breed, with major changes observed in STAT5A. CAT and SOD1 expression significantly increased in both WL and PC birds, regardless of the source of infection. GPX1 and GPX2 expression also increased in both WL and PC, although overall lower expression was observed in PC chickens at 24 h compared to 6 h. Our data suggest systemic changes in the host during early infection, indicated by the altered expression of PRs, DDX5, BCL2, ANGPTL4, and other regulatory genes during early MDV infection. The relative expression of these responses in PC and WL chickens suggests they may play a key role in their response to natural MDV infection in the lungs and long-term pathogenesis and survival.

Adenosine A3 Receptor: From Molecular Signaling to Therapeutic Strategies for Heart Diseases

Cardiovascular diseases (CVDs), particularly heart failure, are major contributors to early mortality globally. Heart failure poses a significant public health problem, with persistently poor long-term outcomes and an overall unsatisfactory prognosis for patients. Conventionally, treatments for heart failure have focused on lowering blood pressure; however, the development of more potent therapies targeting hemodynamic parameters presents challenges, including tolerability and safety risks, which could potentially restrict their clinical effectiveness. Adenosine has emerged as a key mediator in CVDs, acting as a retaliatory metabolite produced during cellular stress via ATP metabolism, and works as a signaling molecule regulating various physiological processes. Adenosine functions by interacting with different adenosine receptor (AR) subtypes expressed in cardiac cells, including A1AR, A2AAR, A2BAR, and A3AR. In addition to A1AR, A3AR has a multifaceted role in the cardiovascular system, since its activation contributes to reducing the damage to the heart in various pathological states, particularly ischemic heart disease, heart failure, and hypertension, although its role is not as well documented compared to other AR subtypes. Research on A3AR signaling has focused on identifying the intricate molecular mechanisms involved in CVDs through various pathways, including Gi or Gq protein-dependent signaling, ATP-sensitive potassium channels, MAPKs, and G protein-independent signaling. Several A3AR-specific agonists, such as piclidenoson and namodenoson, exert cardioprotective impacts during ischemia in the diverse animal models of heart disease. Thus, modulating A3ARs serves as a potential therapeutic approach, fueling considerable interest in developing compounds that target A3ARs as potential treatments for heart diseases.

Pharmacology of Adenosine Receptors: Recent Advancements

Adenosine receptors (ARs) are widely acknowledged pharmacological targets yet are still underutilized in clinical practice. Their ubiquitous distribution in almost all cells and tissues of the body makes them, on the one hand, excellent candidates for numerous diseases, and on the other hand, intrinsically challenging to exploit selectively and in a site-specific manner. This review endeavors to comprehensively depict the substantial advancements witnessed in recent years concerning the development of drugs that modulate ARs. Through preclinical and clinical research, it has become evident that the modulation of ARs holds promise for the treatment of numerous diseases, including central nervous system disorders, cardiovascular and metabolic conditions, inflammatory and autoimmune diseases, and cancer. The latest studies discussed herein shed light on novel mechanisms through which ARs exert control over pathophysiological states. They also introduce new ligands and innovative strategies for receptor activation, presenting compelling evidence of efficacy along with the implicated signaling pathways. Collectively, these emerging insights underscore a promising trajectory toward harnessing the therapeutic potential of these multifaceted targets.

Role of the Sympathetic Nervous System in Mild Chronic Inflammatory Diseases: Focus on Osteoarthritis

The sympathetic nervous system (SNS) is a major regulatory mediator connecting the brain and the immune system that influences accordingly inflammatory processes within the entire body. In the periphery, the SNS exerts its effects mainly via its neurotransmitters norepinephrine (NE) and epinephrine (E), which are released by peripheral nerve endings in lymphatic organs and other tissues. Depending on their concentration, NE and E bind to specific α- and β-adrenergic receptor subtypes and can cause both pro- and anti-inflammatory cellular responses. The co-transmitter neuropeptide Y, adenosine triphosphate, or its metabolite adenosine are also mediators of the SNS. Local pro-inflammatory processes due to injury or pathogens lead to an activation of the SNS, which in turn induces several immunoregulatory mechanisms with either pro- or anti-inflammatory effects depending on neurotransmitter concentration or pathological context. In chronic inflammatory diseases, the activity of the SNS is persistently elevated and can trigger detrimental pathological processes. Recently, the sympathetic contribution to mild chronic inflammatory diseases like osteoarthritis (OA) has attracted growing interest. OA is a whole-joint disease and is characterized by mild chronic inflammation in the joint. In this narrative article, we summarize the underlying mechanisms behind the sympathetic influence on inflammation during OA pathogenesis. In addition, OA comorbidities also accompanied by mild chronic inflammation, such as hypertension, obesity, diabetes, and depression, will be reviewed. Finally, the potential of SNS-based therapeutic options for the treatment of OA will be discussed.

Purinergic signaling during Marek's disease in chickens

Purinergic receptors (PRs) have been reported as potential therapeutic targets for many viral infections including herpesviruses, which urges the investigation into their role in Marek's disease (MD), a herpesvirus induced cancer in chickens that is an important pathogen for the poultry industry. MD is caused by MD virus (MDV) that has a similar viral life cycle as human varicella zoster virus in that it is shed from infected epithelial skin cells and enters the host through the respiratory route. In this report, PR responses during natural MDV infection and disease progression was examined in MD-resistant white Leghorns (WL) and MD-susceptible Pure Columbian (PC) chickens during natural infection. Whole lung lavage cells (WLLC) and liver tissue samples were collected from chickens infected but showing no clinical signs of MD (Infected) or presenting with clinical disease (Diseased). RNA was extracted followed by RT-qPCR analysis with gene specific primers against members of the P1, P2X, and P2Y PR families. Differential expression (p < 0.05) was observed in breed and disease conditions. Some PRs showed tissue specific expression (P1A1, P2X1, and P2X6 in WLLC) whereas others responded to MDV infection only in MD-susceptible (PC) chickens (P1A2A, P2X1, P2X5, P2X7). P2Y PRs had differential expression in both chicken lines in response to MDV infection and MD progression. This study is the first to our knowledge to examine PR responses during MDV infection and disease progression. These results suggest PR signaling may an important area of research for MDV replication and MD.

Pulsed Electromagnetic Field Enhances Healing of a Meniscal Tear and Mitigates Posttraumatic Osteoarthritis in a Rat Model

BACKGROUND

Meniscal tears in the avascular region are thought to rarely heal and are a considerable challenge to treat. Although the therapeutic effects of a pulsed electromagnetic field (PEMF) have been extensively studied in a variety of orthopaedic disorders, the effect of a PEMF on meniscal healing has not been reported.

HYPOTHESIS

PEMF treatment would promote meniscal healing and prevent osteoarthritis progression.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 72 twelve-week-old male Sprague-Dawley rats with full-thickness longitudinal medial meniscal tears in the avascular region were divided into 3 groups: control (G_con), treatment with a classic signal PEMF (G_classic), and treatment with a high-slew rate signal PEMF (G_HSR). Macroscopic observation and histological analysis of the meniscus and articular cartilage were performed to evaluate the meniscal healing and progression of osteoarthritis. The synovium was harvested for histological and immunofluorescent analysis to evaluate the intra-articular inflammation. Meniscal healing, articular cartilage degeneration, and synovitis were quantitatively evaluated according to their scoring systems.

