Selective Adenosine A1 Receptor Antagonist Research Articles

Combined antagonism of glutamate mGlu5 and adenosine A2A receptors interact to regulate alcohol-seeking in rats

Adenosine and glutamate have been implicated as mediators involved in the self-administration of alcohol. In the present study we sought to determine whether adenosine receptors could interact with metabotropic glutamate receptors to regulate operant responding for alcohol and also the integration of the salience of alcohol-paired cues. Alcohol-preferring (iP) rats were trained to self-administer alcohol under operant conditions. The availability of alcohol was paired with an olfactory cue plus a stimulus light. Rats were examined under fixed ratio responding and also following extinction under a cue-induced reinstatement paradigm. Administration of the selective adenosine A2A receptor antagonist, SCH 58261, reduced fixed ratio responding for alcohol in iP rats in a dose-related manner. Furthermore, the combination of a subthreshold dose of SCH 58261 with a subthreshold dose of the mGlu5 receptor antagonist MTEP also reduced alcohol self-administration and increased the latency to the first reinforced response, suggesting a pre-ingestive effect. Moreover, this combination of SCH 58261 and MTEP also prevented the conditioned reinstatement of alcohol-seeking elicited by the re-presentation of cues previously paired with alcohol availability. In contrast, combinations of the selective adenosine A1 receptor antagonist, DPCPX, with either SCH 58261 or MTEP had no effect on alcohol responding. Collectively, these data suggest a functional interaction between adenosine A2A and mGlu5 receptors in relation to alcohol-seeking and the integration of the drug-related cues.

Role of Adenosine Receptor Subtypes in Rat Jejunum in Unfed State Versus Glucose-Induced Hyperemia

Adenosine is a key mediator in intestinal absorptive hyperemia. This study examines the role of adenosine receptor subtypes in the intestinal microvasculature at rest (unfed) and during glucose exposure. Intravital video microscopy was used to record vascular responses in the rat jejunum in unfed resting states versus active glucose absorption. Two series of experiments were performed: topical adenosine alone and with adenosine receptor antagonists, and topical glucose alone and with adenosine receptor antagonists. We found that distal premucosal arterioles were more reactive to adenosine than were larger inflow arterioles. The selective A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (200 nm), and the A2b receptor antagonist, alloxazine (60 microm), decreased the sensitivity and reactivity of the inflow and premucosal arterioles to adenosine, whereas the selective A2a receptor antagonist 8-(3-chlorostyryl)caffeine (CSC) (200 nm) had no effect on inflow arteriole diameter and only slightly reduced the premucosal arteriolar sensitivity to adenosine. As previously observed, isotonic glucose caused vasodilation (24 +/- 3.4% of the control) in the distal premucosal arterioles. Conversely, premucosal arterioles did not dilate during exposure of the intestine to isotonic mannitol solution that is not actively absorbed. Adenosine A2a RA CSC and A2b RA alloxazine attenuated glucose-induced vasodilation, whereas adenosine A1 RA DPCPX completely abolished glucose-induced dilation. These findings suggest that resting tone in premucosal vessels appears to be responsive to adenosine mediation rather than inflow arteriolar tone; the adenosine A1, A2a, and A2b receptors all contribute to adenosine-mediated vasodilation in the intestine, with the greatest attenuation seen with A1 receptor antagonism; and other vasoactive mediators might also contribute to glucose-induced jejunal vasodilation, and interaction might exist between adenosine receptors and other mediators.

Role of P2 purinergic receptors in synaptic transmission under normoxic and ischaemic conditions in the CA1 region of rat hippocampal slices

