A3AR Antagonists Research Articles

Caffeine in liver diseases: Pharmacology and toxicology.

We have previously shown that adenosine A1AR antagonists, adenosine A2aAR antagonists, and caffeine have significant inhibitory effects on the activation and proliferation of hepatic stellate cells in alcoholic liver fibrosis. Many recent studies have found that moderate coffee consumption is beneficial for various liver diseases. The main active ingredient of coffee is caffeine, which is a natural non-selective adenosine receptor antagonist. Moreover, numerous preclinical epidemiological studies and clinical trials have examined the association between frequent coffee consumption and the risk of developing different liver diseases. In this review, we summarize and analyze the prophylactic and therapeutic effects of caffeine on various liver diseases, with an emphasis on cellular assays, animal experiments, and clinical trials. To review the prevention and treatment effects of caffeine on different liver diseases, we searched all literature before 19 July 2022, using "caffeine" and "liver disease" as keywords from the PubMed and ScienceDirect databases. We found that moderate coffee consumption has beneficial effects on various liver diseases, possibly by inhibiting adenosine binding to its receptors. Caffeine is a potential drug for the prevention and treatment of various liver diseases.

A1 and A2b adenosine receptors regulate GPX4 against ferroptosis of cardiomyocytes in myocardial infarction rat model and in vitro

AimThe regulation of GPX4 by A1AR and A2bAR was investigated, and whether the inhibition of A1AR and A2bAR on ferroptosis of myocardial cell is related to GPX4 was also discussed. Methodswe constructed a rat model of myocardial ischemia and reperfusion (MIR) model and hypoxia/reoxygenation (H/R) model of H9C2 cells, and MIR rats were intraperitoneally injected with A1AR and A2bAR agonists and antagonists. TTC staining, DHE, TUNEL, western blot experiments, immunohistochemistry assay were implemented to analyze the influence of A1AR and A2bAR on ferroptosis and potential role of GPX4. To further authenticate the result of non-specific agonists and antagonists, we transfected siRNA interference or overexpression vectors into cells. CCK8, flow cytometry and western blot were performed to evaluate cell proliferation and apoptosis, and the expression of GPX4 and ferroptosis-related proteins. ResultsThe experimental results showed that reduced expression of A1AR, A2bAR and GPX4 was found after MIR. A1AR and A2bAR activation by agonists increased GPX4 expression and decreased production of lipid ROS, further inhibiting apoptosis of cardiomyocytes. In addition, we also analyzed the effect of A1AR and A2bAR on ferroptosis-related proteins. We found that expression of FIH1 protein increased and expression of ACSL4 and NOX1 proteins decreased. Consistent with results in vivo, cellular data also indicated that A1AR and A2bAR overexpression could increase proliferation ability of H9C2, and inhibit apoptosis and ROS production, upregulate GPX4 and FIH1, and downregulate ACSL4 and NOX1. ConclusionA1AR and A2bAR could regulate GPX4, thereby affecting ferroptosis of cardiomyocytes in a rat model of MIR.

A3 Adenosine Receptor Antagonists with Nucleoside Structures and Their Anticancer Activity.

The overexpression of the A3 adenosine receptor (AR) in a number of cancer cell types makes it an attractive target for tumor diagnosis and therapy. Hence, in the search for new A3AR ligands, a series of novel 2,N6-disubstituted adenosines (Ados) was synthesized and tested in radioligand binding and functional assays at ARs. Derivatives bearing a 2-phenethylamino group in the N6-position were found to exert higher A3AR affinity and selectivity than the corresponding N6-(2,2-diphenylethyl) analogues. 2-Chloro-N6-phenylethylAdo (15) was found to be a potent full A3AR agonist with a Ki of 0.024 nM and an EC50 of 14 nM, in a cAMP accumulation assay. Unlike 15, the other ligands behaved as A3AR antagonists, which concentration-dependently reduced cell growth and exerted cytostatic activity on the prostate cancer cell line PC3, showing comparable and even more pronounced effects with respect to the ones elicited by the reference full agonist Cl-IB-MECA. In particular, the N6-(2,2-diphenylethyl)-2-phenylethynylAdo (12: GI50 = 14 µM, TGI = 29 µM, and LC50 = 59 µM) showed the highest activity proving to be a potential antitumor agent. The cytostatic effect of both A3AR agonist (Cl-IB-MECA) and antagonists (12 and other newly synthesized compounds) confirm previous observations according to which, in addition to the involvement of A3ARs, other cellular mechanisms are responsible for the anticancer effects of these ligands.