RESULTS

Dramatic degenerative changes of the meniscus and articular cartilage were noticed during gross observation and histological evaluation in G_con at 8 weeks. However, the menisci in the 2 treatment groups were restored to normal morphology, with a smooth surface and shiny white color. Particularly, the HSR signal remarkably enhanced the fibrochondrogenesis and accelerated the remodeling process of the regenerated tissue. The meniscal healing scores of the PEMF treatment groups were significantly higher than those in G_con at 8 weeks. Specifically, the HSR signal showed a significantly higher meniscal repair score than did the classic signal at week 8 (P < .01). Additionally, the HSR signal significantly downregulated the secretion levels of interleukin 1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in the meniscus and synovium as compared with the control group. When compared with the 2 treatment groups, G_con had significantly higher degeneration scores (G_con vs G_classic, P < .0001; G_con vs G_HSR, P < .0001). The HSR signal also exhibited significantly lower synovitis scores compared with the other two groups (G_con vs G_classic, P < .0001; G_classic vs G_HSR, P = .0002).

CONCLUSION

A PEMF promoted the healing of meniscal tears in the avascular region and restored the injured meniscus to its structural integrity in a rat model. As compared with the classic signal, the HSR signal showed increased capability to promote fibrocartilaginous tissue formation and modulate the inflammatory environment, therefore protecting the knee joint from posttraumatic osteoarthritis development.

CLINICAL RELEVANCE

Adjuvant PEMF therapy may offer a new approach for the treatment of meniscal tears attributed to the enhanced meniscal repair and ameliorated osteoarthritis progression.

Activation of adenosine A3 receptor attenuates progression of osteoarthritis through inhibiting the NLRP3/caspase-1/GSDMD induced signalling

The specific adenosine A3 receptor (A3AR) agonist (CF101) has potential for inflammation and pain in various disease, such as arthritis, cancer and neuropathic pain, while the role of A3AR in post-traumatic OA and the underlying mechanism is largely unknown. CF101 was orally administrated in OA rats induced by anterior cruciate ligament transection (ACLT) surgery, and the rat primary chondrocytes were stimulated by hydrogen peroxide (H₂ O₂ , 300 μM). Histologic grading system was performed for detecting cartilage degeneration and immunohistochemistry for determining pyroptosis. The moleculars associated with cartilage homeostasis and inflammatory cytokines were analysed; moreover, the activation of NLRP3 inflammasome was determined. CF101 treatment significantly attenuated OA cartilage damage, OA-related pain and cartilage pyroptosis. Chondrocytes stimulated by H₂ O₂ evoked ROS release, thereby promoting the activation of NLRP3 inflammasome and facilitating the cleavage of GSDMD, which ultimately resulted in the mass release of pro-inflammatory cytokines including IL-1β and IL-18, and production of matrix hydrolase. The pre-treatment with CF101 powerfully inhibited the above process both in vivo and in vitro. Our findings demonstrated that activation of A3AR attenuates OA progression and relieves pain perception through suppression of cartilage degradation and inhibition of ROS/NLRP3/GSDMD signalling, indicating pyroptosis is a potential candidate for OA treatment.

Caffeine and rheumatoid arthritis: A complicated relationship

The current ideal goal of rheumatoid arthritis (RA) management is to resolve joint and systemic inflammation by using pharmacological interventions, assuming this will correspondingly lead to overall well-being. Nonetheless, it has emerged that a substantial number of RA patients do not reach optimal disease control. Thus suggesting the holistic management of subjective symptoms might be overlooked. This poses significant medical challenges; hence the proposal of incorporating lifestyle interventions as part of a multidimensional approach. Among these aspects, both patients and physicians perceive the important role of nutrition. This review shall examine how caffeine, one of the most studied bioactive components of the most widely consumed beverages, may potentially interfere with RA management. In particular, the mechanism by which caffeine affects RA pathogenesis, as a trigger for RA onset or flare, including its influence on rheumatic drug metabolism and the most common RA comorbidities and constitutional symptoms are outlined, highlighting important knowledge gaps and unmet research needs.

Cancer biology and molecular genetics of A3 adenosine receptor

A3 adenosine receptor (A3AR) is a cell membrane protein, which has been found to be overexpressed in a large number of cancer types. This receptor plays an important role in cancer by interacting with adenosine. Specifically, A3AR has a dual nature in different pathophysiological conditions, as it is expressed according to tissue type and stimulated by an adenosine dose-dependent manner. A3AR activation leads to tumor growth, cell proliferation and survival in some cases, while triggering cytostatic and apoptotic pathways in others. This review aims to describe the most relevant aspects of A3AR activation and its ligands whereas it summarizes A3AR activities in cancer. Progress in the field of A3AR modulators, with a potential therapeutic role in cancer treatment are reported, as well.

Acute visceral pain relief mediated by A3AR agonists in rats: involvement of N-type voltage-gated calcium channels

ABSTRACT

Pharmacological tools for chronic visceral pain management are still limited and inadequate. A3 adenosine receptor (A3AR) agonists are effective in different models of persistent pain. Recently, their activity has been related to the block of N-type voltage-gated Ca2+ channels (Cav2.2) in dorsal root ganglia (DRG) neurons. The present work aimed to evaluate the efficacy of A3AR agonists in reducing postinflammatory visceral hypersensitivity in both male and female rats. Colitis was induced by the intracolonic instillation of 2,4-dinitrobenzenesulfonic acid (DNBS; 30 mg in 0.25 mL 50% EtOH). Visceral hypersensitivity was assessed by measuring the visceromotor response and the abdominal withdrawal reflex to colorectal distension. The effects of A3AR agonists (MRS5980 and Cl-IB-MECA) were evaluated over time after DNBS injection and compared to that of the selective Cav2.2 blocker PD173212, and the clinically used drug linaclotide. A3AR agonists significantly reduced DNBS-evoked visceral pain both in the postinflammatory (14 and 21 days after DNBS injection) and persistence (28 and 35 days after DNBS) phases. Efficacy was comparable to effects induced by linaclotide. PD173212 fully reduced abdominal hypersensitivity to control values, highlighting the role of Cav2.2. The effects of MRS5980 and Cl-IB-MECA were completely abolished by the selective A3AR antagonist MRS1523. Furthermore, patch-clamp recordings showed that A3AR agonists inhibited Cav2.2 in dorsal root ganglia neurons isolated from either control or DNBS-treated rats. The effect on Ca2+ current was PD173212-sensitive and prevented by MRS1523. A3AR agonists are effective in relieving visceral hypersensitivity induced by DNBS, suggesting a potential therapeutic role against abdominal pain.

Synergic effects of extremely low-frequency electromagnetic field and betaine on in vitro osteogenic differentiation of human adipose tissue-derived mesenchymal stem cells

Human adipose tissue-derived mesenchymal stem cells (hADSCs) due to easy extraction, relative abundance, in vitro expansion and differentiation potential, frozen storage capability, and ability to secrete cytokines, compared to other stem cells, are appropriate candidate in regenerative medicine. Extremely low-frequency electromagnetic fields (ELF-EMF) and betaine are two safe factors in bone lesions repair. This study was designed to assess the osteogenic differentiation potential of these factors on hADSCs. The samples were collected from women undergoing liposuction after obtaining written consent. The hADSCs were extracted and treated with osteogenesis differentiation medium (OD) as the positive control, with OD and betaine (BET group), with OD and EMF (EMF group), and with OD and betaine and EMF (BET+EMF group) for 21 d; the negative control consisted of cells without treatment. Betaine 10 mM and EMF with 50-Hz frequency, 1-mT intensity (8 h daily), and in the form of sinus wave were used. Osteogenic differentiation was evaluated by Alizarin Red staining, alkaline phosphatase activity, calcium deposition, and real-time PCR. A significant increase in calcium deposition in the BET+EMF group was observed compared to the other groups. The activity of alkaline phosphatase in the positive control and BET groups was increased significantly compared to EMF and BET + EMF groups and a significant increase of this enzyme activity in the BET + EMF compared to EMF group was observed. The expression of RUNX2 and OCN genes in the EMF-treated groups were significantly reduced compared to the non-EMF-treated groups, and BET+EMF showed a significant increase of RUNX2 gene expression as compared the EMF group. The ELF-EMF leads to a decrease in the osteogenic differentiation and the expression RUNX2 and OCN genes in hADSCs. But osteogenic differentiation and RUNX2 gene expression were increased post-induction by betaine. The synergic effect of betaine and EMF on the osteogenic differentiation and related genes expression of hADSCs was higher than EMF.

