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1.
Adenosine and its metabolite, inosine, have been described as molecules that participate in regulation of inflammatory response. The aim of this study was to investigate the effect of adenosine and inosine in a mouse model of carrageenan-induced pleurisy as well as the participation of adenosine receptors in this response. Injection of carrageenan into the pleural cavity induced an acute inflammatory response characterized by leukocyte migration, pleural exudation, and increased release of interleukin-1β and tumor necrosis factor-α in pleural exudates. The treatment with adenosine (0.3–100 mg/kg, i.p.) and inosine (0.1–300 mg/kg, i.p.) 30 min before carrageenan injection reduced significantly all these parameters analyzed. Our results also demonstrated that A 2A and A 2B receptors seem to mediate the adenosine and inosine effects observed, since pretreatment with selective antagonists of adenosine A 2A (ZM241385) and A 2B (alloxazine) receptors, reverted the inhibitory effects of adenosine and inosine in pleural inflammation. The involvement of A 2 receptors was reinforced with adenosine receptor agonist {"type":"entrez-protein","attrs":{"text":"CGS21680","term_id":"878113053","term_text":"CGS21680"}}CGS21680 treatment, since its anti-inflammatory effects were reversed completely and partially with ZM241385 and alloxazine injection, respectively. Moreover, the combined treatment with subeffective dose of adenosine (0.3 mg/kg) and inosine (1.0 mg/kg) induced a synergistic anti-inflammatory effect. Thus, based on these findings, we propose that inosine contributes with adenosine to exert anti-inflammatory effects in pleural inflammation, reinforcing the notion that endogenous nucleosides play an important role in controlling inflammatory diseases. This effect is likely mediated by the activation of adenosine A 2 subtype receptors and inhibition of production or release of pro-inflammatory cytokines. 相似文献
2.
This study aimed to evaluate the role for adenosine A2A receptors in the autoregulatory vasodilation to hypotension in relation with cerebral blood flow (CBF) autoregulation in rat pial arteries. Changes in pial artery diameters were observed directly through a closed cranial window. Vasodilation induced by adenosine was markedly suppressed by ZM 241385 (1 micromol/l, A2A antagonist) and alloxazine (1 micromol/l, A2B antagonist), but not by 8-cyclopentyltheophylline (CPT, 1 micromol/l, A1 antagonist). CGS-21680-induced vasodilation was more strongly inhibited by ZM 241385 (25.3-fold; P<0.05) than by alloxazine. In contrast, 5'-N-ethylcarboxamido-adenosine (NECA)-induced vasodilation was more prominently suppressed by alloxazine (12.0-fold; P<0.001) than by ZM 241385. The autoregulatory vasodilation in response to acute hypotension of the pial arteries was significantly suppressed by ZM 241385, but not by CPT and alloxazine. Consistent with this finding, the lower limit of CBF autoregulation significantly shifted to a higher blood pressure by 1 micromol/l of ZM 241385 (53.0+/-3.9 mm Hg to 69.2+/-2.9 mm Hg, P<0.01) and 10 micromol/l of glibenclamide (54.7+/-6.5 mm Hg to 77.9+/-4.2 mm Hg, P<0.001), but not by CPT and alloxazine. Thus, it is suggested that adenosine-induced vasodilation of the rat pial artery is mediated via activation of adenosine A2A and A2B receptors, but not by A1 subtype, and activation of adenosine A2A receptor preferentially contributes to the autoregulatory vasodilation via activation of ATP-sensitive K+ channels in response to hypotension and maintenance of CBF autoregulation. 相似文献
3.