Pharmacological characterization of DPTN and other selective A3 adenosine receptor antagonists.

The A3 adenosine receptor (AR) is emerging as an attractive drug target. Antagonists are proposed for the potential treatment of glaucoma and asthma. However, currently available A3AR antagonists are potent in human and some large animals, but weak or inactive in mouse and rat. In this study, we re-synthesized a previously reported A3AR antagonist, DPTN, and evaluated its affinity and selectivity at human, mouse, and rat ARs. We showed that DPTN, indeed, is a potent A3AR antagonist for all three species tested, albeit a little less selective for mouse and rat A3AR in comparison to the human A3AR. DPTN's Ki values at respective A1, A2A, A2B, and A3 receptors were (nM) 162, 121, 230, and 1.65 (human); 411, 830, 189, and 9.61 (mouse); and 333, 1147, 163, and 8.53 (rat). Its antagonist activity at both human and mouse A3ARs was confirmed in a cyclic AMP functional assay. Considering controversial use of currently commercially available A3AR antagonists in rats and mice, we also re-examined other commonly used and selective A3AR antagonists under the same experimental conditions. The Ki values of MRS1523 were shown to be 43.9, 349, and 216nM at human, mouse, and rat A3ARs, respectively. MRS1191 and MRS1334 showed incomplete inhibition of [125I]I-AB-MECA binding to mouse and rat A3ARs, while potent human A3AR antagonists, MRS1220, MRE3008F20, PSB10, PSB-11, and VUF5574 were largely inactive. Thus, we demonstrated that DPTN and MRS1523 are among the only validated A3AR antagonists that can be possibly used (at an appropriate concentration) in mouse or rat to confirm an A3AR-related mechanism or function.

Dual Actions of A2A and A3 Adenosine Receptor Ligand Prevents Obstruction-Induced Kidney Fibrosis in Mice.

Kidney fibrosis is the final outcome of chronic kidney disease (CKD). Adenosine plays a significant role in protection against cellular damage by activating four subtypes of adenosine receptors (ARs), A1AR, A2AAR, A2BAR, and A3AR. A2AAR agonists protect against inflammation, and A3AR antagonists effectively inhibit the formation of fibrosis. Here, we showed for the first time that LJ-4459, a newly synthesized dual-acting ligand that is an A2AAR agonist and an A3AR antagonist, prevents the progression of tubulointerstitial fibrosis. Unilateral ureteral obstruction (UUO) surgery was performed on 6-week-old male C57BL/6 mice. LJ-4459 (1 and 10 mg/kg) was orally administered for 7 days, started at 1 day before UUO surgery. Pretreatment with LJ-4459 improved kidney morphology and prevented the progression of tubular injury as shown by decreases in urinary kidney injury molecular-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) excretion. Obstruction-induced tubulointerstitial fibrosis was attenuated by LJ-4459, as shown by a decrease in fibrotic protein expression in the kidney. LJ-4459 also inhibited inflammation and oxidative stress in the obstructed kidney, with reduced macrophage infiltration, reduced levels of pro-inflammatory cytokines, as well as reduced levels of reactive oxygen species (ROS). These data demonstrate that LJ-4459 has potential as a therapeutic agent against the progression of tubulointerstitial fibrosis.

New Insights into Key Determinants for Adenosine 1 Receptor Antagonists Selectivity Using Supervised Molecular Dynamics Simulations.

Adenosine receptors (ARs), like many otherGprotein-coupledreceptors (GPCRs), are targets of primary interest indrug design. However, one of the main limits for the development of drugs for this class of GPCRs is the complex selectivity profile usually displayed by ligands. Numerous efforts have been madefor clarifying the selectivity of ARs, leading to the development of many ligand-based models. The structure of the AR subtype A1 (A1AR) has been recently solved, providing important structural insights. In the present work, we rationalized the selectivity profile of two selective A1AR and A2AAR antagonists, investigating their recognition trajectories obtained by Supervised Molecular Dynamics from an unbound state and monitoring the role of the water molecules in the binding site.