Pulsed Electromagnetic Field Stimulation in Osteogenesis and Chondrogenesis: Signaling Pathways and Therapeutic Implications

Mesenchymal stem cells (MSCs) are the main cell players in tissue repair and thanks to their self-renewal and multi-lineage differentiation capabilities, they gained significant attention as cell source for tissue engineering (TE) approaches aimed at restoring bone and cartilage defects. Despite significant progress, their therapeutic application remains debated: the TE construct often fails to completely restore the biomechanical properties of the native tissue, leading to poor clinical outcomes in the long term. Pulsed electromagnetic fields (PEMFs) are currently used as a safe and non-invasive treatment to enhance bone healing and to provide joint protection. PEMFs enhance both osteogenic and chondrogenic differentiation of MSCs. Here, we provide extensive review of the signaling pathways modulated by PEMFs during MSCs osteogenic and chondrogenic differentiation. Particular attention has been given to the PEMF-mediated activation of the adenosine signaling and their regulation of the inflammatory response as key player in TE approaches. Overall, the application of PEMFs in tissue repair is foreseen: (1) in vitro: to improve the functional and mechanical properties of the engineered construct; (2) in vivo: (i) to favor graft integration, (ii) to control the local inflammatory response, and (iii) to foster tissue repair from both implanted and resident MSCs cells.

Perspectives of Methotrexate-Based Radioagents for Application in Nuclear Medicine

Methotrexate is a gold standard among disease modifying antirheumatic drugs and is also extensively used clinically in combination with oncological therapies. Thus, it is not surprising that nuclear medicine found an interest in methotrexate in the search for diagnostic and therapeutic solutions. Numerous folate-related radiopharmaceuticals have been proposed for nuclear medicine purposes; however, methotrexate radioagents represent only a minority. This imbalance results from the fact that methotrexate has significantly weaker affinity for folate receptors than folic acid. Nevertheless, radiolabeled methotrexate agents utilized as a tool for early detection and imaging of inflammation in rheumatoid arthritis patients gave promising results. Similarly, the use of multimodal MTX-release nanosystems may find potential applications in radiosynovectomy and theranostic approaches in folate receptor positive cancers.

A2A adenosine receptors are involved in the reparative response of tendon cells to pulsed electromagnetic fields

Tendinopathy is a degenerative disease in which inflammatory mediators have been found to be sometimes present. The interaction between inflammation and matrix remodeling in human tendon cells (TCs) is supported by the secretion of cytokines such as IL-1β, IL-6 and IL-33. In this context, it has been demonstrated that pulsed electromagnetic fields (PEMFs) were able to reduce inflammation and promote tendon marker synthesis. The aim of this study was to evaluate the anabolic and anti-inflammatory PEMF-mediated response on TCs in an in vitro model of inflammation. Moreover, since PEMFs enhance the anti-inflammatory efficacy of adenosine through the adenosine receptors (ARs), the study also focused on the role of A_2AARs. Human TCs were exposed to PEMFs for 48 hours. After stimulation, A_2AAR saturation binding experiments were performed. Along with 48 hours PEMF stimulation, TCs were treated with IL-1β and A_2AAR agonist CGS-21680. IL-1Ra, IL-6, IL-8, IL-10, IL-33, VEGF, TGF-β1, PGE₂ release and SCX, COL1A1, COL3A1, ADORA2A expression were quantified. PEMFs exerted A_2AAR modulation on TCs and promoted COL3A1 upregulation and IL-33 secretion. In presence of IL-1β, TCs showed an upregulation of ADORA2A, SCX and COL3A1 expression and an increase of IL-6, IL-8, PGE₂ and VEGF secretion. After PEMF and IL-1β exposure, IL-33 was upregulated, whereas IL-6, PGE₂ and ADORA2A were downregulated. These findings demonstrated that A_2AARs have a role in the promotion of the TC anabolic/reparative response to PEMFs and to IL-1β.

Adenosine Signaling in Autoimmune Disorders

The molecular components of the purinergic system (i.e., receptors, metabolizing enzymes and membrane transporters) are widely expressed in the cells of the immune system. Additionally, high concentrations of adenosine are generated from the hydrolysis of ATP in any "danger" condition, when oxygen and energy availability dramatically drops. Therefore, adenosine acts as a retaliatory metabolite to counteract the nucleotide-mediated boost of the immune reaction. Based on this observation, it can be foreseen that the recruitment with selective agonists of the receptors involved in the immunomodulatory effect of adenosine might represent an innovative anti-inflammatory approach with potential exploitation in autoimmune disorders. Quite surprisingly, pro-inflammatory activity exerted by some adenosine receptors has been also identified, thus paving the way for the hypothesis that at least some autoimmune disorders may be caused by a derailment of adenosine signaling. In this review article, we provide a general overview of the roles played by adenosine on immune cells with a specific focus on the development of adenosine-based therapies for autoimmune disorders, as demonstrated by the exciting data from concluded and ongoing clinical trials.

Overview of Dual-Acting Drug Methotrexate in Different Neurological Diseases, Autoimmune Pathologies and Cancers

Methotrexate, a structural analogue of folic acid, is one of the most effective and extensively used drugs for treating many kinds of cancer or severe and resistant forms of autoimmune diseases. In this paper, we take an overview of the present state of knowledge with regards to complex mechanisms of methotrexate action and its applications as immunosuppressive drug or chemotherapeutic agent in oncological combination therapy. In addition, the issue of the potential benefits of methotrexate in the development of neurological disorders in Alzheimer’s disease or myasthenia gravis will be discussed.

Role and Function of Adenosine and its Receptors in Inflammation, Neuroinflammation, IBS, Autoimmune Inflammatory Disorders, Rheumatoid Arthritis and Psoriasis

The physiological effects of endogenous adenosine on various organ systems are very complex and numerous which are elicited upon activation of any of the four G-protein-coupled receptors (GPCRs) denoted as A1, A2A, A2B and A3 adenosine receptors (ARs). Several fused heterocyclic and non-xanthine derivatives are reported as a possible target for these receptors due to physiological problems and lack of selectivity of xanthine derivatives. In the present review, we have discussed the development of various new chemical entities as a target for these receptors. In addition, compounds acting on adenosine receptors can be utilized in treating diseases like inflammation, neuroinflammation, autoimmune and related diseases.

Signaling of the Purinergic System in the Joint

The joint is a complex anatomical structure consisting of different tissues, each with a particular feature, playing together to give mobility and stability at the body. All the joints have a similar composition including cartilage for reducing the friction of the movement and protecting the underlying bone, a synovial membrane that produces synovial fluid to lubricate the joint, ligaments to limit joint movement, and tendons for the interaction with muscles. Direct or indirect damage of one or more of the tissues forming the joint is the foundation of different pathological conditions. Many molecular mechanisms are involved in maintaining the joint homeostasis as well as in triggering disease development. The molecular pathway activated by the purinergic system is one of them.The purinergic signaling defines a group of receptors and intermembrane channels activated by adenosine, adenosine diphosphate, adenosine 5’-triphosphate, uridine triphosphate, and uridine diphosphate. It has been largely described as a modulator of many physiological and pathological conditions including rheumatic diseases. Here we will give an overview of the purinergic system in the joint describing its expression and function in the synovium, cartilage, ligament, tendon, and bone with a therapeutic perspective.