Little is known about the mechanisms that regulate the expression of adenosine receptors during CNS development. We demonstrate here that retinas from chick embryos injected in ovo with selective adenosine receptor ligands show changes in A1 receptor expression after 48 h. Exposure to A1 agonist N 6‐cyclohexyladenosine (CHA) or antagonist 8‐Cyclopentyl‐1, 3‐dipropylxanthine (DPCPX) reduced or increased, respectively, A1 receptor protein and [ 3H]DPCPX binding, but together, CHA+DPCPX had no effect. Interestingly, treatment with A 2A agonist 3‐[4‐[2‐[[6‐amino‐9‐[(2R,3R,4S,5S)‐5‐(ethylcarbamoyl)‐3,4‐dihydroxy‐oxolan‐2‐yl]purin‐2‐yl]amino] ethyl]phenyl] propanoic acid (CGS21680) increased A1 receptor protein and [ 3H]DPCPX binding, and reduced A 2A receptors. The A 2A antagonists 7‐(2‐phenylethyl)‐5‐amino‐2‐(2‐furyl)‐pyrazolo‐[4,3‐e]‐1,2,4‐trizolo[1,5‐c] pyrimidine (SCH58261) and 4‐(2‐[7‐amino‐2‐[2‐furyl][1,2,4]triazolo[2,3‐a][1,3,5]triazo‐5‐yl‐amino]ethyl)phenol (ZM241385) had opposite effects on A1 receptor expression. Exposure to CGS21680 + CHA did not change A1 receptor levels, whereas CHA + ZM241385 or CGS21680 + DPCPX had no synergic effect. The blockade of adenosine transporter with S‐(4‐nitrobenzyl)‐6‐thioinosine (NBMPR) also reduced [ 3H]DPCPX binding, an effect blocked by DPCPX, but not enhanced by ZM241385. [ 3H]DPCPX binding kinetics showed that treatment with CHA reduced and CGS21680 increased the Bmax, but did not affect Kd values. CHA, DPCPX, CGS21680, and ZM241385 had no effect on A1 receptor mRNA. These data demonstrated an in vivo regulation of A1 receptor expression by endogenous adenosine or long‐term treatment with A1 and A 2A receptors modulators. 相似文献
4.
Animal models of asthma have shown that limonene, a naturally occurring terpene in citrus fruits, can reduce inflammation and airway reactivity. However, the mechanism of these effects is unknown. We first performed computational and molecular docking analyses that showed limonene could bind to both A2A and A2B receptors. The pharmacological studies were carried out with A2A adenosine receptor knock-out (A2AKO) and wild-type (WT) mice using ovalbumin (OVA) to generate the asthma phenotype. We investigated the effects of limonene on lung inflammation and airway responsiveness to methacholine (MCh) and NECA (nonselective adenosine analog) by administering limonene as an inhalation prior to OVA aerosol challenges in one group of allergic mice for both WT and KO. In whole-body plethysmography studies, we observed that airway responsiveness to MCh in WT SEN group was significantly lowered upon limonene treatment but no effect was observed in A2AKO. Limonene also attenuated NECA-induced airway responsiveness in WT allergic mice with no effect being observed in A2AKO groups. Differential BAL analysis showed that limonene reduced levels of eosinophils in allergic WT mice but not in A2AKO. However, limonene reduced neutrophils in sensitized A2AKO mice, suggesting that it may activate A2B receptors as well. These data indicate that limonene-induced reduction in airway inflammation and airway reactivity occurs mainly via activation of A2AAR but A2B receptors may also play a supporting role. 相似文献
5.