Identification of new potent A1 adenosine receptor antagonists using a multistage virtual screening approach

The use of antagonists for each adenosine receptor (AR) subtype as potent clinical candidates is of growing interest due to their involvement in the treatment of various diseases. The recent resolution of several A1 and A2A ARs X-ray structures provides opportunities for structure-based drug design. In this study, we describe the discovery of novel A1AR antagonists by applying a multistage virtual screening approach, which is based on random forest (RF), e-pharmacophore modeling and docking methods. A multistage virtual screening approach was applied to screen the ChemDiv library (1,492,362 compounds). Among the final hits, 22 compounds were selected for further radioligand binding assay analysis against human A1AR, and 18 compounds (81.82% success) exhibited nanomolar or low micromolar binding potency (Ki). Then, we selected six compounds (pKi > 6) to further evaluate their antagonist profile in a cAMP functional assay, and we found that they had low micromolar antagonistic activity (pIC50 = 5.51–6.38) for the A1AR. Particularly, four of six compounds (pKi > 6) showed very good affinity (pKi = 6.11–7.13) and selectively (>100-fold) for A1AR over A2AAR. Moreover, the novelty analysis suggested that four of six compounds (pKi > 6) were dissimilar to existing A1AR antagonists and hence represented novel A1AR antagonists. Further molecular docking and molecular dynamics (MD) studies showed that the three selective compounds 15, 20 and 22 were stabilized (RMSlig value ≤ 2 Å) inside the binding pocket of A1AR with similar orientations to the docking pose in 100-ns MD simulations, whereas they escaped from the binding area of A2AAR with larger values of RMSlig (RMSlig ≥ 2 Å). We hope that these findings provide new insights into the discovery of drugs targeting A1AR and facilitate research on new drugs and treatments for A1AR-related human pathologies.

280-LB: Role of A1 and A3 Adenosine Receptors in Whole Body Glucose Metabolism

A1 and A3 adenosine receptors (ARs) belong to the group of GPCRs that primarily couple to Gi/o protein and mediate adenosine’s biological actions. ARs are widely expressed in the body and regulate various metabolic functions. We generated mice lacking two ARs, Adora1-/-; Adora3-/- (double knockout [A1A3DKO]) to enable investigation of the role of Gi-coupled ARs on glucose metabolism. The Adora1-/- (A1KO), Adora3-/- (A3KO) and WT mice generated as littermates were used as controls. A1A3DKO mice showed no difference in body weight, glucose tolerance, insulin sensitivity, fed blood glucose and plasma insulin levels on regular chow (RC). Fasting blood glucose levels were reduced in A1KO and A1A3DKO mice compared to WT mice. No difference in body weight was observed between A1A3DKO and control groups on high fat diet (HFD). A1KO mice showed improved glucose tolerance compared to A3KO mice without any difference in insulin sensitivity. No difference in plasma insulin levels was observed between the groups. Fasting blood glucose levels were reduced in A1A3DKO mice and A1KO mice compared to WT and A3KO mice, respectively. We investigated the contribution of liver to the observed decrease in fasting blood glucose levels. Pyruvate tolerance test revealed decreased glucose output from the liver in A1KO and A1A3DKO mice. Expression levels of hepatic genes involved in gluconeogenesis, lipid uptake, lipogenesis and inflammation were reduced in A1KO and A1A3DKO mice. Activation of A1AR by specific agonist (MRS7469) increased the phosphorylation of c-Jun N-terminal Kinases (JNK). Increased hepatic glucose production because of Gi signaling-mediated JNK activation is well documented. Taken together, our data support the concept that A1AR antagonists may prove valuable in enhancing whole-body glucose homeostasis by improving hepatic metabolism and could be beneficial in diabetes treatment. Disclosure S. Jain: None. D.K. Tosh: None. M. Reitman: None. K.A. Jacobson: None.

A live cell NanoBRET binding assay allows the study of ligand-binding kinetics to the adenosine A3 receptor

There is a growing interest in understanding the binding kinetics of compounds that bind to G protein-coupled receptors prior to progressing a lead compound into clinical trials. The widely expressed adenosine A3 receptor (A3AR) has been implicated in a range of diseases including immune conditions, and compounds that aim to selectively target this receptor are currently under development for arthritis. Kinetic studies at the A3AR have been performed using a radiolabelled antagonist, but due to the kinetics of this probe, they have been carried out at 10 °C in membrane preparations. In this study, we have developed a live cell NanoBRET ligand binding assay using fluorescent A3AR antagonists to measure kinetic parameters of labelled and unlabelled compounds at the A3AR at physiological temperatures. The kinetic profiles of four fluorescent antagonists were determined in kinetic association assays, and it was found that XAC-ser-tyr-X-BY630 had the longest residence time (RT = 288 ± 62 min) at the A3AR. The association and dissociation rate constants of three antagonists PSB-11, compound 5, and LUF7565 were also determined using two fluorescent ligands (XAC-ser-tyr-X-BY630 or AV039, RT = 6.8 ± 0.8 min) as the labelled probe and compared to those obtained using a radiolabelled antagonist ([3H]PSB-11, RT = 44.6 ± 3.9 min). There was close agreement in the kinetic parameters measured with AV039 and [3H]PSB-11 but significant differences to those obtained using XAC-S-ser-S-tyr-X-BY630. These data indicate that selecting a probe with the appropriate kinetics is important to accurately determine the kinetics of unlabelled ligands with markedly different kinetic profiles.