ATP and adenosine: Role in the immunopathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a classic inflammatory autoimmune disease. Local joint destruction and extra-articular manifestations of RA deeply compromise the life quality of the affected patients. RA immunopathogenesis depends on continuous immunogenic activation in which the purinergic system participates. The purinergic system comprises the signaling and metabolism of purines such as adenosine triphosphate (ATP) and adenosine. ATP signaling is involved in the activation and maintenance of the inflammatory state of RA through the activation of P2X7 and the production of cytokines, which orchestrate the pathogenesis of RA. The breakdown of ATP through the CD39/CD73 axis produces adenosine, which mostly inhibits the inflammatory process through activation of specific P1 receptors. Adenosine is hydrolyzed by adenosine deaminase (ADA) that interacts with other molecules playing additional roles in this disease. This review explores the release, metabolism, and the effects of binding of ATP and adenosine to their respective receptors in the context of RA, as well as their potential use as biomarkers and therapeutic targets.

Novel Hybrid Gels Made of High and Low Molecular Weight Hyaluronic Acid Induce Proliferation and Reduce Inflammation in an Osteoarthritis In Vitro Model Based on Human Synoviocytes and Chondrocytes

High molecular weight hyaluronan (H-HA) has a pivotal role in the maintenance of normal functions of synovial fluid and structure of the articular joint, but it has been shown that its concentration is reduced in patients affected by degenerative cartilage diseases, such as osteoarthritis (OA). The aim of this study was to investigate the anti-inflammatory effects and properties of hybrid cooperative complexes based on high and low molecular weight hyaluronan (HCC) compared to H-HA on human primary cells derived by pathological joints. In addition, the rheological behavior of HCC was evaluated in order to define their potential as viscosupplement gel in degenerated joints. The experiments were performed using an in vitro model of OA based on human chondrocytes and synoviocytes isolated from degenerated joints of patients hospitalized for surgical replacement. In order to assess the anti-inflammatory effects of HCC, we evaluated NF-kB, COMP-2, IL-6, and IL-8 as specific markers at the transcriptional and/or protein level. Moreover, the proliferative properties of HCC were assessed using time lapse video microscopy. We showed that chondrocytes and synoviocytes clearly presented an altered cytokine profile compatible with a severe ongoing inflammation status. H-HA and, above all, HCC significantly reduced levels of the specific biomarkers evaluated and improved cartilage healing. The rheological profile indicated HCC suitability for intra-articular injection in joint diseases. HCC viscoelastic properties and the protective/anti-inflammatory effect on human chondrocytes and synoviocytes suggest the novel HCC-based gels as a valid support for OA management.

Physical Stimulations for Bone and Cartilage Regeneration

A wide range of techniques and methods are actively invented by clinicians and scientists who are dedicated to the field of musculoskeletal tissue regeneration. Biological, chemical, and physiological factors, which play key roles in musculoskeletal tissue development, have been extensively explored. However, physical stimulation is increasingly showing extreme importance in the processes of osteogenic and chondrogenic differentiation, proliferation and maturation through defined dose parameters including mode, frequency, magnitude, and duration of stimuli. Studies have shown manipulation of physical microenvironment is an indispensable strategy for the repair and regeneration of bone and cartilage, and biophysical cues could profoundly promote their regeneration. In this article, we review recent literature on utilization of physical stimulation, such as mechanical forces (cyclic strain, fluid shear stress, etc.), electrical and magnetic fields, ultrasound, shock waves, substrate stimuli, etc., to promote the repair and regeneration of bone and cartilage tissue. Emphasis is placed on the mechanism of cellular response and the potential clinical usage of these stimulations for bone and cartilage regeneration.

A3 Adenosine Receptors as Modulators of Inflammation: From Medicinal Chemistry to Therapy

The A3 adenosine receptor (A3 AR) subtype is a novel, promising therapeutic target for inflammatory diseases, such as rheumatoid arthritis (RA) and psoriasis, as well as liver cancer. A3 AR is coupled to inhibition of adenylyl cyclase and regulation of mitogen-activated protein kinase (MAPK) pathways, leading to modulation of transcription. Furthermore, A3 AR affects functions of almost all immune cells and the proliferation of cancer cells. Numerous A3 AR agonists, partial agonists, antagonists, and allosteric modulators have been reported, and their structure-activity relationships (SARs) have been studied culminating in the development of potent and selective molecules with drug-like characteristics. The efficacy of nucleoside agonists may be suppressed to produce antagonists, by structural modification of the ribose moiety. Diverse classes of heterocycles have been discovered as selective A3 AR blockers, although with large species differences. Thus, as a result of intense basic research efforts, the outlook for development of A3 AR modulators for human therapeutics is encouraging. Two prototypical selective agonists, N6-(3-Iodobenzyl)adenosine-5'-N-methyluronamide (IB-MECA; CF101) and 2-chloro-N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (Cl-IB-MECA; CF102), have progressed to advanced clinical trials. They were found safe and well tolerated in all preclinical and human clinical studies and showed promising results, particularly in psoriasis and RA, where the A3 AR is both a promising therapeutic target and a biologically predictive marker, suggesting a personalized medicine approach. Targeting the A3 AR may pave the way for safe and efficacious treatments for patient populations affected by inflammatory diseases, cancer, and other conditions.

Adenosine Receptors As Drug Targets for Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a clinical condition characterized by pulmonary arterial remodeling and vasoconstriction, which promote chronic vessel obstruction and elevation of pulmonary vascular resistance. Long-term right ventricular (RV) overload leads to RV dysfunction and failure, which are the main determinants of life expectancy in PAH subjects. Therapeutic options for PAH remain limited, despite the introduction of prostacyclin analogs, endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, and soluble guanylyl cyclase stimulators within the last 15 years. Through addressing the pulmonary endothelial and smooth muscle cell dysfunctions associated with PAH, these interventions delay disease progression but do not offer a cure. Emerging approaches to improve treatment efficacy have focused on beneficial actions to both the pulmonary vasculature and myocardium, and several new targets have been investigated and validated in experimental PAH models. Herein, we review the effects of adenosine and adenosine receptors (A₁, A_2A, A_2B, and A₃) on the cardiovascular system, focusing on the A_2A receptor as a pharmacological target. This receptor induces pulmonary vascular and heart protection in experimental models, specifically models of PAH. Targeting the A_2A receptor could potentially serve as a novel and efficient approach for treating PAH and concomitant RV failure. A_2A receptor activation induces pulmonary endothelial nitric oxide synthesis, smooth muscle cell hyperpolarization, and vasodilation, with important antiproliferative activities through the inhibition of collagen deposition and vessel wall remodeling in the pulmonary arterioles. The pleiotropic potential of A_2A receptor activation is highlighted by its additional expression in the heart tissue, where it participates in the regulation of intracellular calcium handling and maintenance of heart chamber structure and function. In this way, the activation of A_2A receptor could prevent the production of a hypertrophic and dysfunctional phenotype in animal models of cardiovascular diseases.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.

Synovial membrane receptors as therapeutic targets: A review of receptor localization, structure, and function

Joint pathology and degeneration is a significant cause of pain. The synovial membrane plays an important role in maintenance of the joint, contributes to the pathology of many arthropathies and may be adversely affected in joint disease. Improving knowledge of the receptors present within the synovium will aid in a better understanding of joint pathology and the development of new treatments for diseases such as osteoarthritis and rheumatoid arthritis. Knowledge of the location and function of synovial membrane receptors (both in healthy and diseased synovium) may provide important targets in the treatment of various arthropathies. Classic pain receptors such as opioid receptors in the synovium are a mainstay in local and systemic management of chronic pain in many species. In addition to these, many other receptors such as bradykinin, neurokinin, transient receptor potential vanilloid, and inflammatory receptors, such as prostanoid and interleukin receptors have been discovered within the synovial membrane. These receptors are important in pain, inflammation, and in maintenance of normal joint function and may serve as targets for pharmacologic intervention in pathologic states. The goal of this review is to outline synovial membrane receptor localization and local therapeutic modulation of these receptors, in order to stimulate further research into pharmacological management of arthropathies at the local level. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1589-1605, 2017.