Adenosine plays a dual role on acetylcholine (ACh) release from myenteric motoneurons via the activation of high-affinity inhibitory A 1 and facilitatory A 2A receptors. The therapeutic potential of adenosine-related compounds for controlling intestinal motility and inflammation, prompted us to investigate further the role of low-affinity adenosine receptors, A 2B and A 3, on electrically-evoked (5 Hz, 200 pulses) [ 3H]ACh release from myenteric neurons. Immunolocalization studies showed that A 2B receptors exhibit a pattern of distribution similar to the glial cell marker, GFAP. Regarding A 1 and A 3 receptors, they are mainly distributed to cell bodies of ganglionic myenteric neurons, whereas A 2A receptors are localized predominantly on cholinergic nerve terminals. Using selective antagonists (DPCPX, ZM241385 and MRS1191), data indicate that modulation of evoked [ 3H]ACh release is balanced through tonic activation of inhibitory (A 1) and facilitatory (A 2A and A 3) receptors by endogenous adenosine. The selective A 2B receptor antagonist, PSB603, alone was devoid of effect and failed to modify the inhibitory effect of NECA. The A 3 receptor agonist, 2-Cl-IB MECA (1–10 nM), concentration-dependently increased the release of [ 3H]ACh. The effect of 2-Cl-IB MECA was attenuated by MRS1191 and by ZM241385, which selectively block respectively A 3 and A 2A receptors. In contrast to 2-Cl-IB MECA, activation of A 2A receptors with CGS21680C attenuated nicotinic facilitation of ACh release induced by focal depolarization of myenteric nerve terminals in the presence of tetrodotoxin. Tandem localization of excitatory A 3 and A 2A receptors along myenteric neurons explains why stimulation of A 3 receptors (with 2-Cl-IB MECA) on nerve cell bodies acts cooperatively with prejunctional facilitatory A 2A receptors to up-regulate acetylcholine release. The results presented herein consolidate and expand the current understanding of adenosine receptor distribution and function in the myenteric plexus of the rat ileum, and should be taken into consideration for data interpretation regarding the pathophysiological implications of adenosine on intestinal motility disorders. 相似文献
6.
The aim of the present paper was to examine, in a comparative way, the occurrence and the mechanisms of the interactions between adenosine A 2A receptors (A 2ARs) and metabotropic glutamate 5 receptors (mGlu5Rs) in the hippocampus and the striatum. In rat hippocampal and corticostriatal slices, combined ineffective doses of the mGlu5R agonist 2-chloro-5-hydroxyphenylglycine (CHPG) and the A 2AR agonist CGS 21680 synergistically reduced the slope of excitatory postsynaptic field potentials (fEPSPs) recorded in CA1 and the amplitude of field potentials (FPs) recorded in the dorsomedial striatum. The cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway appeared to be involved in the effects of CGS 21680 in corticostriatal but not in hippocampal slices. In both areas, a postsynaptic locus of interaction appeared more likely. N-methyl- D-aspartate (NMDA) reduced the fEPSP slope and FP amplitude in hippocampal and corticostriatal slices, respectively. Such an effect was significantly potentiated by CHPG in both areas. Interestingly, the A 2AR antagonist ZM 241385 significantly reduced the NMDA-potentiating effect of CHPG. In primary cultures of rat hippocampal and striatal neurons (ED 17, DIV 14), CHPG significantly potentiated NMDA-induced lactate dehydrogenase (LDH) release. Again, such an effect was prevented by ZM 241385. Our results show that A 2A and mGlu5 receptors functionally interact both in the hippocampus and in the striatum, even though different mechanisms seem to be involved in the two areas. The ability of A 2ARs to control mGlu5R-dependent effects may thus be a general feature of A 2ARs in different brain regions (irrespective of their density) and may represent an additional target for the development of therapeutic strategies against neurological disorders. 相似文献
7.
Summary. Glutamate increases the extracellular adenosine levels, an important endogenous neuromodulator. The neurotoxicity induced
by glutamate increases the ecto-5′-nucleotidase activity in neurons, which produces adenosine from AMP. L- and D-aspartate
(Asp) mimic most of the actions of glutamate in the N-methyl-D-aspartate (NMDA) receptors. In the present study, both amino
acids stimulated the ecto-5′-nucleotidase activity in cerebellar granule cells. MK-801 and AP-5 prevented the L- and D-Asp-evoked
activation of ecto-5′-nucleotidase. Both NMDA receptor antagonists prevented completely the damage induced by L-Asp, but partially
the D-Asp-induced damage. The antagonist of adenosine A 2A receptors (ZM 241385) prevented totally the L- Asp-induced cellular death, but partially the neurotoxicity induced by D-Asp
and the antagonist of adenosine A 1 receptors (CPT) had no effect. The results indicated a different involvement of NMDA receptors on the L- or D-Asp-evoked
activation of ecto-5′-nucleotidase and on cellular damage. The adenosine formed from ecto-5′-nucleotidase stimulation preferentially
acted on adenosine A 2A receptor which is probably co-operating with the neurotoxicity induced by amino acids. 相似文献
8.
