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B N Cronstein

Publications and source records attributed to B N Cronstein.

At least 37 records · Page 2Linked to original sources
PubMed1996

TSG-6, a glycoprotein associated with arthritis, and its ligand hyaluronan exert opposite effects in a murine model of inflammation.

TSG-6 is an arthritis-associated hyaluronan binding protein whose production in synovial cells, chondrocytes, fibroblasts and mononuclear cells is stimulated by TNF-alpha and IL-1. The purpose of this study was to gain insights into the role of TSG-6 and its functional interactions with hyaluronan in inflammation. In the murine air pouch model of carrageenan/IL-1-induced inflammation TSG-6 showed a dramatic inhibitory effect on the cellular infiltration of the inflammatory site by neutrophilic PMN, while hyaluronan enhanced cellular infiltration. There was no indication of a neutralizing or cooperative effect when TSG-6 and hyaluronan were injected together. The potent antiinflammatory effect of TSG-6 along with its induction by proinflammatory cytokines suggests that TSG-6 is part of a negative feedback loop in the control of the inflammatory response.

Animals↗
PubMed1995

Identification of C1q as the heat-labile serum cofactor required for immune complexes to stimulate endothelial expression of the adhesion molecules E-selectin and intercellular and vascular cell adhesion molecules 1.

To examine the role of complement components as regulators of the expression of endothelial adhesive molecules in response to immune complexes (ICs), we determined whether ICs stimulate both endothelial adhesiveness for leukocytes and expression of E-selectin and intercellular and vascular cell adhesion molecules 1 (ICAM-1 and VCAM-1). We found that ICs [bovine serum albumin (BSA)-anti-BSA] stimulated endothelial cell adhesiveness for added leukocytes in the presence of complement-sufficient normal human serum (NHS) but not in the presence of heat-inactivated serum (HIS) or in tissue culture medium alone. Depletion of complement component C3 or C8 from serum did not prevent enhanced endothelial adhesiveness stimulated by ICs. In contrast, depletion of complement component C1q markedly inhibited IC-stimulated endothelial adhesiveness for leukocytes. When the heat-labile complement component C1q was added to HIS, the capacity of ICs to stimulate endothelial adhesiveness for leukocytes was completely restored. Further evidence for the possible role of C1q in mediating the effect of ICs on endothelial cells was the discovery of the presence of the 100- to 126-kDa C1q-binding protein on the surface of endothelial cells (by cytofluorography) and of message for the 33-kDa C1q receptor in resting endothelial cells (by reverse transcription-PCR). Inhibition of protein synthesis by cycloheximide blocked endothelial adhesiveness for leukocytes stimulated by either interleukin 1 or ICs in the presence of NHS. After stimulation with ICs in the presence of NHS, endothelial cells expressed increased numbers of adhesion molecules (E-selectin, ICAM-1, and VCAM-1). Endothelial expression of adhesion molecules mediated, at least in part, endothelial adhesiveness for leukocytes, since leukocyte adhesion was blocked by monoclonal antibodies directed against E-selectin. These studies show that ICs stimulate endothelial cells to express adhesive proteins for leukocytes in the presence of a heat-labile serum factor. That factor appears to be C1q.

Antigen-Antibody Complex↗
PubMed1995

The antiinflammatory effects of an adenosine kinase inhibitor are mediated by adenosine.

OBJECTIVE: The acute antiinflammatory effects of methotrexate are mediated, at least in part, by increased extracellular adenosine concentrations at inflamed sites. This observation suggests that other agents that increase extracellular adenosine concentrations might also reduce inflammation. Since adenosine can be rapidly taken up by cells, phosphorylated by adenosine kinase, and maintained intracellularly as adenine nucleotides, we investigated whether a potent inhibitor of adenosine kinase, GP-1-515, could increase exudate adenosine concentration and thereby diminish inflammation in the murine air pouch model of inflammation. METHODS: We studied the effect of various oral doses of GP-1-515 on carrageenan-induced inflammation in air pouches induced on BALB/c mice. Adenosine concentration in pouch exudates was determined by high performance liquid chromatography, and intensity of inflammation was determined by leukocyte counts in the exudate fluid. RESULTS: There was a greater concentration of adenosine in the pouch exudates of animals treated with GP-1-515 than of those treated with saline (P < 0.002). GP-1-515 inhibited, in a dose-dependent manner (P < 0.01), leukocyte accumulation in the murine air pouch in response to carrageenan. Inhibition of inflammation by GP-1-515 in this model depended upon increased adenosine concentration in the inflamed pouch since injection of adenosine deaminase into the air pouch with the carrageenan completely reversed the antiinflammatory effects of GP-1-515 at all doses of GP-1-515 tested. Moreover, as previously demonstrated, the antiinflammatory effects of adenosine were mediated via occupancy of adenosine A2 receptors, since the specific adenosine A2 receptor antagonist 3,7-dimethyl-1-propargylxanthine, but not the A1 receptor antagonist 8-cyclopentyl-dipropylxanthine, completely reversed the antiinflammatory effects of GP-1-515. GP-1-515 also decreased tumor necrosis factor alpha levels in the air pouch exudates by 51%, most likely as a result of the direct action of adenosine on macrophages. CONCLUSION: These results indicate that the antiinflammatory actions of GP-1-515 are mediated by adenosine. The development of agents that promote adenosine release at sites of inflammation is a novel strategy for the treatment of inflammatory diseases such as rheumatoid arthritis.