Adenosine Receptors as a Biological Pathway for the Anti-Inflammatory and Beneficial Effects of Low Frequency Low Energy Pulsed Electromagnetic Fields

Several studies explored the biological effects of low frequency low energy pulsed electromagnetic fields (PEMFs) on human body reporting different functional changes. Much research activity has focused on the mechanisms of interaction between PEMFs and membrane receptors such as the involvement of adenosine receptors (ARs). In particular, PEMF exposure mediates a significant upregulation of A_2A and A₃ARs expressed in various cells or tissues involving a reduction in most of the proinflammatory cytokines. Of particular interest is the observation that PEMFs, acting as modulators of adenosine, are able to increase the functionality of the endogenous agonist. By reviewing the scientific literature on joint cells, a double role for PEMFs could be hypothesized in vitro by stimulating cell proliferation, colonization of the scaffold, and production of tissue matrix. Another effect could be obtained in vivo after surgical implantation of the construct by favoring the anabolic activities of the implanted cells and surrounding tissues and protecting the construct from the catabolic effects of the inflammatory status. Moreover, a protective involvement of PEMFs on hypoxia damage in neuron-like cells and an anti-inflammatory effect in microglial cells have suggested the hypothesis of a positive impact of this noninvasive biophysical stimulus.

RAW 264.7 co-cultured with ultra-high molecular weight polyethylene particles spontaneously differentiate into osteoclasts: an in vitro model of periprosthetic osteolysis

Wear-particle osteolysis affects prosthesis survival leading to implant loosening up to 70% of revisions. Therapeutic strategies are increasing, however alternative testing methods to experimentally evaluate such treatments are lacking. The aim of this study was to reproduce an in vitro osteolysis model recapitulating the events that, starting from the exposure of macrophages to polyethylene, lead to the establishment of osteoclastogenesis and inflammation. Responses to polyethylene, at 3 and 7 days, in a macrophage cell line, RAW 264.7, were determined by DNA quantification, immunofluorescence, pit assay, gene expression, cytokine production and NF-kB activation. Results showed that 3 days exposure to particles could induce a significant production of Tumor Necrosis Factor alpha (p < 0.0005) and Prostaglandin E₂ (p < 0.005) compared to controls. Particles also induced macrophages to spontaneously differentiate into mature and active osteoclasts, in terms of identification of multinucleated cells by Phalloidin staining and by the analysis of osteoclast-specific gene markers. In particular, at 3 days polyethylene induced a significant up-regulation of Nuclear Factor of Activated T-cells, cytoplasmic 1, Receptor Activator of Nuclear factor Kappa-B and Receptor Activator of Nuclear Factor Kappa-B Ligand genes (p < 0.0005) compared to controls. At protein level, the particles induced a significant increase of Receptor Activator of Nuclear Factor Kappa-B Ligand at day 7 over controls (p < 0.0005). Osteoclasts were capable to resorb bone even in absence of differentiating factors. The possible mechanism, beside spontaneous osteoclastogenesis mediated by wear debris, was identified in an autocrine up-regulation of Receptor activator of nuclear factor kappa-B ligand gene expression and protein synthesis. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 510-520, 2017.

Renoprotective Effects of a Highly Selective A3 Adenosine Receptor Antagonist in a Mouse Model of Adriamycin-induced Nephropathy

The concentration of adenosine in the normal kidney increases markedly during renal hypoxia, ischemia, and inflammation. A recent study reported that an A3 adenosine receptor (A3AR) antagonist attenuated the progression of renal fibrosis. The adriamycin (ADX)-induced nephropathy model induces podocyte injury, which results in severe proteinuria and progressive glomerulosclerosis. In this study, we investigated the preventive effect of a highly selective A3AR antagonist (LJ1888) in ADX-induced nephropathy. Three groups of six-week-old Balb/c mice were treated with ADX (11 mg/kg) for four weeks and LJ1888 (10 mg/kg) for two weeks as following: 1) control; 2) ADX; and 3) ADX + LJ1888. ADX treatment decreased body weight without a change in water and food intake, but this was ameliorated by LJ1888 treatment. Interestingly, LJ1888 lowered plasma creatinine level, proteinuria, and albuminuria, which had increased during ADX treatment. Furthermore, LJ1888 inhibited urinary nephrin excretion as a podocyte injury marker, and urine 8-isoprostane and kidney lipid peroxide concentration, which are markers of oxidative stress, increased after injection of ADX. ADX also induced the activation of proinflammatory and profibrotic molecules such as TGF-β1, MCP-1, PAI-1, type IV collagen, NF-κB, NOX4, TLR4, TNFα, IL-1β, and IFN-γ, but they were remarkably suppressed after LJ1888 treatment. In conclusion, our results suggest that LJ1888 has a renoprotective effect in ADX-induced nephropathy, which might be associated with podocyte injury through oxidative stress. Therefore, LJ1888, a selective A3AR antagonist, could be considered as a potential therapeutic agent in renal glomerular diseases which include podocyte injury and proteinuria.

Identification of A3 adenosine receptor agonists as novel non-narcotic analgesics

Chronic pain negatively impacts the quality of life in a variety of patient populations. The current therapeutic repertoire is inadequate in managing patient pain and warrants the development of new therapeutics. Adenosine and its four cognate receptors (A1 , A2A , A2B and A3 ) have important roles in physiological and pathophysiological states, including chronic pain. Preclinical and clinical studies have revealed that while adenosine and agonists of the A1 and A2A receptors have antinociceptive properties, their therapeutic utility is limited by adverse cardiovascular side effects. In contrast, our understanding of the A3 receptor is only in its infancy, but exciting preclinical observations of A3 receptor antinociception, which have been bolstered by clinical trials of A3 receptor agonists in other disease states, suggest pain relief without cardiovascular side effects and with sufficient tolerability. Our goal herein is to briefly discuss adenosine and its receptors in the context of pathological pain and to consider the current data regarding A3 receptor-mediated antinociception. We will highlight recent findings regarding the impact of the A3 receptor on pain pathways and examine the current state of selective A3 receptor agonists used for these studies. The adenosine-to-A3 receptor pathway represents an important endogenous system that can be targeted to provide safe, effective pain relief from chronic pain.

Selective A3 adenosine receptor agonist protects against doxorubicin-induced cardiotoxicity

PURPOSE

Doxorubicin (DOX) is an effective anticancer drug; however, its clinical use is limited by its cardiotoxic effect. Adenosine was proved to mediate anti-inflammatory effects and protected from myocardial ischemia/reperfusion injury. So the present work was designed to examine the effectiveness of a selective A3 adenosine receptor agonist (Cl-IB-MECA) in DOX-induced cardiotoxicity and to elucidate the underlying mechanisms via studying its effect on different oxidative stress, inflammatory and apoptotic markers.

METHODS

Firstly the potential cardioprotective dose of Cl-IB-MECA was screened in male Wistar rats at different doses (20, 40 and 80 µg/kg; i.v) against a single dose of DOX (15 mg/kg; i.p). Secondly, the dose of 40 µg/kg Cl-IB-MECA was selected for further assessment of the cardioprotective mechanisms.