Docosahexaenoic acid (DHA) is important for central nervous system function during pathological states such as ischemia. DHA reduces neuronal injury in experimental brain ischemia; however, the underlying mechanisms are not well understood. In the present study, we investigated the effects of DHA on acute hippocampal slices subjected to experimental ischemia by transient oxygen and glucose deprivation (OGD) and re-oxygenation and the possible involvement of purinergic receptors as the mechanism underlying DHA-mediated neuroprotection. We observed that cellular viability reduction induced by experimental ischemia as well as cell damage and thiobarbituric acid reactive substances (TBARS) production induced by glutamate (10 mM) were prevented by hippocampal slices pretreated with DHA (5 μM). However, glutamate uptake reduction induced by OGD and re-oxygenation was not prevented by DHA. The beneficial effect of DHA against cellular viability reduction induced by OGD and re-oxygenation was blocked with PPADS (3 μM), a nonselective P2X 1–5 receptor antagonist as well as with a combination of TNP-APT (100 nM) plus brilliant blue (100 nM), which blocked P2X 1, P2X 3, P2X 2/3, and P2X 7 receptors, respectively. Moreover, adenosine receptors blockade with A 1 receptor antagonist DPCPX (100 nM) or with A 2B receptor antagonist alloxazine (100 nM) inhibited DHA-mediated neuroprotection. The addition of an A 2A receptor antagonist ZM241385 (50 nM), or A 3 receptor antagonist VUF5574 (1 μM) was ineffective. Taken together, our results indicated that neuroprotective actions of DHA may depend on P2X, A 1, and A 2B purinergic receptors activation. Our results reinforce the notion that dietary DHA may act as a local purinergic modulator in order to prevent neurodegenerative diseases. 相似文献
9.
Growing evidence has suggested a role in targeting the adenosine A 2A receptor for the treatment of Parkinson’s disease. The literature compounds KW 6002 ( 2) and ZM 241385 ( 5) were used as a starting point from which a series of novel ligands targeting the adenosine A 2A receptor were synthesized and tested in a recombinant human adenosine A 2A receptor functional assay. In order to further explore these molecules, we investigated the biological effects of assorted linkers attached to different positions on selected adenosine A 2A receptor antagonists, and assessed their potential binding modes using molecular docking studies. The results suggest that linking from the phenolic oxygen of selected adenosine A 2A receptor antagonists is relatively well tolerated due to the extension towards extracellular space, and leads to the potential of attaching further functionality from this position. 相似文献
10.
A 2A adenosine receptor (A 2AR), P2Y 1 receptor (P2Y 1R) and P2Y 12 receptor (P2Y 12R) are predominantly expressed on human platelets. The individual role of each of these receptors in platelet aggregation has been actively reported. Previously, hetero-oligomerization between these three receptors has been shown to occur. Here, we show that Ca 2+ signaling evoked by the P2Y 1R agonist, 2-methylthioladenosine 5’ diphosphate (2MeSADP) was significantly inhibited by the A 2AR antagonist (ZM241385 and SCH442416) and the P2Y 12R antagonist (ARC69931MX) using HEK293T cells expressing the three receptors. It was confirmed that inhibition of P2Y 1R signaling by A 2AR and P2Y 12R antagonists was indeed mediated through A 2AR and P2Y 12R using 1321N1 human astrocytoma cells which do not express P2Y receptors. We expect that intermolecular signal transduction and specific conformational changes occur among components of hetero-oligomers formed by these three receptors. 相似文献
11.