The role of ATP and its stable analogue ATPγS [adenosine-5′-o-(3-thio)triphosphate] was studied in rat hippocampal neurotransmission under normoxic conditions and during oxygen and glucose deprivation (OGD). Field excitatory postsynaptic potentials (fEPSPs) from the dendritic layer or population spikes (PSs) from the soma were extracellularly recorded in the CA1 area of the rat hippocampus. Exogenous application of ATP or ATPγS reduced fEPSP and PS amplitudes. In both cases the inhibitory effect was blocked by the selective A1 adenosine receptor antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine) and was potentiated by different ecto-ATPase inhibitors: ARL 67156 (6-N,N-diethyl-D-β,γ-dibromomethylene), BGO 136 (1-hydroxynaphthalene-3,6-disulfonate) and PV4 [hexapotassium dihydrogen monotitanoundecatungstocobaltate(II) tridecahydrate, K6H2[TiW11CoO40]·13H2O]. ATPγS-mediated inhibition was reduced by the P2 antagonist suramin [8-(3-benzamido-4-methylbenzamido)naphthalene-1,3,5-trisulfonate] at the somatic level and by other P2 blockers, PPADS (pyridoxalphosphate-6-azophenyl-2′,4′-disulfonate) and MRS 2179 (2′-deoxy-N6-methyladenosine 3′,5′-bisphosphate), at the dendritic level. After removal of both P2 agonists, a persistent increase in evoked synaptic responses was recorded both at the dendritic and somatic levels. This effect was prevented in the presence of different P2 antagonists. A 7-min OGD induced tissue anoxic depolarization and was invariably followed by irreversible loss of fEPSP. PPADS, suramin, MRS2179 or BBG (brilliant blue G) significantly prevented the irreversible failure of neurotransmission induced by 7-min OGD. Furthermore, in the presence of these P2 antagonists, the development of anoxic depolarization was blocked or significantly delayed. Our results indicate that P2 receptors modulate CA1 synaptic transmission under normoxic conditions by eliciting both inhibitory and excitatory effects. In the same brain region, P2 receptor stimulation plays a deleterious role during a severe OGD insult.

2-triazole-substituted adenosines: a new class of selective A3 adenosine receptor agonists, partial agonists, and antagonists.

"Click chemistry" was explored to synthesize two series of 2-(1,2,3-triazolyl)adenosine derivatives (1-14). Binding affinity at the human A(1), A(2A), and A(3)ARs (adenosine receptors) and relative efficacy at the A(3)AR were determined. Some triazol-1-yl analogues showed A(3)AR affinity in the low nanomolar range, a high ratio of A(3)/A(2A) selectivity, and a moderate-to-high A(3)/A(1) ratio. The 1,2,3-triazol-4-yl regiomers typically showed decreased A(3)AR affinity. Sterically demanding groups at the adenine C2 position tended to reduce relative A(3)AR efficacy. Thus, several 5'-OH derivatives appeared to be selective A(3)AR antagonists, i.e., 10, with 260-fold binding selectivity in comparison to the A(1)AR and displaying a characteristic docking mode in an A(3)AR model. The corresponding 5'-ethyluronamide analogues generally showed increased A(3)AR affinity and behaved as full agonists, i.e., 17, with 910-fold A(3)/A(1) selectivity. Thus, N(6)-substituted 2-(1,2,3-triazolyl)adenosine analogues constitute a novel class of highly potent and selective nucleoside-based A(3)AR antagonists, partial agonists, and agonists.

Pyrazolo-triazolo-pyrimidines as adenosine receptor antagonists: A complete structure-activity profile.

In the last 5 years, many efforts have been conducted searching potent and selective human A3 adenosine antagonists. In this field several different classes of compounds, possessing very good affinity (nM range) and with a broad range of selectivity, have been proposed. Recently, our group synthesized a new series of pyrazolo-triazolo-pyrimidines bearing different substitutions at the N5 and N8 positions, which have been described as highly potent and selective human A3 adenosine receptor antagonists. The present review summarizes available data and provides an overview of the structure–activity relationships found for this class of human A3 adenosine receptor antagonists.

Potent and Orally Bioavailable 8-Bicyclo[2.2.2]octylxanthines as Adenosine A1 Receptor Antagonists

In the search for a selective adenosine A1 receptor antagonist with greater aqueous solubility than the compounds currently in clinical trials as diuretics, a series of 1,4-substituted 8-cyclohexyl and 8-bicyclo[2.2.2]octylxanthines were investigated. The binding affinities of a variety of cyclohexyl and bicyclo[2.2.2]octylxanthines for the rat and human adenosine A1, A2A, A2B, and A3 receptors are presented. Bicyclo[2.2.2]octylxanthine 16 exhibited good pharmaceutical properties and in vivo activity in a rat diuresis model (ED50=0.3 mg/kg po). Optimization of the bridgehead substituent led to propionic acid 29 (BG9928), which retained high potency (hA1, Ki=7 nM) and selectivity for the adenosine A1 receptor (915-fold versus adenosine A2A receptor; 12-fold versus adenosine A2B receptor) with improved oral efficacy in the rat diuresis model (ED50=0.01 mg/kg) as well as high oral bioavailability in rat, dog, and cynomolgus monkey.