RESULTS

Cl-IB-MECA at a dose 40 µg/kg (i.v) protects against DOX-induced bradycardia, elevated creatine kinase isoenzyme-MB and histopathological changes. Also, it significantly ameliorates oxidative stress injury evoked by DOX as evidenced by inhibition of reduced glutathione depletion and lipid peroxidation as well as elevation of antioxidant enzyme activities. Additionally, DOX provoked inflammatory responses by increasing the expressions of nuclear factor kappa B and the levels of tumor necrosis factor alpha. Cl-IB-MECA pretreatment significantly inhibited these inflammatory responses. Furthermore, DOX induced apoptotic tissue damage by increasing cytochrome c expressions which was suppressed by Cl-IB-MECA pretreatment.

CONCLUSION

Cl-IB-MECA protects against DOX-induced cardiotoxicity through restoration of the oxidant/antioxidant status and consequential suppression of DOX-induced inflammatory responses and abrogation of the resultant apoptotic signals.

Design, synthesis, and biological evaluation of novel 2-((2-(4-(substituted)phenylpiperazin-1-yl)ethyl)amino)-5'-N-ethylcarboxamidoadenosines as potent and selective agonists of the A2A adenosine receptor

Stimulation of A2A adenosine receptors (AR) promotes anti-inflammatory responses in animal models of allergic rhinitis, asthma, chronic obstructive pulmonary disease, and rheumatic diseases. Herein we describe the results of a research program aimed at identifying potent and selective agonists of the A2AAR as potential anti-inflammatory agents. The recent crystallographic analysis of A2AAR agonists and antagonists in complex with the receptor provided key information on the structural determinants leading to receptor activation or blocking. In light of this, we designed a new series of 2-((4-aryl(alkyl)piperazin-1-yl)alkylamino)-5'-N-ethylcarboxamidoadenosines with high A2AAR affinity, activation potency and selectivity obtained by merging distinctive structural elements of known agonists and antagonists of the investigated target. Docking-based SAR optimization allowed us to identify compound 42 as one of the most potent and selective A2A agonist discovered so far (Ki hA2AAR = 4.8 nM, EC50 hA2AAR = 4.9 nM, Ki hA1AR > 10 000 nM, Ki hA3AR = 1487 nM, EC50 hA2BAR > 10 000 nM).

An adenosine A3 receptor agonist inhibits DSS-induced colitis in mice through modulation of the NF-κB signaling pathway

The role of the adenosine A3 receptor (A3AR) in experimental colitis is controversial. The A3AR agonist N⁶-(3-iodobenzyl)adenosine-5'-N-methyluronamide (IB-MECA) has been shown to have a clinical benefit, although studies in A3AR-deficient mice suggest a pro-inflammatory role. However, there are no studies on the effect of 2-Cl-IB-MECA and the molecular mechanism of action of A3AR in murine colitis models in vivo. Is it the same as that observed in vitro? The interaction between 2-CL-IB-MECA and A3AR in a murine colitis model and the signaling pathways associated with this interaction remain unclear. Here we demonstrate a role for the NF-κB signaling pathway and its effect on modifying the activity of proinflammatory factors in A3AR-mediated biological processes. Our results demonstrated that A3AR activation possessed marked effects on experimental colitis through the NF-κB signaling pathway.

Spinal neuroimmune activation is independent of T-cell infiltration and attenuated by A3 adenosine receptor agonists in a model of oxaliplatin-induced peripheral neuropathy

Many commonly used chemotherapeutics including oxaliplatin are associated with the development of a painful chemotherapy-induced peripheral neuropathy (CIPN). This dose-limiting complication can appear long after the completion of therapy causing a significant reduction in quality-of-life and impeding cancer treatment. We recently reported that activation of the Gi/Gq-coupled A3 adenosine receptor (A3AR) with selective A3AR agonists (i.e., IB-MECA) blocked the development of chemotherapy induced-neuropathic pain in models evoked by distinct agents including oxaliplatin without interfering with their anticancer activities. The mechanism(s) of action underlying these beneficial effects has yet to be explored. Our results herein demonstrate that the development of oxaliplatin-induced mechano-hypersensitivity (allodynia and hyperalgesia) in rats is associated with the hyperactivation of astrocytes, but not microglial cells, increased production of pro-inflammatory and neuroexcitatory cytokines (TNF, IL-1β), and reductions in the levels of anti-inflammatory/neuroprotective cytokines (IL-10, IL-4) in the dorsal horn of the spinal cord. These events did not require lymphocytic mobilization since oxaliplatin did not induce CD45(+)/CD3(+) T-cell infiltration into the spinal cord. A3AR agonists blocked the development of neuropathic pain with beneficial effects strongly associated with the modulation of spinal neuroinflammatory processes: attenuation of astrocytic hyperactivation, inhibition of TNF and IL-1β production, and an increase in IL-10 and IL-4. These results suggest that inhibition of an astrocyte-associated neuroinflammatory response contributes to the protective actions of A3AR signaling and continues to support the pharmacological basis for selective A3AR agonists as adjuncts to chemotherapeutic agents for the management of chronic pain.

The A3 adenosine receptor: history and perspectives

By general consensus, the omnipresent purine nucleoside adenosine is considered a major regulator of local tissue function, especially when energy supply fails to meet cellular energy demand. Adenosine mediation involves activation of a family of four G protein-coupled adenosine receptors (ARs): A(1), A(2)A, A(2)B, and A(3). The A(3) adenosine receptor (A(3)AR) is the only adenosine subtype to be overexpressed in inflammatory and cancer cells, thus making it a potential target for therapy. Originally isolated as an orphan receptor, A(3)AR presented a twofold nature under different pathophysiologic conditions: it appeared to be protective/harmful under ischemic conditions, pro/anti-inflammatory, and pro/antitumoral depending on the systems investigated. Until recently, the greatest and most intriguing challenge has been to understand whether, and in which cases, selective A(3) agonists or antagonists would be the best choice. Today, the choice has been made and A(3)AR agonists are now under clinical development for some disorders including rheumatoid arthritis, psoriasis, glaucoma, and hepatocellular carcinoma. More specifically, the interest and relevance of these new agents derives from clinical data demonstrating that A(3)AR agonists are both effective and safe. Thus, it will become apparent in the present review that purine scientists do seem to be getting closer to their goal: the incorporation of adenosine ligands into drugs with the ability to save lives and improve human health.

Pulsed electromagnetic fields stimulate osteogenic differentiation in human bone marrow and adipose tissue derived mesenchymal stem cells

Pulsed electromagnetic fields (PEMFs) play a regulatory role on osteoblast activity and are clinically beneficial during fracture healing. Human mesenchymal stem cells (MSCs) derived from different sources have been extensively used in bone tissue engineering. Compared with MSCs isolated from bone marrow (BMSCs), those derived from adipose tissue (ASCs) are easier to obtain and available in larger amounts, although they show a less osteogenic differentiation potential than BMSCs. The hypothesis tested in this study was to evaluate whether PEMFs favor osteogenic differentiation both in BMSCs and in ASCs and to compare the role of PEMFs alone and in combination with the biochemical osteogenic stimulus bone morphogenetic protein (BMP)-2. Early and later osteogenic markers, such as alkaline phosphatase (ALP) activity, osteocalcin levels, and matrix mineralization, were analyzed at different times during osteogenic differentiation. Results showed that PEMFs induced osteogenic differentiation by increasing ALP activity, osteocalcin, and matrix mineralization in both BMSCs and ASCs, suggesting that PEMF activity is maintained during the whole differentiation period. The addition of BMP-2 in PEMF exposed cultures further increased all the osteogenic markers in BMSCs, while in ASCs, the stimulatory role of PEMFs was independent of BMP-2. Our results indicate that PEMFs may stimulate an early osteogenic induction in both BMSCs and ASCs and they suggest PEMFs as a bioactive factor to enhance the osteogenesis of ASCs, which are an attractive cell source for clinical applications. In conclusion, PEMFs may be considered a possible tool to improve autologous cell-based regeneration of bone defects in orthopedics.