A new series of 1 H‐imidazol‐1‐yl substituted 8‐phenylxanthine analogs has been synthesized to study the effects of the imidazole group on the binding affinity of compounds for adenosine receptors. Competition binding studies of these compounds were carried out in vitro with human cloned receptors using [ 3H]DPCPX and [ 3H]ZM 241385 as radioligands at A 1 and A 2A adenosine receptors, respectively. The effect of the substitution pattern of the (imidazolyl)alkoxy group on various positions of the phenyl ring at C(8) was also studied. The xanthine derivatives displayed varying degrees of affinity and selectivity towards A 1 and A 2A receptor subtypes despite a common but variedly substituted Ar C(8). 相似文献
12.
The metabotropic glutamate receptors 5 (mGlu5Rs) and the adenosine A2A receptors (A2ARs) have been reported to functionally interact in the striatum. The aim of the present work was to verify the hypothesis that the state of activation of A2A Rs could influence mGlu5R-mediated effects in the striatum. In electrophysiological experiments (extracellular recording in rat corticostriatal slices), the ability of the selective mGlu5R agonist CHPG to potentiate the reduction of the field potential amplitude induced by NMDA was prevented not only by the selective mGlu5R antagonist MPEP, but also by the selective A2AR antagonist ZM 241385. Analogously, the application of CHPG potentiated NMDA-induced toxicity (measured by LDH release) in cultured striatal neurons, an effect that was abolished by both MPEP and ZM 241385. Finally, the A2AR agonist CGS 21680 potentiated CHGP effects, an action that was reproduced and abolished, respectively, by forskolin (an activator of the cAMP/protein kinase A, PKA, pathway) and KT 5720 (a PKA inhibitor). The results indicate that A2ARs exert a permissive role on mGlu5R-induced effects in the striatum. Such an interaction may represent an additional target for the development of therapeutic strategies towards striatal disorders. 相似文献
13.
BackgroundThis study was inspired by coalescing evidence that magnetic therapy may be a viable treatment option for certain diseases. This premise is based on the ability of moderate strength fields (i.e., 0.1 to 1 Tesla) to alter the biophysical properties of lipid bilayers and in turn modulate cellular signaling pathways. In particular, previous results from our laboratory (Wang et al., BMC Genomics, 10, 356 (2009)) established that moderate strength static magnetic field (SMF) exposure altered cellular endpoints associated with neuronal function and differentiation. Building on this background, the current paper investigated SMF by focusing on the adenosine A 2A receptor (A 2AR) in the PC12 rat adrenal pheochromocytoma cell line that displays metabolic features of Parkinson''s disease (PD). Methodology and Principal FindingsSMF reproduced several responses elicited by ZM241385, a selective A 2AR antagonist, in PC12 cells including altered calcium flux, increased ATP levels, reduced cAMP levels, reduced nitric oxide production, reduced p44/42 MAPK phosphorylation, inhibited proliferation, and reduced iron uptake. SMF also counteracted several PD-relevant endpoints exacerbated by A 2AR agonist {"type":"entrez-protein","attrs":{"text":"CGS21680","term_id":"878113053","term_text":"CGS21680"}}CGS21680 in a manner similar to ZM241385; these include reduction of increased expression of A 2AR, reversal of altered calcium efflux, dampening of increased adenosine production, reduction of enhanced proliferation and associated p44/42 MAPK phosphorylation, and inhibition of neurite outgrowth. Conclusions and SignificanceWhen measured against multiple endpoints, SMF elicited qualitatively similar responses as ZM241385, a PD drug candidate. Provided that the in vitro results presented in this paper apply in vivo, SMF holds promise as an intriguing non-invasive approach to treat PD and potentially other neurological disorders. 相似文献
14.
