Methotrexate remains a cornerstone in the treatment of rheumatoid arthritis and other rheumatic diseases. Folate antagonism is known to contribute to the antiproliferative effects that are important in the action of methotrexate against malignant diseases, but concomitant administration of folic or folinic acid does not diminish the anti-inflammatory potential of this agent, which suggests that other mechanisms of action might be operative. Although no single mechanism is sufficient to account for all the anti-inflammatory activities of methotrexate, the release of adenosine from cells has been demonstrated both in vitro and in vivo. Methotrexate might also confer anti-inflammatory properties through the inhibition of polyamines. The biological effects on inflammation associated with adenosine release have provided insight into how methotrexate exerts its effects against inflammatory diseases and at the same time causes some of its well-known adverse effects. These activities contribute to the complex and multifaceted mechanisms that make methotrexate efficacious in the treatment of inflammatory disorders.
"The earliest concept, borrowed from oncology applications, was that of anti-proliferative actions, thereby reducing the burden of inflammatory cells . Other potential mechanisms have been proposed, including interactions with adenosine signaling pathways and generation of ROS [8,19,20]. In previous studies we have shown that MTX primes T cells for apoptosis, an action that is dependent on JNK signaling pathways . "
[Show abstract][Hide abstract] ABSTRACT: Methotrexate (MTX) has been for decades a standard treatment in a wide range of conditions, from malignancies to rheumatoid arthritis (RA). Despite this long experience, mechanisms of action of MTX remain incompletely understood. Reported immunologic effects of MTX include induction of increased production of some cytokines, an effect that seems to be at odds with the generally anti-inflammatory effects of this drug in diseases like RA. To further elucidate these immune activities, we examined effects of MTX on the human monocytic cell line U937.
The U937 cell line was treated in vitro with pharmacologic range concentrations of MTX and effects on production of interleukin (IL)-1, IL-6 and TNF alpha were measured. Changes in gene expression for IL-1 and IL-6 and specificities in the Jun-N-terminal kinase (JNK) signaling pathway including JNK 1, JNK2, JUN and FOS were also determined. The contribution of NFkB, folate and adenosine pathways to the observed effects were determined by adding appropriate inhibitors to the MTX cultures.
MTX mediated a dose-dependent increase in IL-1 and IL-6 in U937 cells, as measured by secreted proteins and levels of gene expression. The increased cytokine expression was inhibited by addition of parthenolide and folinic acid, but not by caffeine and theophylline, suggesting that NFkB and folates, but not adenosine, were involved in mediating the observed effects. When U937 cells were cultured with MTX, upregulated expression of JUN and FOS, but not JNK 1 or 2, also was observed.
MTX induces expression of pro-inflammatory cytokines in U937 monocytic cells. These effects might mediate the known toxicities of MTX including pneumonitis, mucositis and decreased bone mineral density.
"To this end, how do we reconcile these findings? Affirming the diverse effects of MTX on the immune system , MTX has previously been shown to act as a strong differentiation factor for immature and undifferentiated monocytic cells in vitro
. With our treatment regimen, while MTX alone did not trigger monocyte elevation in vivo, likely due to the low dosage of MTX administered, in the presence of RRV infection, MTX treatment boosts systemic monocyte generation. "
[Show abstract][Hide abstract] ABSTRACT: Part of the Togaviridae family, alphaviruses, including chikungunya virus (CHIKV), Sindbis virus (SINV) and Ross River virus (RRV), are able to cause significant inflammatory pathologies ranging from arthritis to encephalitis. Following symptomatic infection with arthritis-associated alphaviruses, patients often experience severe joint pain, affecting distal and small joints, which can last six months or longer. Recently, methotrexate (MTX), a disease modifying anti-rheumatic drug (DMARD), was used to treat patients experiencing chronic rheumatic symptoms following infection with CHIKV. Here, the effect of MTX on Ross River virus disease (RRVD) in mice was examined to better understand its therapeutic potential for alphaviral-induced musculoskeletal disease and to further our knowledge of the development of alphaviral pathologies. Using a mouse model, we analyzed the effect of MTX on RRVD. RRV disease pathogenesis in response to MTX treatment was determined by measuring levels of proinflammatory factors, cellular infiltrates, viral titer and histological analysis of infected tissues. RRV-infected mice receiving MTX treatment rapidly developed musculoskeletal disease, which correlated with a significant influx of inflammatory cell infiltrates into the skeletal muscle tissue. Although no difference was observed in the level of proinflammatory cytokines and chemokines, the viral load increased at early time points post infection in the serum and quadriceps of MTX treated mice, possibly contributing to disease pathogenesis. Results suggest that MTX treatment of acute RRVD in mice provides no therapeutic benefit and underline the importance of inflammatory monocytes in alphaviral induced arthritides.