Tricyclic Imidazoline Derivatives as Potent and Selective Adenosine A1 Receptor Antagonists

Novel tricyclic imidazoline antagonists of the adenosine A1 receptor are described. For key compounds, the selectivity level over other adenosine receptor subtypes is examined along with their in vivo effects in a rat diuresis model. Compound 14, the (R)-isomer of 7,8-dihydro-8-ethyl-2-(4-bicyclo[2.2.2]octan-1-ol)-4-propyl-1H-imidazo[2,1-i]purin-5(4H)-one, is a particularly potent adenosine A1 receptor antagonist with good selectivity over the other three adenosine receptor subtypes: A1 (human) Ki=22 nM; A2A (human) Ki=4400 nM; A2B (human) Ki=580 nM; A3 (human) Ki>or=10,000 nM. Imidazoline 14 is a competitive adenosine A1 receptor antagonist with a pA2 value of 8.88 and is highly soluble in water (>100 mg/mL). In addition, it has an oral bioavailability of 84% and an oral half-life of 3.8 h in rats. When orally administered in a rat diuresis model, compound 14 promoted sodium excretion (ED50=0.01 mg/kg). This level of efficacy is comparable to that of BG9928, a selective adenosine A1 receptor antagonist that is currently in clinical trials as a treatment for congestive heart failure. Additional modifications to 14 also showed that the bridgehead hydroxyl group could be replaced with a propionic acid (compound 36) without a significant loss in binding affinity or in vivo activity.

Intrahepatic adenosine-mediated activation of hepatorenal reflex is via A1 receptors in rats

Previous studies have shown that intrahepatic adenosine is involved in activation of the hepatorenal reflex that regulates renal sodium and water excretion. The present study aims to determine which subtype of adenosine receptors is implicated in the process. Mean arterial pressure, portal venous pressure and flow, and renal arterial flow were monitored in pentobarbital anesthetized rats. Urine was collected from the bladder. Intraportal administration of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective adenosine A1 receptor antagonist, increased urine flow by 24%, 89%, and 143% at the dose of 0.01, 0.03, and 0.1 mg x kg(-1), respectively; in contrast, DPCPX, when administered intravenously at the same doses, only increased urine flow by 0%, 18%, and 36%. The increases in urine flow induced by intraportal administration of DPCPX were abolished in rats with liver denervation. Intrahepatic infusion of adenosine significantly decreased urine flow and this response was abolished by intraportal administration of DPCPX. Neither intraportal nor intravenous administration of 3,7-dimethyl-1-propargylxanthine, a selective adenosine A2 receptor antagonist, showed significant influence on urine flow. Systemic arterial pressure, renal blood flow and glomerular filtration rate were unaltered by the administration of any of the drugs. In conclusion, intrahepatic adenosine A1 receptors are responsible for the adenosine-mediated hepatorenal reflex that regulates renal water and sodium excretion.

Involvement of adenosine in depression of synaptic transmission during hypercapnia in isolated spinal cord of neonatal rats

Adenosine is one of the most important neuromodulators in the CNS, both under physiological and pathological conditions. In the isolated spinal cord of the neonatal rat in vitro, acute hypercapnic acidosis (20% CO2, pH 6.7) reversibly depressed electrically evoked spinal reflex potentials. This depression was partially reversed by 8-cyclopentlyl-1,3-dimethylxanthine (CPT), a selective A1 adenosine receptor antagonist. Isohydric hypercapnia (20% CO2, pH 7.3), but not isocapnic acidosis (5% CO2, pH 6.7), depressed the reflex potentials, which were also reversed by CPT. An ecto-5'-nucleotidase inhibitor did not affect the hypercapnic acidosis-evoked depression. An inhibitor of adenosine kinase, but not deaminase, mimicked the inhibitory effect of hypercapnic acidosis on the spinal reflex potentials. Accumulation of extracellular adenosine and inhibition of adenosine kinase activity were caused by hypercapnic acidosis and isohydric hypercapnia, but not isohydric acidosis. These results indicate that the activation of adenosine A1 receptors is involved in the hypercapnia-evoked depression of reflex potentials in the isolated spinal cord of the neonatal rat. The inhibition of adenosine kinase activity is suggested to cause the accumulation of extracellular adenosine during hypercapnia.