Adenosine↗
PubMed1995

Targets for antiinflammatory drugs.

Aspirin-like nonsteroidal antiinflammatory agents, corticosteroids, and methotrexate are the mainstays of therapy in rheumatoid arthritis and other inflammatory diseases. It is now clear that these agents share at least one characteristic: All of these agents diminish the adhesive interactions required for the accumulation of white blood cells at an inflamed site. We discuss the biochemical and functional mechanisms by which these drugs alter the inflammatory response, and the potential for development of new antiinflammatory agents based upon these pharmacological actions.

Adrenal Cortex Hormones↗
PubMed1995

Colchicine alters the quantitative and qualitative display of selectins on endothelial cells and neutrophils.

Since colchicine-sensitive microtubules regulate the expression and topography of surface glycoproteins on a variety of cells, we sought evidence that colchicine interferes with neutrophil-endothelial interactions by altering the number and/or distribution of selectins on endothelial cells and neutrophils. Extremely low, prophylactic, concentrations of colchicine (IC50 = 3 nM) eliminated the E-selectin-mediated increment in endothelial adhesiveness for neutrophils in response to IL-1 (P < 0.001) or TNF alpha (P < 0.001) by changing the distribution, but not the number, of E-selectin molecules on the surface of the endothelial cells. Colchicine inhibited stimulated endothelial adhesiveness via its effects on microtubules since vinblastine, an agent which perturbs microtubule function by other mechanisms, diminished adhesiveness whereas the photoinactivated colchicine derivative gamma-lumicolchicine was inactive. Colchicine had no effect on cell viability. At higher, therapeutic, concentrations colchicine (IC50 = 300 nM, P < 0.001) also diminished the expression of L-selectin on the surface of neutrophils (but not lymphocytes) without affecting expression of the beta 2-integrin CD11b/CD18. In confirmation, L-selectin expression was strikingly reduced (relative to CD11b/CD18 expression) on neutrophils from two individuals who had ingested therapeutic doses of colchicine. These results suggest that colchicine may exert its prophylactic effects on cytokine-provoked inflammation by diminishing the qualitative expression of E-selectin on endothelium, and its therapeutic effects by diminishing the quantitative expression of L-selectin on neutrophils.

Animals↗
PubMed1995

The antirheumatic agents sulphasalazine and methotrexate share an anti-inflammatory mechanism.

Increasingly, methotrexate (MTX) and sulphasalazine (SASP) are used initially for second-line therapy of rheumatoid arthritis (RA). Although SASP and MTX are commonly used, the mechanism(s) by which these drugs control the inflammation that characterizes RA have remained obscure. Results from my laboratory indicate that these agents share a mode of action; the anti-inflammatory effects of both SASP and MTX are due, in both in vitro and in vivo studies, to their capacity to enhance adenosine release at inflamed sites. This mode of action suggests that the development of agents that directly alter adenosine metabolism may lead to new, more effective and safer antirheumatic drugs than those currently available.

Anti-Inflammatory Agents↗
PubMed1994

Immunocomplexes stimulate different signalling events to chemoattractants in the neutrophil and regulate L-selectin and beta 2-integrin expression differently.