PLoS ONE 08/2013; 8(8):e71146. DOI:10.1371/journal.pone.0071146 · 3.23 Impact Factor
"Previously, we have reported that A2A receptors inhibit M-CSF/RANKL-stimulated osteoclast differentiation and function (Mediero et al., 2012b) and the selective A2AR agonist CGS21680 reduced in vivo wear particle-induced bone pitting and porosity, increasing cortical bone and bone volume compared to control mice (Mediero et al., 2012a). Similarly, methotrexate, the gold standard drug in the treatment of rheumatoid arthritis, mediates many of its anti-inflammatory effects by increasing release of adenosine which stimulates A2A and A3 receptors to diminish inflammation and bony erosions (Chan and Cronstein, 2010). To better understand the role of adenosine and its receptors in the suppression of inflammatory bone resorption, we determined which intracellular pathways are involved in A2AR-mediated regulation of osteoclast differentiation. "
[Show abstract][Hide abstract] ABSTRACT: Background and purpose:
We previously reported that adenosine, acting at adenosine A(2A) receptors (A(2A)R), inhibits osteoclast (OC) differentiation in vitro (A(2A)R activation OC formation reduces by half) and in vivo. For a better understanding how adenosine A(2A)R stimulation regulates OC differentiation, we dissected the signalling pathways involved in A(2A)R signalling.
OC differentiation was studied as TRAP+ multinucleated cells following M-CSF/RANKL stimulation of either primary murine bone marrow cells or the murine macrophage line, RAW264.7, in presence/absence of the A(2A)R agonist CGS21680, the A(2A)R antagonist ZM241385, PKA activators (8-Cl-cAMP 100 nM, 6-Bnz-cAMP) and the PKA inhibitor (PKI). cAMP was quantitated by EIA and PKA activity assays were carried out. Signalling events were studied in PKA knockdown (lentiviral shRNA for PKA) RAW264.7 cells (scrambled shRNA as control). OC marker expression was studied by RT-PCR.
A(2A)R stimulation increased cAMP and PKA activity which and were reversed by addition of ZM241385. The direct PKA stimuli 8-Cl-cAMP and 6-Bnz-cAMP inhibited OC maturation whereas PKI increased OC differentiation. A(2A)R stimulation inhibited p50/p105 NFκB nuclear translocation in control but not in PKA KO cells. A(2A)R stimulation activated ERK1/2 by a PKA-dependent mechanism, an effect reversed by ZM241385, but not p38 and JNK activation. A(2A)R stimulation inhibited OC expression of differentiation markers by a PKA-mechanism.
Conclusions and implications:
A(2A)R activation inhibits OC differentiation and regulates bone turnover via PKA-dependent inhibition of NFκB nuclear translocation, suggesting a mechanism by which adenosine could target bone destruction in inflammatory diseases like rheumatoid arthritis.
British Journal of Pharmacology 05/2013; 169(6). DOI:10.1111/bph.12227 · 4.84 Impact Factor
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