Adenosine and dialysis hypotension

In this issue, Imai et al. report the results of a double-blind placebo-controlled study on the effect of an adenosine A1 receptor antagonist, FK352, on the incidence of dialysis hypotension in hypotension-prone patients. This Commentary discusses the use of selective adenosine A1 receptor antagonists for the prevention of dialysis hypotension from the perspective of the potential role of adenosine in its pathogenesis.

IB‐MECA and MRS1191 do not Act on Rat Microvascular Adenosine A 3 Receptors Exclusively

The adenosine (ADO) A3 receptors on mast cells have been shown to mediate ADO-induced arteriolar vasoconstriction and increase in cutaneous vascular permeability. To determine whether a similar role exists for ADO A3 receptors in the regulation of permeability responses to ADO of arterioles and venules isolated from juvenile female rat skeletal muscle, permeability to albumin (Ps) was determined duringADO (10−5 M) suffusion without and with a selective ADO A3 receptor antagonist, MRS1191 (10−7 M). Consistent with ADO A3 receptor mediation of Ps response to ADO, MRS1191 abolished the ADO-induced decrease in arteriolar (n=5) and venular (n=4) Ps. However, IB-MECA (10−7 M), a selective ADO A3 receptor agonist, alone, increased arteriolar Ps (n=7) and decreased venular Ps (n=7), a result inconsistent with the MRS1191 data. In addition, we demonstrated previously that microvessel Ps responses to ADO are blocked by 8-SPT (nonselective ADO A1 and A2 receptor antagonist) or ZM241385 (a selective ADO A2A receptor antagonist) (FASEB, Abstract 127.8, 2005). CGS21680, a selective ADO A2A receptor agonist, also decreased Ps of both microvessel subtypes. In aggregate, these data demonstrate that the putative ADO A3 receptor agonist and antagonist, respectively, are inducing mixed responses resulting from involvement of A2A receptors on abdominal skeletal muscle arterioles and venules from juvenile female rats (Supported by NIH RO1HL078816, HL075186, 1CO6RR017353 and NASA NNJ05HF37G)

Neuroanesthesia and Intensive Care Isoflurane tolerance against focal cerebral ischemia is attenuated by adenosine A1 receptor antagonists

PurposeTo investigate the role of the adenosine A1 receptor in the rapid tolerance to cerebral ischemia induced by isoflurane preconditioning.MethodsSeventy-five rats were randomly assigned into five groups (n = 15 each): Control, 8-cyclopentyl-1,3-dipropulxanthine (DPCPX), Isoflurane, DPCPX+Isoflurane and Vehicle+Isoflurane groups. All animals underwent right middle cerebral artery occlusion (MCAO) for two hours. Isoflurane preconditioning was conducted one hour before MCAO in Isoflurane, DPCPX+Isoflurane and Vehicle+Isoflurane groups by exposing the animals to 1.5% isoflurane in 98% oxygen for one hour. In the Control and DPCPX groups, animals were exposed to 98% oxygen one hour before MCAO for one hour. A selective adenosine A1 receptor antagonist, DPCPX, was administered (0.1 mg·kg-1) 15 min before isoflurane/oxygen exposure in the DPCPX and DPCPX+Isofluranegroups to evaluate the effect of adenosine A1 receptor antagonist on isoflurane preconditioning. Dimethyl sulfoxide, the solvent of DPCPX, was administered (1 mL·kg-1) 15 min before isoflurane exposure in the Vehicle+Isoflurane group. Neurological deficit scores and brain infarct volumes were evaluated 24 hr after reperfusion.ResultsAnimals in the Isoflurane and Vehicle+Isoflurane groups developed lower neurological deficit scores and smaller brain infarct volumes than the Control group (P < 0.01). Animals in the DPCPX+Isoflurane group developed higher neurological deficit scores and larger brain infarct volumes than the Isoflurane and Vehicle+Isoflurane groups (P < 0.01).ConclusionThe present study demonstrates that preconditioning with isoflurane reduces focal cerebral ischemic injury in rats, and the adenosine A1 receptor antagonist (DPCPX) attenuates the neuroprotection induced by isoflurane preconditioning.