Correlation study between A3 adenosine receptor binding affinity and anti-renal interstitial fibrosis activity of truncated adenosine derivatives.

Truncated 4'-thionucleosides 1-4 and 4'-oxonucleosides 5-8 as potent and selective A3AR antagonists were synthesized from D-mannose and D-erythronic acid γ-lactone, respectively. These nucleosides were evaluated for their anti-fibrotic renoprotective activity in TGF-β1-treated murine proximal tubular (mProx) cells. Their antagonistic activities for A3AR were proportional to their inhibitory activities against TGF-β1-induced collagen I upregulation in mProx cells. This result suggests that the binding affinity of A3AR antagonists is closely correlated with their anti-fibrotic activity. Thus, A3AR antagonists might be novel therapeutic candidates for treating chronic kidney disease.

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

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

Exploring the Role of N6-Substituents in Potent Dual Acting 5'-C-Ethyltetrazolyladenosine Derivatives: Synthesis, Binding, Functional Assays, and Antinociceptive Effects in Mice ∇.

Structural determinants of affinity of N6-substituted-5'-C-(ethyltetrazol-2-yl)adenosine and 2-chloroadenosine derivatives at adenosine receptor (AR) subtypes were studied with binding and molecular modeling. Small N6-cycloalkyl and 3-halobenzyl groups furnished potent dual acting A1AR agonists and A3AR antagonists. 4 was the most potent dual acting human (h) A1AR agonist (Ki = 0.45 nM) and A3AR antagonist (Ki = 0.31 nM) and highly selective versus A2A; 11 and 26 were most potent at both h and rat (r) A3AR. All N6-substituted-5'-C-(ethyltetrazol-2-yl)adenosine derivatives proved to be antagonists at hA3AR but agonists at the rA3AR. Analgesia of 11, 22, and 26 was evaluated in the mouse formalin test (A3AR antagonist blocked and A3AR agonist strongly potentiated). N6-Methyl-5'-C-(ethyltetrazol-2-yl)adenosine (22) was most potent, inhibiting both phases, as observed combining A1AR and A3AR agonists. This study demonstrated for the first time the advantages of a single molecule activating two AR pathways both leading to benefit in this acute pain model.

Biochemical and Pharmacological Role of A1 Adenosine Receptors and Their Modulation as Novel Therapeutic Strategy.

Adenosine, the purine nucleoside, mediates its effects through activation of four G-protein coupled adenosine receptors (ARs) named as A1, A2A, A2B and A3. In particular, A1ARs are distributed through the body, primarily inhibitory in the regulation of adenylyl cyclase activity and able to reduce the cyclic AMP levels. Considerable advances have been made in the pharmacological and molecular characterization of A1ARs, which had been proposed as targets for the discovery and drug design of antagonists, agonists and allosteric enhancers. Several lines of evidence indicate that adenosine interacting with A1ARs may be an endogenous protective agent in the human body since it prevents the damage caused by various pathological conditions, such as in ischemia/hypoxia, epileptic seizures, excitotoxic neuronal injury and cardiac arrhythmias in cardiovascular system. It has also been reported that one of the most promising targets for the development of new anxiolytic drugs could be A1ARs, and that their activation may reduce pain signaling in the spinal cord. A1AR antagonists induce diuresis and natriuresis in various experimental models, mediating the inhibition of A1ARs in the proximal tubule which is primarily responsible for reabsorption and fluid uptake. In addition, the results of various studies indicate that adenosine is present within pancreatic islets and is implicated through A1ARs in the regulation of insulin secretion and in glucose concentrations. In the present paper it will become apparent that A1ARs could be implicated in the pharmacological treatment of several pathologies with an important influence on human health.

A1 Adenosine Receptor Activation Modulates Central Nervous System Development and Repair.