Neutrophils express receptors for numerous phlogistons which, when occupied, trigger distinct signal-transduction pathways. Previous studies have shown that stimulation of neutrophils with chemoattractants induces shedding of the adhesive molecule L-selectin and increased expression of the beta 2-integrin CD11b/CD18. We determined the effect of ligation of classic, G-protein-linked chemoattractant receptors [C5a, interleukin-8 (IL-8), formylmethionyl-leucylphenylalanine (FMLP) and substance P], receptors for the Fc portion of IgG (Fc gamma receptors) and receptors for transforming growth factor beta (TGF beta) on expression of adhesive molecules by neutrophils and the stimulus-transduction mechanisms thought to mediate these changes. We were surprised to observe that occupancy of Fc gamma receptors by immunocomplexes (BSA-anti-BSA) stimulated increased expression by neutrophils of CD11b/CD18 at concentrations which did not affect L-selectin expression (EC50 9 micrograms/ml versus 350 micrograms/ml respectively, P < 0.00001, n = 5). In contrast, similar to previous studies, recombinant C5a, recombinant IL-8 and FMLP all stimulated increased expression of CD11b/CD18 (170-260% of basal, P < 0.001, n = 5) and shedding of L-selectin (56-75% reduction from basal, P < 0.001, n = 5) at similar concentrations and with similar potencies (EC50 = 2, 5, and 3 nM respectively). In contrast, neither TGF beta 1 nor, surprisingly, substance P affected expression of CD11b/CD18 or L-selectin. The regulation of expression of CD11b/CD18 or L-selectin in response to FMLP or immunocomplexes was unaffected by cytochalasin B (5 micrograms/ml) or the tyrosine kinase inhibitor tyrphostin-25 (25 microM). Although occupancy of both chemoattractant (FMLP) and Fc gamma receptors stimulated increments in the second messenger diacylglycerol, disruption of actin microfilaments by cytochalasin B enhanced diacylglycerol generation in response to FMLP but not in response to ligation of Fc gamma receptors. Moreover, both FMLP and immune aggregates provoked fluxes of intracellular Ca2+ concentration which differed with respect to both magnitude and kinetics and did not correlate well with regulation of adhesive-molecule expression. As upregulation of CD11b/CD18 is tightly linked to exocytosis of specific granules, these results suggest that shedding of L-selectin by activated neutrophils is not linked to exocytosis. These studies provide further evidence that receptors for chemoattractants and immunocomplexes on the neutrophil are linked to multiple signalling pathways.

Actins↗
PubMed1994

Neutrophil chemotaxis in response to TGF-beta isoforms (TGF-beta 1, TGF-beta 2, TGF-beta 3) is mediated by fibronectin.

TGF-beta isoforms regulate numerous cellular functions including cell growth and differentiation, the cellular synthesis and secretion of extracellular matrix proteins, such as fibronectin (Fn), and the immune response. We have previously shown that TGF-beta 1 is the most potent chemoattractant described for human peripheral blood neutrophils (PMNs), suggesting that TGF-beta s may play a role in the recruitment of PMNs during the initial phase of the inflammatory response. In our current studies, we demonstrate that the maximal chemotactic response was attained near 40 fM for all mammalian TGF-beta isoforms. However, there was a statistically significant difference in migratory distance of the PMNs: TGF-beta 2 (556 microM) > TGF-beta 3 (463 microM) > TGF-beta 1 (380 microM) (beta 2: beta 3, p < or = 0.010; beta 3: beta 1, p < or = 0.04; beta 2: beta 1, p < or = 0.0012). A mAb to the cell binding domain (CBD) of Fn inhibited the chemotactic response to TGF-beta 1 and TGF-beta 3 by 63% and to TGF-beta 2 by 70%, whereas the response to FMLP, a classic chemoattractant, was only inhibited by 18%. In contrast, a mAb to a C-terminal epitope of Fn did not retard migration (< 1.5%). The Arg-gly-Asp-ser tetrapeptide inhibited chemotaxis by approximately the same extent as the anti-CBD (52 to 83%). Furthermore, a mAb against the VLA-5 integrin (VLA-5; Fn receptor) also inhibited TGF-beta-induced chemotaxis. These results indicate that chemotaxis of PMNs in response to TGF-beta isoforms is mediated by the interaction of the Arg-gly-Asp-ser sequence in the CBD of Fn with an integrin on the PMN cell surface, primarily the VLA-5 integrin. TGF-beta isoforms also elicited the release of cellular Fn from PMNs; we observed a 2.3-fold increase in Fn (389 to 401 ng/ml) in the supernatants of TGF-beta-stimulated PMNs compared with unstimulated cells (173.6 ng/ml). The concentration of TGF-beta required to cause maximal release of Fn from PMNs (4000 fM) is a concentration at which TGF-beta is no longer chemotactic, suggesting that PMNs only use Fn that is constitutively expressed for migration. At higher concentrations of TGF-beta, the Fn released may accumulate basal to the cell, ultimately retarding cellular migration and modulating the chemotactic response.