Activation of Adenosine A1 Receptors Reduces Anxiety-Like Behavior During Acute Ethanol Withdrawal (Hangover) in Mice

Elevated signs of anxiety are observed in both humans and rodents during withdrawal from chronic as well as acute ethanol exposure, and it represents an important motivational factor for ethanol relapse. Several reports have suggested the involvement of brain adenosine receptors in different actions produced by ethanol such as motor incoordination and hypnotic effects. In addition, we have recently demonstrated that adenosine A1 receptors modulate the anxiolytic-like effect induced by ethanol in mice. In the present study, we evaluated the potential of adenosine A1 and A2A receptor agonists in reducing the anxiety-like behavior during acute ethanol withdrawal (hangover) in mice. Animals received a single intraperitoneal administration of saline or ethanol (4 g/kg) and were tested in the elevated plus maze after an interval of 0.5-24 h. The results indicated that hangover-induced anxiety was most pronounced between 12 and 18 h after ethanol administration, as indicated by a significant reduction in the exploration of the open arms of the maze. At this time interval, ethanol was completely cleared. The acute administration of 'nonanxiolytic' doses of adenosine and the selective adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA), but not the adenosine A2A receptor agonist N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl]adenosine (DPMA), at the onset of peak withdrawal (18 h), reduced this anxiogenic-like response. In addition, the effect of CCPA on the anxiety-like behavior of ethanol hangover was reversed by pretreatment with the selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). These results reinforce the notion of the involvement of adenosine receptors in the anxiety-like responses and indicate the potential of adenosine A1 receptor agonists to reduce the anxiogenic effects during ethanol withdrawal.

Altered intravenous pharmacokinetics of topotecan in rats with acute renal failure (ARF) induced by uranyl nitrate: Do adenosine A1 antagonists (selective/non-selective) normalize the altered topotecan kinetics in ARF?

A series of exploratory investigations with multiple agents was carried out in normal rats and in rats with uranyl nitrate-induced acute renal failure to understand the disposition characteristics of intravenous topotecan (TPT) used as a model substrate. The disposition of TPT was unaltered in normal rats when treated with methotrexate, whereas treatment with probenecid increased the systemic exposure of TPT. In case of uranyl nitrate-induced acute renal failure (UN-ARF) rats, the systemic exposure of TPT was increased when compared with normal rats, whereas in UN-ARF rats treated with probenecid a further reduction in renal clearance of TPT was noted as compared with that of UN-ARF induced rats. Thus, TPT may be involved in the tubular secretory pathway when a passive glomerular filtration pathway for elimination was not possible. The disposition of TPT did not normalize in UN-ARF rats when treated with caffeine, a non-selective adenosine A1 receptor antagonist, whereas the selective adenosine A1 receptor antagonist (1,3-dipropyl-8-phenylxanthine, DPPX) normalized TPT pharmacokinetic disposition by improving renal function. Renal excretion studies demonstrated that CLR improved by almost fivefold following DPPX treatment in ARF rats. In addition, the qualitative stability/metabolism pattern of TPT in liver microsomes prepared from various groups of rats (normal rats, UN-ARF rats, rats treated with DPPX, and UN-ARF rats treated with DPPX) was found to be similar. In summary, using a pharmacokinetic tool as a surrogate, it has been shown that the pharmacokinetic disposition of TPT improved considerably upon treatment with DPPX, a selective adenosine A1 antagonist.

Activation of receptors negatively coupled to adenylate cyclase is required for induction of long-term synaptic depression at Schaffer collateral-CA1 synapses

Chemical LTD (CLTD) of synaptic transmission is triggered by simultaneously increasing presynaptic [cGMP] while inhibiting PKA. Here, we supply evidence that class II, but not III, metabotropic glutamate receptors (mGluRs), and A1 adenosine receptors, both negatively coupled to adenylate cyclase, play physiologic roles in providing PKA inhibition necessary to promote the induction of LTD at Schaffer collateral-CA1 synapses in hippocampal slices. Simultaneous activation of group II mGluRs with the selective agonist (2S,2'R,3'R)-2-(2',3'-dicarboxy-cyclopropyl) glycine (DCGIV; 5 microM), while raising [cGMP] with the type V phosphodiesterase inhibitor, zaprinast (20 microM), resulted in a long-lasting depression of synaptic strength. When zaprinast (20 microM) was combined with a cell-permeant PKA inhibitor H-89 (10 microM), the need for mGluR IIs was bypassed. DCGIV, when combined with a "submaximal" low frequency stimulation (1 Hz/400 s), produced a saturating LTD. The mGluR II selective antagonist, (2S)-alpha-ethylglutamic acid (EGLU; 5 microM), blocked induction of LTD by prolonged low frequency stimulation (1 Hz/900 s). In contrast, the mGluR III selective receptor blocker, (RS)-a-Cyclopropyl-[3- 3H]-4-phosphonophenylglycine (CPPG; 10 microM), did not impair LTD. The selective adenosine A1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 100 nM), also blocked induction of LTD, while the adenosine A1 receptor agonist N6-cyclohexyl adenosine (CHA; 50 nM) significantly enhanced the magnitude of LTD induced by submaximal LFS and, when paired with zaprinast (20 microM), was sufficient to elicit CLTD. Inhibition of PKA with H-89 rescued the expression of LTD in the presence of either EGLU or DPCPX, confirming the hypothesis that both group II mGluRs and A1 adenosine receptors enhance the induction of LTD by inhibiting adenylate cyclase and reducing PKA activity.