Effect of pulsed electromagnetic field therapy in patients undergoing total knee arthroplasty: a randomised controlled trial

Purpose

It has been reported that even one year after total knee arthroplasty (TKA), a relevant percentage of patients does not attain complete recovery and indicate unfavourable long-term pain outcome. We compared the clinical outcome of 33 patients undergoing TKA randomly assigned to the control or the pulsed electromagnetic field group (I-ONE therapy).

Methods

I-ONE therapy was administered postoperatively four hours per day for 60 days. Patients were assessed before surgery and then at one, two and six months postoperatively using international scores.

Results

One month after TKA, pain, knee swelling and functional score were significantly better in the treated compared with the control group. Pain was still significantly lower in the treated group at the six month follow-up. Three years after surgery, severe pain and occasional walking limitations were reported in a significantly lower number of patients in the treated group.

Conclusions

Advantages deriving from early control of joint inflammation may explain the maintenance of results at follow-up. I-ONE therapy should be considered an effective completion of the TKA procedure.

Purinergic signalling in the musculoskeletal system

It is now widely recognised that extracellular nucleotides, signalling via purinergic receptors, participate in numerous biological processes in most tissues. It has become evident that extracellular nucleotides have significant regulatory effects in the musculoskeletal system. In early development, ATP released from motor nerves along with acetylcholine acts as a cotransmitter in neuromuscular transmission; in mature animals, ATP functions as a neuromodulator. Purinergic receptors expressed by skeletal muscle and satellite cells play important pathophysiological roles in their development or repair. In many cell types, expression of purinergic receptors is often dependent on differentiation. For example, sequential expression of P2X5, P2Y1 and P2X2 receptors occurs during muscle regeneration in the mdx model of muscular dystrophy. In bone and cartilage cells, the functional effects of purinergic signalling appear to be largely negative. ATP stimulates the formation and activation of osteoclasts, the bone-destroying cells. Another role appears to be as a potent local inhibitor of mineralisation. In osteoblasts, the bone-forming cells, ATP acts via P2 receptors to limit bone mineralisation by inhibiting alkaline phosphatase expression and activity. Extracellular ATP additionally exerts significant effects on mineralisation via its hydrolysis product, pyrophosphate. Evidence now suggests that purinergic signalling is potentially important in several bone and joint disorders including osteoporosis, rheumatoid arthritis and cancers. Strategies for future musculoskeletal therapies might involve modulation of purinergic receptor function or of the ecto-nucleotidases responsible for ATP breakdown or ATP transport inhibitors.

Multiple sclerosis lymphocytes upregulate A2A adenosine receptors that are antiinflammatory when stimulated

Multiple sclerosis (MS) is an autoimmune-mediated inflammatory disease characterized by multifocal areas of demyelination. Experimental evidence indicates that A2A adenosine receptors (ARs) play a pivotal role in the inhibition of inflammatory processes. The aim of this study was to investigate the contribution of A2A ARs in the inhibition of key pro-inflammatory mediators for the pathogenesis of MS. In lymphocytes from MS patients, A1, A2A, A2B, and A3 ARs were analyzed by using RT-PCR, Western blotting, immunofluorescence, and binding assays. Moreover the effect of A2A AR stimulation on proinflammatory cytokine release such as TNF-α, IFN-γ, IL-6, IL-1β, IL-17, and on lymphocyte proliferation was evaluated. The capability of an A2A AR agonist on the modulation of very late antigen (VLA)-4 expression and NF-κB was also explored. A2A AR upregulation was observed in lymphocytes from MS patients in comparison with healthy subjects. The stimulation of these receptors mediated a significant inhibition of TNF-α, IFN-γ, IL-6, IL-1β, IL-17, and cell proliferation as well as VLA-4 expression and NF-κB activation. This new evidence highlights that A2A AR agonists could represent a novel therapeutic tool for MS treatment as suggested by the antiinflammatory role of A2A ARs in lymphocytes from MS patients.

Pulsed electromagnetic fields increased the anti-inflammatory effect of A₂A and A₃ adenosine receptors in human T/C-28a2 chondrocytes and hFOB 1.19 osteoblasts

Adenosine receptors (ARs) have an important role in the regulation of inflammation and their activation is involved in the inhibition of pro-inflammatory cytokine release. The effects of pulsed electromagnetic fields (PEMFs) on inflammation have been reported and we have demonstrated that PEMFs increased A_2A and A₃AR density and functionality in different cell lines. Chondrocytes and osteoblasts are two key cell types in the skeletal system that play important role in cartilage and bone metabolism representing an interesting target to study the effect of PEMFs. The primary aim of the present study was to evaluate if PEMF exposure potentiated the anti-inflammatory effect of A_2A and/or A₃ARs in T/C-28a2 chondrocytes and hFOB 1.19 osteoblasts. Immunofluorescence, mRNA analysis and saturation binding assays revealed that PEMF exposure up-regulated A_2A and A₃AR expression. A_2A and A₃ARs were able to modulate cAMP production and cell proliferation. The activation of A_2A and A₃ARs resulted in the decrease of some of the most relevant pro-inflammatory cytokine release such as interleukin (IL)-6 and IL-8, following the treatment with IL-1β as an inflammatory stimuli. In human chondrocyte and osteoblast cell lines, the inhibitory effect of A_2A and A₃AR stimulation on the release of prostaglandin E₂ (PGE₂), an important lipid inflammatory mediator, was observed. In addition, in T/C-28a2 cells, the activation of A_2A or A₃ARs elicited an inhibition of vascular endothelial growth factor (VEGF) secretion. In hFOB 1.19 osteoblasts, PEMF exposure determined an increase of osteoprotegerin (OPG) production. The effect of the A_2A or A₃AR agonists in the examined cells was enhanced in the presence of PEMFs and completely blocked by using well-known selective antagonists. These results demonstrated that PEMF exposure significantly increase the anti-inflammatory effect of A_2A or A₃ARs suggesting their potential therapeutic use in the therapy of inflammatory bone and joint disorders.

A2A adenosine receptors are up-regulated in lymphocytes from amyotrophic lateral sclerosis patients

Adenosine, a purine nucleoside interacting with A1, A2A, A2B and A3 adenosine receptors (ARs), is a potent endogenous modulator of inflammatory and neuronal processes involved in the pathophysiology of several neurodegenerative diseases. In the present study, ARs were investigated in lymphocytes from patients with amyotrophic lateral sclerosis (ALS) and compared with age-matched healthy subjects. In ALS patients A2AARs were analysed by using RT-PCR, Western blotting and saturation binding experiments. The effect of A2AAR stimulation on cyclic AMP levels was evaluated in lymphocytes from ALS patients and healthy subjects. An up-regulation of A2AARs was observed in ALS patients with respect to healthy subjects while A1, A2B and A3AR affinity and density did not change. In ALS patients, the A2AAR density values correlated with the Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) scores. Furthermore, the stimulation of A2AARs mediated a significant increase in cyclic AMP levels in lymphocytes from ALS patients, with a higher potency than in lymphocytes from healthy subjects. In conclusion, the positive correlation between A2AAR density and ALSFRS-R scores could indicate a possible protective effect of this receptor subtype, representing an interesting starting point for the study of alternative therapeutic approaches for ALS based on A2AAR modulation.