Amino Acid Sequence↗
PubMed1994

Intravascular neutrophil activation in systemic lupus erythematosus (SLE): dissociation between increased expression of CD11b/CD18 and diminished expression of L-selectin on neutrophils from patients with active SLE.

Previous studies have shown that neutrophils in the circulation of patients with active systemic lupus erythematosus (SLE) are activated as judged by their increased surface expression of the beta 2-integrin CD11b/CD18. Since activation of neutrophils leads to altered expression of another adhesion molecule, L-selectin (LS), we examined neutrophils from patients with SLE for changes in the expression of CD11b/CD18 and LS by cytofluorographic analysis of immunofluorescent-labeled cells. Overall there was no difference between surface expression of CD11b/CD18 on neutrophils from SLE patients or controls [mean fluorescence 225 +/- 26 vs 225 +/- 13 relative fluorescence units (RFU), respectively]. However, as previously reported, neutrophils from patients with more active disease (activity score > or = 3, UCH Middlesex activity score) expressed greater CD11b/CD18 than neutrophils from controls (319 +/- 40 RFU, P < 0.03, n = 9) or from patients with less active disease (193 +/- 10 RFU, P < 0.006). Indeed, CD11b/CD18 expression correlated directly with disease activity (r = 0.54, P < 0.02). Stimulation of neutrophils ex vivo with the chemoattractant N-formyl-methionyl-leucyl-phenylalanine (100 nM) induced up-regulation of CD11b/CD18 in cells from both SLE patients and controls (205 +/- 12% vs 239 +/- 15% of basal, respectively), but neutrophils from the most active patients (score > or = 3) increased CD11b/CD18 expression less than controls (175 +/- 12% of basal, P < 0.003, n = 9). The magnitude of the stimulated increment in expression of CD11b/CD18 on neutrophils correlated inversely with SLE activity (r = -0.64, P < 0.003, n = 20). Surprisingly, we observed no change in LS expression on neutrophils from SLE patients compared to controls (143 +/- 14 vs 141 +/- 16 RFU, respectively) even in patients with the highest activity indices (154 +/- 21 RFU). In contrast to CD11b/CD18, there was no correlation between LS expression and disease activity (r = 0.12, P = NS). Stimulation of neutrophils reduced the expression of LS similarly in both controls and SLE patients (67 +/- 3% vs 58 +/- 4% reduction, respectively) and did not correlate with disease activity (r = 0.07, P = NS, n = 20). These results show, for the first time, that changes in CD11b/CD18 expression do not correlate with LS expression on neutrophils from patients with active SLE.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigens, CD↗
PubMed1994

The antiinflammatory effects of methotrexate are mediated by adenosine.

In summary, intermittent, low dose methotrexate treatment is: 1.) antiinflammatory in the murine air pouch model of inflammation; 2.) selectively increases intracellular AICAR concentration; 3.) increases adenosine concentration in an inflammatory exudate; and, 4.) inhibits leukocyte accumulation at an inflamed site by a mechanism that is specifically reversed by adenosine deaminase and the adenosine A2 receptor antagonist DMPX but not the A1 antagonist DPCPX. In conclusion, we have demonstrated a novel mechanism for the antiinflammatory action of methotrexate; methotrexate is a nonsteroidal antiinflammatory agent that acts by promoting the release of adenosine which engages A2 receptors on inflammatory cells.

Acyltransferases↗
PubMed1994

Nonsteroidal antiinflammatory agents inhibit stimulated neutrophil adhesion to endothelium: adenosine dependent and independent mechanisms.