Neuroprotective effect of paeoniflorin on cerebral ischemic rat by activating adenosine A1 receptor in a manner different from its classical agonists

The effects of paeoniflorin (PF), a compound isolated from Paeony radix, on neurological impairment and histologically measured infarction volume following transient and permanent focal ischemia were examined in Sprague-Dawley rats. In transient ischemia model, rats were subjected to a 1.5-h occlusion of the middle cerebral artery (MCA). The administration of PF (2.5 and 5 mg kg(-1), s.c.) produced a dose-dependent decrease in both neurological impairment and the histologically measured infarction volume. Similar results were also obtained when PF (2.5, 5, and 10 mg kg(-1), s.c.) was given in permanent ischemia model. The neuroprotective effect of PF (10 mg kg(-1), s.c.) was abolished by pretreatment of DPCPX (0.25 mg kg(-1), s.c.), a selective adenosine A1 receptor (A1R) antagonist. PF (10, 40, and 160 mg kg(-1), i.v.) had no effect on mean arterial pressure (MAP) and heart rates (HR) in the conscious rat. Additionally, PF (10(-3) mol l(-1)) had no effect on noradrenaline- (NA-) or high K+ concentration-induced contractions of isolated rabbit primary artery. In competitive binding experiments, PF did not compete with the binding of [3H]DPCPX, but displaced the binding of [3H]NECA to the membrane preparation of rat cerebral cortex. This binding manner was distinguished from the classical A1R agonists. The results demonstrated that activation of A1R might be involved in PF-induced neuroprotection in cerebral ischemia in rat. However, PF had no 'well-known' cardiovascular side effects of classical A1R agonists. The results suggest that PF might have the potential therapeutic value as an anti-stroke drug.

Phase-specific central regulatory systems of hibernation in Syrian hamsters

The central body temperature ( T b) regulation system during hibernation was investigated in Syrian hamsters of either sex. Hibernation induced in Syrian hamsters by housing them in a cold room under short day-light/dark cycle was confirmed by marked reductions in the heart rate, T b and respiratory rate. The hibernation of hamsters was classified into (i) entrance, (ii) maintenance and (iii) arousal phases according to T b changes. In hibernating hamsters, T b elevations were phase-selectively elicited by intracerebroventricular (ICV) injection of 8-cyclopenthyltheophylline (CPT; a selective A1-adenosine receptor antagonist) and naloxone (a non-selective opioid receptor antagonist) during the entrance and maintenance phases, respectively. Moreover, a similar T b elevation tendency during the maintenance phase was also induced by ICV naloxonazine, (a selective μ1-opioid receptor antagonist), although such was not the case for naltrindole (a selective δ-opioid receptor antagonist) or nor-binaltorphimine (nor-BNI, a selective κ-opioid receptor antagonist). Furthermore, T b elevations in hibernating hamsters were similarly induced with ICV thyrotropin-releasing hormone (TRH) during the entrance and maintenance phases. Furthermore, ICV injection of the anti-TRH antibody ameliorated the T b elevations induced by tactile stimulation. These results suggest that activation of the A1-receptor by adenosine is important for the generation of hypothermia in the entrance phase, and that activation of the μ1-opioid receptor by opioid peptides is required for perpetuation of hypothermia in the maintenance phase. In addition, TRH is a key endogenous substance involved in T b elevations during the arousal phase of hibernating hamsters.