The adenosine A 2A receptor (A 2AR) is a G-protein-coupled receptor that plays a key role in transmembrane signalling mediated by the agonist adenosine. The structure of A 2AR was determined recently in an antagonist-bound conformation, which was facilitated by the T4 lysozyme fusion in cytoplasmic loop 3 and the considerable stabilisation conferred on the receptor by the bound inverse agonist ZM241385. Unfortunately, the natural agonist adenosine does not sufficiently stabilise the receptor for the formation of diffraction-quality crystals. As a first step towards determining the structure of A 2AR bound to an agonist, the receptor was thermostabilised by systematic mutagenesis in the presence of the bound agonist [ 3H]5'-N-ethylcarboxamidoadenosine (NECA). Four thermostabilising mutations were identified that when combined to give mutant A 2AR-GL26, conferred a greater than 200-fold decrease in its rate of unfolding compared to the wild-type receptor. Pharmacological analysis suggested that A 2AR-GL26 is stabilised in an agonist-bound conformation because antagonists bind with up to 320-fold decreased affinity. None of the thermostabilising mutations are in the ZM241385 binding pocket, suggesting that the mutations affect ligand binding by altering the conformation of the receptor rather than through direct interactions with ligands. A 2AR-GL26 shows considerable stability in short-chain detergents, which has allowed its purification and crystallisation. 相似文献
15.
The A 2A adenosine receptor (A 2AAR) is a unique G‐protein coupled receptor (GPCR), because besides agonist, its antagonist could also lead to therapeutic relevance. Based on A 2AAR‐antagonist crystal structure, we have studied the binding mechanism of two distinct antagonists, ZM241385 and KW6002, and dynamic behaviors of A 2AAR induced by antagonist binding. Key residues interacting with both antagonists and residues specifically binding to one of them are identified. ZM241385 specifically bound to S67 2.65, M177 5.38, and N253 6.55, while KW6002 binds to F62 2.60, A81 3.29, and H264 7.29. Moreover, interactions with L167 5.28 are found for both antagonists, which were not reported in agonist binding. The dynamic behaviors of antagonist bound holo‐A 2AARs were found to be different from the apo‐A 2AAR in three typical functional switches, (i) the “ionic lock” was in equilibrium between formation and breakage in apo‐A 2AAR, but stayed broken in holo‐A 2AARs; (ii) the “rotamer toggle switch,” T88 3.36/F242 6.44/W246 6.48, adopted different rotameric conformations in apo‐A 2AAR and holo‐A 2AARs; (iii) apo‐A 2AAR preferred α‐helical intracellular loop (IC)2 and flexible IC3, while holo‐A 2AARs had a flexible IC2 and α‐helical IC3. Our results indicated that antagonist binding induced different conformational rearrangements of these characteristic functional switches in apo‐A 2AAR and holo‐A 2AARs. Proteins 2013; 81:1399–1410. © 2013 Wiley Periodicals, Inc. 相似文献
16.