All nonsteroidal antiinflammatory drugs (NSAIDs) inhibit neutrophil aggregation (homotypic cell-cell adhesion) and do so without affecting expression of CD11b/CD18. Since the first step in acute inflammation is a critical interaction between neutrophils and the vascular endothelium (heterotypic cell-cell adhesion), we determined whether NSAIDs diminish the adherence of neutrophils to the endothelium. At antiinflammatory concentrations (0.5-5 mM) sodium salicylate, an NSAID that does not inhibit prostaglandin synthesis, inhibited stimulated but not unstimulated neutrophil adherence to endothelial cells (IC50 < 1 mM, P < 0.00001). Salicylates have previously been shown to inhibit oxidative phosphorylation and, predictably, sodium salicylate inhibited oxidative phosphorylation, as evidenced by depletion of ATP stores (875 +/- 75 pmol/10(6) PMN, [2.92 +/- 0.25 mM]) in stimulated (FMLP, 0.1 microM) but not resting neutrophils treated with antiinflammatory doses of sodium salicylate (EC50 = 1 mM, P < 0.00001). Indomethacin and piroxicam (10 and 30 microM) only minimally decreased ATP concentrations in stimulated and resting neutrophils. ATP is metabolized to adenosine, and we have previously demonstrated that both endogenously released (180-200 nM) and exogenous adenosine (IC50 = 250 nM) inhibit stimulated neutrophil adherence to endothelial cells. To determine whether the increased metabolism of ATP and the resultant increase in adenosine release were responsible for inhibition of neutrophil adhesion to endothelium, we determined whether addition of adenosine deaminase (ADA, 0.125 IU/ml), an enzyme that converts extracellular adenosine to its inactive metabolite, inosine, affected inhibition of neutrophil adhesion to endothelium by stimulated neutrophils. ADA significantly reversed inhibition of neutrophil adherence to endothelium by sodium salicylate (0.5-5 mM, P < 0.00001). This suggests that sodium salicylate inhibits neutrophil adherence by increasing adenosine release. Whereas indomethacin and piroxicam (10-50 microM) also inhibited stimulated neutrophil adherence to endothelial cells, ADA did not affect their inhibition of adherence. These studies demonstrate a heretofore unexpected antiinflammatory mechanism for salicylates: salicylates increase ATP hydrolysis and thereby enhance release of adenosine. Moreover, these data are consistent with the hypothesis that NSAIDs differ from one another with respect to their mechanisms of action.

Adenosine↗
PubMed1994

Adhesion molecules in the pathogenesis of rheumatoid arthritis.

The molecules on the cell surface that mediate inflammatory interactions between endothelial cells and leukocytes and of leukocytes with one another have been isolated and their fine structure elucidated. Early studies clearly indicated that the interactions mediated by these proteins are involved in the pathogenesis of rheumatoid arthritis. This article is a review of work published over the past year that has confirmed and expanded the role of adhesive proteins on vascular endothelium, leukocytes, and other synovial cells in the pathogenesis of rheumatoid arthritis. Moreover, the results of recent studies have suggested novel strategies for the development of agents for the treatment of rheumatoid arthritis.

Adrenal Cortex Hormones↗
PubMed1994

Adenosine, an endogenous anti-inflammatory agent.

Adenosine receptors are present on most cells and organs, yet, although the physiological effects of adenosine were first described over 60 years ago, the potential therapeutic uses of adenosine have only been recognized and realized recently. A decade ago the potent anti-inflammatory effects of adenosine were first described; adenosine, acting at specific A2 receptors, inhibits some, but not all, neutrophil functions. Adenosine inhibits phagocytosis, generation of toxic oxygen metabolites, and adhesion (to some surfaces and to endothelial cells) but does not inhibit degranulation or chemotaxis. Occupancy of adenosine A2 receptors modulates leukocyte function by a novel mechanism. Although adenosine A2 receptors are classically linked to heterotrimeric GS signaling proteins and stimulation of adenylate cyclase, adenosine 3',5'-cyclic monophosphate does not act as the second messenger for inhibition of leukocyte function. By a mechanism that still remains obscure, occupancy of adenosine A2 receptors on neutrophils "uncouples" chemoattractant receptors from their stimulus-transduction proteins. The concentrations of adenosine that inhibit inflammatory cell function are similar to those observed in vivo and suggest a role for adenosine in the modulation of inflammation in vivo. Indeed, recent studies indicate that nonmetabolized adenosine receptor agonists are potent anti-inflammatory agents, and other studies indicate that methotrexate, a commonly used anti-inflammatory agent, diminishes inflammation by increasing adenosine release at inflamed sites. The observations reviewed here suggest that adenosine and agents that act through adenosine are excellent candidates for development as anti-inflammatory agents.