Distinct molecular phenotype of malignant CD34+ hematopoietic stem and progenitor cells in chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is a malignant disorder of the hematopoietic stem cell characterized by the BCR-ABL oncogene. We examined gene expression profiles of highly enriched CD34(+) hematopoietic stem and progenitor cells from patients with CML in chronic phase using cDNA arrays covering 1.185 genes. Comparing CML CD34(+) cells with normal CD34(+) cells, we found 158 genes which were significantly differentially expressed. Gene expression patterns reflected BCR-ABL-induced functional alterations such as increased cell-cycle and proteasome activity. Detoxification enzymes and DNA repair proteins were downregulated in CML CD34(+) cells, which might contribute to genetic instability. Decreased expression of junction plakoglobulin and CXC chemokine receptor 4 (CXCR-4) might facilitate the release of immature precursors from bone marrow in CML. GATA-2 was upregulated in CML CD34(+) cells, suggesting an increased self-renewal in comparison with normal CD34(+) cells. Moreover, we found upregulation of the proto-oncogene SKI and of receptors for neuromediators such as opioid mu1 receptor, GABA B receptor, adenosine A1 receptor, orexin 1 and 2 receptors and corticotropine-releasing hormone receptor. Treatment of CML progenitor cells with the selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) resulted in a dose-dependent significant inhibition of clonogenic growth by 40% at a concentration of 10(-5) M, which could be reversed by the equimolar addition of the receptor agonist 2-chloro-N6-cyclopentyladenosine (P<0.05). The incubation of normal progenitor cells with DPCPX resulted in an inhibition of clonogenic growth to a significantly lesser extent in comparison with CML cells (P<0.05), suggesting that the adenosine A1 receptor is of functional relevance in CML hematopoietic progenitor cells.

A1adenosine receptor knockout mice exhibit increased mortality, renal dysfunction, and hepatic injury in murine septic peritonitis

Sepsis is a leading cause of multiorgan dysfunction and death in hospitalized patients. Dysregulated inflammatory processes and apoptosis contribute to the pathogenesis of sepsis-induced organ dysfunction and death. A(1) adenosine receptor (A(1)AR) activation reduces inflammation and apoptosis after ischemia-reperfusion injury. Therefore, we questioned whether A(1)AR-mediated reduction of inflammation and apoptosis could improve mortality and organ dysfunction in a murine model of sepsis. A(1)AR knockout mice (A(1) knockout) and their wild-type (A(1) wild-type) littermate controls were subjected to cecal ligation and double puncture (CLP) with a 20-gauge needle. A(1) knockout mice or A(1) wild-type mice treated with 1,3-dipropyl-8-cyclopentylxanthine (a selective A(1)AR antagonist) had a significantly higher mortality rate compared with A(1) wild-type mice following CLP. Mice lacking endogenous A(1)ARs demonstrated significant elevations in plasma creatinine, alanine aminotransferase, aspartate aminotransferase, keratinocyte-derived chemokine, and tumor necrosis factor-alpha 24 h after induction of sepsis compared with wild-type mice. The renal corticomedullary junction from A(1) knockout mice also exhibited increased myeloperoxidase activity, intercellular adhesion molecule-1 protein, and mRNA encoding proinflammatory cytokines compared with renal samples from A(1) wild-type littermate controls. No difference in renal tubular apoptosis was detected between A(1) knockout and A(1) wild-type mice. We conclude that endogenous A(1)AR activation confers a protective effect in mice from septic peritonitis primarily by attenuating the hyperacute inflammatory response in sepsis.

New pyrazolo[3,4-b]pyridones as selective A1 adenosine receptor antagonists: synthesis, biological evaluation and molecular modelling studies

A series of ethyl 4-amino-1-(2-chloro-2-phenylethyl)-6-oxo-6,7-dihydro-1H-pyrazolo[3,4-b]pyridine-5-carboxylates () has been synthesized as potential A(1) adenosine receptor (A(1) AR) ligands. Binding affinities of the new compounds were determined for adenosine A(1), A(2A) and A(3) receptors. Compounds and showed good affinity (K(i)= 299 nM and 517 nM, respectively) and selectivity towards A(1) AR, whereas showed good affinity for A(2A) AR (K(i)= 290 nM), higher than towards A(1) AR (K(i)= 1000 nM). The only arylamino derivative of the series displayed high affinity (K(i)= 4.6 nM) and selectivity for A(3) AR. Molecular modelling and 3D-QSAR (CoMFA) studies carried out on the most active compounds gave further support to the pharmacological results.