BackgroundThe inhibitory effect of adenosine on platelet aggregation is abrogated after the addition of adenosine-deaminase. Inosine is a naturally occurring nucleoside degraded from adenosine. ObjectivesThe mechanisms of antiplatelet action of adenosine and inosine in vitro and in vivo, and their differential biological effects by molecular modeling were investigated. ResultsAdenosine (0.5, 1 and 2 mmol/L) inhibited phosphatidylserine exposure from 52±4% in the control group to 44±4 (p<0.05), 29±2 (p<0.01) and 20±3% (p<0.001). P-selectin expression in the presence of adenosine 0.5, 1 and 2 mmol/L was inhibited from 32±4 to 27±2 (p<0.05), 14±3 (p<0.01) and 9±3% (p<0.001), respectively. At the concentrations tested, only inosine to 4 mmol/L had effect on platelet P-selectin expression (p<0.05). Adenosine and inosine inhibited platelet aggregation and ATP release stimulated by ADP and collagen. Adenosine and inosine reduced collagen-induced platelet adhesion and aggregate formation under flow. At the same concentrations adenosine inhibited platelet aggregation, decreased the levels of sCD40L and increased intraplatelet cAMP. In addition, SQ22536 (an adenylate cyclase inhibitor) and ZM241385 (a potent adenosine receptor A 2A antagonist) attenuated the effect of adenosine on platelet aggregation induced by ADP and intraplatelet level of cAMP. Adenosine and inosine significantly inhibited thrombosis formation in vivo (62±2% occlusion at 60 min [n = 6, p<0.01] and 72±1.9% occlusion at 60 min, [n = 6, p<0.05], respectively) compared with the control (98±2% occlusion at 60 min, n = 6). A 2A is the adenosine receptor present in platelets; it is known that inosine is not an A 2A ligand. Docking of adenosine and inosine inside A 2A showed that the main difference is the formation by adenosine of an additional hydrogen bond between the NH 2 of the adenine group and the residues Asn253 in H6 and Glu169 in EL2 of the A 2A receptor. ConclusionTherefore, adenosine and inosine may represent novel agents lowering the risk of arterial thrombosis. 相似文献
17.
Prior studies demonstrate that adenosine, acting at one or more of its receptors, mediates the anti-inflammatory effects of
methotrexate in animal models of both acute and chronic inflammation. Both adenosine A 2A and A 3 receptors contribute to the anti-inflammatory effects of methotrexate treatment in the air pouch model of inflammation, and
the regulation of inflammation by these two receptors differs at the cellular level. Because different factors may regulate
inflammation at different sites we examined the effect of low-dose weekly methotrexate treatment (0.75 mg/kg/week) in a model
of acute peritoneal inflammation in adenosine A 2A receptor knockout mice and A 3 receptor knockout mice and their wild-type littermates. Following intraperitoneal injection of thioglycollate there was no
significant difference in the number or type of leukocytes, tumor necrosis factor alpha (TNF-α) and IL-10 levels that accumulated
in the thioglycollate-induced peritoneal exudates in adenosine A 2A knockout mice or wild-type control mice. In contrast, there were more leukocytes, TNF-α and IL-10 in the exudates of the
adenosine A 3 receptor-deficient mice. Low-dose, weekly methotrexate treatment increased the adenosine concentration in the peritoneal
exudates of all mice studied, and reduced the leukocyte accumulation in the wild-type mice and A 3 receptor knockout mice but not in the A 2A receptor knockout mice. Methotrexate reduced exudate levels of TNF-α in the wild-type mice and A 3 receptor knockout mice but not the A 2A receptor knockout mice. More strikingly, IL-10, a critical regulator of peritoneal inflammation, was increased in the methotrexate-treated
wild-type mice and A 3 knockout mice but decreased in the A 2A knockout mice. Dexamethasone, an agent that suppresses inflammation by a different mechanism, was similarly effective in
wild-type mice, A 2A mice and A 3 knockout mice. These findings provide further evidence that adenosine is a potent regulator of inflammation that mediates
the anti-inflammatory effects of methotrexate. Moreover, these data provide strong evidence that the anti-inflammatory effects
of methotrexate and adenosine are mediated by different receptors in different inflammatory loci, an observation that may
explain why inflammatory diseases of some organs but not of other organs respond to methotrexate therapy. 相似文献
18.