Adenosine↗
PubMed1993

Chemoattraction of neutrophils by substance P and transforming growth factor-beta 1 is inadequately explained by current models of lipid remodeling.

"Classical" chemoattractants, such as FMLP, C5a, or leukotriene B4, not only elicit directed motility but also activate neutrophils (degranulation, release of active oxygen species). Signal transduction after ligation of receptors for these classical chemoattractants is mediated by pertussis toxin (PT)-sensitive, heterotrimeric G proteins and the early production of lipid messengers via phospholipases. In contrast, we have previously shown that substance P (SP) and transforming growth factor-beta 1 (TGF-beta 1) are "pure" chemoattractants in that they elicit chemotaxis without activating neutrophils. Paradoxically, pure chemoattractants also activate G proteins (plasmalemmal GTPase activity) without eliciting increments in cytosolic calcium ([Ca]i) and thus inositol trisphosphate. We therefore determined lipid remodeling and signal transduction in response to pure chemoattractants. Increments in plasmalemmal GTPase activated by SP (0.1 microM) and TGF-beta 1 (40 fM), like that after FMLP, were PT-sensitive (SP = 6.6 +/- 2 pm/mg/min vs SP + PT = 1.1 +/- 0.9 over basal activity; TGF-beta 1 = 4.3 +/- 1.6 vs TGF-beta 1 + PT = 2.3 +/- 0.9). In parallel, treatment of PMN with PT (1 microgram/ml, 30 min) inhibited chemotaxis (under agarose) after FMLP (2175 +/- 176 (SEM) microns vs 726 +/- 267) and SP (411 +/- 99 microns vs 103 +/- 62 microns) and TGF-beta 1 (40 fM, 375 +/- 53 microns vs 83 +/- 47). However, G proteins coupled to receptors for SP and TGF-beta 1, unlike FMLP, did not appear to be linked to phospholipases in that neither increments in diacylglycerol were detected after receptor ligation (FMLP = 152 +/- 22% resting levels; SP = 101 +/- 5%; TGF-beta 1 = 105 +/- 4%) nor was alkylacylglycerol increased by exposure to SP or TGF-beta 1 (SP = 92 +/- 4%; TGF-beta 1 = 101 +/- 8%; FMLP = 226 +/- 40%). Moreover, polymorphonuclear leukocytes failed to generate phosphatidates (PA) of either species after SP (DA-PA = 79 +/- 9% resting at 60 s; EA-PA = 103 +/- 4%) or TGF-beta 1 (DA-PA = 101 +/- 5%; EA-PA = 98 +/- 9%) in contrast to FMLP (DA-PA = 155 +/- 22%; EA-PA = 149 +/- 16%). The data clearly contravene the current dogma that all chemoattractants use inositol trisphosphate and diglycerides as intracellular signals and suggest the presence of a unique subset of PT-sensitive G proteins, not coupled to "classical" phospholipases, transduce chemoattraction.

Adult↗
PubMed1993

The antiinflammatory mechanism of methotrexate. Increased adenosine release at inflamed sites diminishes leukocyte accumulation in an in vivo model of inflammation.

Methotrexate, a folate antagonist, is a potent antiinflammatory agent when used weekly in low concentrations. We examined the hypothesis that the antiphlogistic effects of methotrexate result from its capacity to promote intracellular accumulation of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) that, under conditions of cell injury, increases local adenosine release. We now present the first evidence to establish this mechanism of action in an in vivo model of inflammation, the murine air pouch model. Mice were injected intraperitoneally with either methotrexate or saline for 3-4 wk during induction of air pouches. Pharmacologically relevant doses of methotrexate increased splenocyte AICAR content, raised adenosine concentrations in exudates from carrageenan-inflamed air pouches, and markedly inhibited leukocyte accumulation in inflamed air pouches. The methotrexate-mediated reduction in leukocyte accumulation was partially reversed by injection of adenosine deaminase (ADA) into the air pouch, completely reversed by a specific adenosine A2 receptor antagonist, 3,7-dimethyl-1-propargylxanthine (DMPX), but not affected by an adenosine A1 receptor antagonist, 8-cyclopentyl-dipropylxanthine. Neither ADA nor DMPX affected leukocyte accumulation in the inflamed pouches of animals treated with either saline or the potent antiinflammatory steroid dexamethasone. These results indicate that methotrexate is a nonsteroidal antiinflammatory agent, the antiphlogistic action of which is due to increased adenosine release at inflamed sites.

Adenosine↗