TNF inhibitors induce discoid fibrosis in the sublining layers of the synovium with degeneration of synoviocytes in rheumatoid arthritis

We determined the characteristic features of synovial tissues of rheumatoid arthritis (RA) patients treated by TNF inhibitors in order to delineate their mechanism of action. Synovial tissues were obtained during the joint surgical operations from 12 RA patients who had been treated with TNF inhibitors in addition to disease modifying antirheumatic drugs (DMARDs) for at least 5 months (5-25 months) (RA-TNFinh), and from 12 RA patients who had been treated with DMARDs alone (RA-DMARD), and were evaluated under light microscopy. There were no significant differences in disease duration, serum CRP levels, DAS28, Steinbrocker's stages on X-ray and treatment regimen except for TNF inhibitors between RA-TNFinh and RA-DMARD. The most prominent changes in the synovium from RA-TNFinh were discoid fibrosis in the subliming layers of the synovium with degeneration and detachment of synoviocytes and marked decrease in vasculatures. There was no significant difference in these synovial features between RA patients with infliximab and those with etanercept. Interestingly, appearance of osteoclasts was observed in RA-TNFinh (3 out of 12 patients) and in RA-DMARD (1 out of 12 patients). These results indicate that not only infliximab, but etanercept might have direct actions on synovial cells in the deep lining layers of the synovium, leading to the discoid fibrosis thereof. Moreover, the data confirm that the deep lining or sublining layers of the synovium are the most important portions that steer the disease process of RA synovitis.

A(2A) adenosine receptors are differentially modulated by pharmacological treatments in rheumatoid arthritis patients and their stimulation ameliorates adjuvant-induced arthritis in rats

A_2A adenosine receptors (ARs) play a key role in the inhibition of the inflammatory process. The purpose of this study was to evaluate the modulation of A_2AARs in rheumatoid arthritis (RA) patients after different pharmacological treatments and to investigate the effect of A_2AAR stimulation in a rat model of arthritis. We investigated A_2AAR density and functionality in RA progression by using a longitudinal study in RA patients before and after methotrexate (MTX), anti-TNFα agents or rituximab treatments. A_2AARs were analyzed by saturation binding assays in lymphocytes from RA patients throughout the 24-month study timeframe. In an adjuvant-induced arthritis model in rats we showed the efficacy of the A_2AAR agonist, CGS 21680 in comparison with standard therapies by means of paw volume assessment, radiographic and ultrasonographic imaging. Arthritic-associated pain was investigated in mechanical allodynia and thermal hyperalgesia tests. IL-10 release following A_2AAR stimulation in lymphocytes from RA patients and in serum from arthritic rats was measured. In lymphocytes obtained from RA patients, the A_2AAR up-regulation was gradually reduced in function of the treatment time and the stimulation of these receptors mediated a significant increase of IL-10 production. In the same cells, CGS 21680 did not affected cell viability and did not produced cytotoxic effects. The A_2AAR agonist CGS 21680 was highly effective, as suggested by the marked reduction of clinical signs, in rat adjuvant-induced arthritis and associated pain. This study highlighted that A_2AAR agonists represent a physiological-like therapeutic alternative for RA treatment as suggested by the anti-inflammatory role of A_2AARs in lymphocytes from RA patients. The effectiveness of A_2AAR stimulation in a rat model of arthritis supported the role of A_2AAR agonists as potential pharmacological treatment for RA.

Electromagnetic fields counteract IL-1β activity during chondrogenesis of bovine mesenchymal stem cells

Osteoarthritis (OA) is a common joint disease associated with articular cartilage degeneration. To improve the therapeutic options of OA, tissue engineering based on the use of mesenchymal stem cells (MSCs) has emerged. However, the presence of inflammatory cytokines, such as interleukin-1β (IL-1β), during chondrogenesis reduces the efficacy of cartilage engineering repair procedures by preventing chondrogenic differentiation. Previous studies have shown that electromagnetic fields (EMFs) stimulate anabolic processes in OA cartilage and limit IL-1β catabolic effects. We investigated the role of EMFs during chondrogenic differentiation of MSCs, isolated from bovine synovial fluid, in the absence and presence of IL-1β. Pellets of MSCs were differentiated for 3 and 5 weeks with transforming growth factor-β3 (TGFβ3), in the absence and presence of IL-1β and exposed or unexposed to EMFs. Biochemical, quantitative real-time RT-PCR and histological results showed that EMFs alone or in the presence of TGFβ3 play a limited role in promoting chondrogenic differentiation. Notably, in the presence of IL-1β and TGFβ3 a recovery of proteoglycan (PG) synthesis, PG content and aggrecan and type II collagen mRNA expression in the EMF-exposed compared to unexposed pellets was observed. Also, histological and immunohistochemical results showed an increase in staining for alcian blue, type II collagen and aggrecan in EMF-exposed pellets. In conclusion, this study shows a significant role of EMFs in counteracting the IL-1β-induced inhibition of chondrogenesis, suggesting EMFs as a therapeutic strategy for improving the clinical outcome of cartilage engineering repair procedures, based on the use of MSCs.

Downregulation of A(1) and A(2B) adenosine receptors in human trisomy 21 mesenchymal cells from first-trimester chorionic villi

Human reproduction is complex and prone to failure. Though causes of miscarriage remain unclear, adenosine, a proangiogenic nucleoside, may help determine pregnancy outcome. Although adenosine receptor (AR) expression has been characterized in euploid pregnancies, no information is available for aneuploidies, which, as prone to spontaneous abortion (SA), are a potential model for shedding light on the mechanism regulating this event. AR expression was investigated in 71 first-trimester chorionic villi (CV) samples and cultured mesenchymal cells (MC) from euploid and TR21 pregnancies, one of the most frequent autosomal aneuploidy, with a view to elucidating their potential role in the modulation of vascular endothelial growth factor (VEGF) and nitric oxide (NO). Compared to euploid cells, reduced A(1) and A(2B) expression was revealed in TR21 CV and MCs. The non-selective adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA) increased NO, by activating, predominantly, A(1)AR and A(2A)AR through a molecular pathway involving hypoxia-inducible-factor-1 (HIF-1α), and increased VEGF, mainly through A(2B). In conclusion the adenosine transduction cascade appears to be disturbed in TR21 through reduced expression of A(2B) and A(1)ARs. These anomalies may be implicated in complications such as fetal growth restriction, malformation and/or SA, well known features of aneuploid pregnancies. Therefore A(1) and A(2B)ARs could be potential biomarkers able to provide an early indication of SA risk and their stimulation may turn out to improve fetoplacental perfusion by increasing NO and VEGF.

The stimulation of A(3) adenosine receptors reduces bone-residing breast cancer in a rat preclinical model

Amongst cancers with poor prognosis those originating from breast commonly metastasise to the skeleton for the high affinity of breast cancer cells to bone. A(3) adenosine receptor (A(3)AR) agonists were found to be potent anti-tumour agents even if their effect on bone-residing breast cancer has not yet been investigated. An animal model of surgery-induced metastasis was used to mimic the human condition in an attempt to develop a novel effective treatment strategy. Sprague-Dawley rats receiving intra-tibial injections of syngeneic MRMT-1 rat mammary gland carcinoma cells developed cancer-associated osteolytic lesions and structural damage that were monitored by microcomputed tomography imaging and histological analysis. To address the involvement of A(3)ARs in tumour-related signalling pathway, A(3)AR expression and functional role were analysed in MRMT-1 cells. The effect of chronic treatment with an A(3)AR agonist, 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyl-uronamide (Cl-IB-MECA) in comparison with cisplatin, was evaluated on rat tumour growth and bone cancer pain. A(3)ARs were expressed in MRMT-1 cells and their activation reduced NF-kB, increased p53 expression and apoptosis, inhibited tumour cell proliferation and migration. In vivo Cl-IB-MECA administration, started on day 1 after tumour cell injection, produced a significant reduction in tumour growth and cancer pain. Cl-IB-MECA treatment, performed on days 5 and 10 after the tumour cell inoculation, revealed the capability of A(3)AR stimulation to partially reduce tumour progression. Our findings highlighted the effectiveness of A(3)AR stimulation in the inhibition of breast tumour-derived bone metastasis growth strongly suggesting that targeting A(3)ARs may have promising therapeutic value in the treatment of bone-residing breast cancer.