This study was aimed to investigate the underlying mechanism of vasodilation induced by the activation of A(2B) adenosine receptors in relation to cerebral blood flow (CBF) autoregulation. Changes in pial arterial diameters were observed directly through a closed cranial window. N(omega)-nitro-L-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor) significantly suppressed the concentration-dependent vasodilations induced by adenosine and 5'-N-ethylcarboxamido-adenosine (NECA) but not the vasodilation by CGS-21680 (A(2A)-receptor agonist). Moreover, NECA-induced vasodilation was suppressed by alloxazine (1 micromol/l) but not by ZM-241385 (1 micromol/l, A(2A) antagonist), which suggests mediation by A(2B)- receptor activation. Otherwise, the level of nitrite/nitrate was concentration dependently increased in the artificial cerebrospinal fluid (CSF) when adenosine and NECA were suffused over the cortical surface. L-NAME and alloxazine, but not ZM-241385, largely inhibited their releases. The lower limit of CBF autoregulation was little affected following pretreatment with L-NAME or alloxazine. Thus it is suggested that adenosine-induced vasodilation via activation of A(2B)-adenosine receptors of the rat pial artery is coupled to the production of nitric oxide, which contributes little to CBF autoregulation. 相似文献
19.
We have characterized the binding of [2-(3)H]-4-(2-[7-Amino-2-(2-furyl)-[1,2,4]-triazolo-[2,3-a]-[1,3,5]-triazin-5-ylamino]ethyl)phenol ([(3)H]ZM241385) to adenosine A(2A) receptors in membranes of rat striatum and transfected CHO cells. Saturation experiments showed that [(3)H]ZM241385 binds to a single class of binding sites with high affinity (K(d) = 0.23 nM and 0.14 nM in CHO cell and striatal membranes, respectively). The membranes of CHO cells required pretreatment with adenosine deaminase (ADA) to achieve high-affinity binding, while ADA had no influence on the ligand binding properties in striatal membranes. The binding of [(3)H]ZM241385 was fast and reversible, achieving equilibrium within 20 minutes at all radioligand concentrations. The kinetic analysis of the [(3)H]ZM241385 interaction with A(2A) receptors indicated that the reaction had at least two subsequent steps. The first step corresponds to a fast equilibrium, which also determines the antagonist potency to competitively inhibit CGS21680-induced accumulation of cAMP (first equilibrium constant K(A) = 6.6 nM). The second step corresponds to a slow process of conformational isomerization (equilibrium constant K(i) = 0.03). The combination of the two steps gives the dissociation constant K(d) = 0.20 nM based on the kinetic data, which is in good agreement with the directly measured value. The data obtained shed light on the mechanism of the [(3)H]ZM241385 interaction with adenosine A(2A) receptors from different sources in vitro. The isomerization step of the A(2A) antagonist radioligand binding has to be taken into account for the interpretation of the binding parameters obtained from the various competition assays and explain the discrepancy between antagonist affinity in saturation experiments versus its potency in functional assays. 相似文献
20.
ATP is thought to be released to the extracellular compartment by neurons and astrocytes during neural activation. We examined whether ATP exerts its effect of promoting pial arteriolar dilation (PAD) directly or upon conversion (via ecto-nucleotidase action) to AMP and adenosine. Blockade of extracellular direct ATP to AMP conversion, with ARL-67156, significantly reduced sciatic nerve stimulation-evoked PADs by 68%. We then monitored PADs during suffusions of ATP, ADP, AMP, and adenosine in the presence and absence of the following: 1) the ecto-5'-nucleotidase inhibitor α,β-methylene adenosine 5'-diphosphate (AOPCP), 2) the A(2) receptor blocker ZM 241385, 3) the ADP P2Y(1) receptor antagonist MRS 2179, and 4) ARL-67156. Vasodilations induced by 1 and 10 μM, but not 100 μM, ATP were markedly attenuated by ZM 241385, AOPCP, and ARL-67156. Substantial loss of reactivity to 100 μM ATP required coapplications of ZM 241385 and MRS 2179. Dilations induced by ADP were blocked by MRS 2179 but were not affected by either ZM 241385 or AOPCP. AMP-elicited dilation was partially inhibited by AOPCP and completely abolished by ZM 241385. Collectively, these and previous results indicate that extracellular ATP-derived adenosine and AMP, via A(2) receptors, play key roles in neural activation-evoked PAD. However, at high extracellular ATP levels, some conversion to ADP may occur and contribute to PAD through P2Y(1) activation. 相似文献
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