Adenosine is an endogenous, autacoid purine nucleoside which performs many important biological roles, particularly during stressful events. Adenosine can signal through four adenosine receptor (AR) subtypes: A1, A2A, A2B, and A3. Of these, adenosine A1 receptor (A1AR) has a broad, wide distribution throughout different vertebrate cell types and the highest affinity to adenosine. The A1AR-dependent action of adenosine is well documented in reports from numerous studies that have used different selective A1AR agonists and antagonists as well as in animals that have a genetically manipulated A1AR gene. Despite its wide distribution and function, A1AR homo/hetero-oligomerization with other adenosine and non-adenosine receptors extends its biological role during developmental, physiological, and pathological situations. In this review, we initially discuss the A1AR structure and most important signaling pathway triggered by its activation. Next, we summarize some of the most well-known biological effects of A1AR in the central nervous system (CNS) during development and adulthood, in addition to its role in nervous system regeneration and repair.

Ocular Purine Receptors as Drug Targets in the Eye.

Agonists and antagonists of various subtypes of G protein coupled adenosine receptors (ARs), P2Y receptors (P2YRs), and ATP-gated P2X receptor ion channels (P2XRs) are under consideration as agents for the treatment of ocular diseases, including glaucoma and dry eye. Numerous nucleoside and nonnucleoside modulators of the receptors are available as research tools and potential therapeutic molecules. Three of the 4 subtypes of ARs have been exploited with clinical candidate molecules for treatment of the eye: A1, A2A, and A3. An A1AR agonist is in clinical trials for glaucoma, A2AAR reduces neuroinflammation, A3AR protects retinal ganglion cells from apoptosis, and both A3AR agonists and antagonists had been reported to lower intraocular pressure (IOP). Extracellular concentrations of endogenous nucleotides, including dinucleoside polyphosphates, are increased in pathological states, activating P2Y and P2XRs throughout the eye. P2YR agonists, including P2Y2 and P2Y6, lower IOP. Antagonists of the P2X7R prevent the ATP-induced neuronal apoptosis in the retina. Thus, modulators of the purinome in the eye might be a source of new therapies for ocular diseases.

Pyrazin-2(1H)-ones as a novel class of selective A3 adenosine receptor antagonists.

A3AR antagonists are promising drug candidates as neuroprotective agents as well as for the treatment of inflammation or glaucoma. The most widely known A3AR antagonists are derived from polyheteroaromatic scaffolds, which usually show poor pharmacokinetic properties. Accordingly, the identification of structurally simple A3AR antagonists by the exploration of novel diversity spaces is a challenging goal. A convergent and efficient Ugi-based multicomponent approach enabled the discovery of pyrazin-2(1H)-ones as a novel class of A3AR antagonists. A combined experimental/computational strategy accelerated the establishment of the most salient features of the structure-activity and structure-selectivity relationships in this series. The optimization process provided pyrazin-2(1H)-ones with improved affinity and a plausible hypothesis regarding their binding modes was proposed.

One-pot reaction to obtain N,N'-disubstituted guanidines of pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine scaffold as human A3 adenosine receptor antagonists.

In this paper we describe an extension SAR study of pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine nucleus as A3AR antagonist. Our initial aim was to replace the phenylcarbamoyl moiety at the 5 position of PTP nucleus with a thiourea functionality to evaluate the contribution of new structural modification against the A3AR. The synthesized 12-25 were not characterized by the predicted side chain but by a 1,3-disubstituted guanidine and are shown to be interesting A3AR antagonists.

Involvement of CD73, equilibrative nucleoside transporters and inosine in rhythm and conduction disturbances mediated by adenosine A1 and A2A receptors in the developing heart

We previously established that exogenous adenosine (ADO) induces transient arrhythmias in the developing heart via the adenosine A1 receptor (A1AR) and downstream activation of NADPH oxidase/ERK and PLC/PKC pathways. Here, we investigated the mechanisms by which accumulation of endogenous ADO and its derived compound inosine (INO) in the interstitial compartment induce rhythm and conduction troubles. The validated model of the spontaneously beating heart obtained from 4-day-old chick embryos was used. Quantitative RT-PCR showed that enzymes involved in ADO and INO metabolism (CD39, CD73 and eADA) as well as equilibrative (ENT1, -3, -4) and concentrative (CNT3) nucleoside transporters were differentially expressed in atria, ventricle and outflow tract. Inactivation of ENTs by dipyridamole, 1) increased myocardial ADO level, 2) provoked atrial arrhythmias and atrio-ventricular blocks (AVB) in 70% of the hearts, 3) prolonged P wave and QT interval without altering contractility, and 4) increased ERK2 phosphorylation. Blockade of CD73-mediated phosphohydrolysis of AMP to ADO, MEK/ERK pathway inhibition or A1AR inhibition prevented these arrhythmias. Exposure to exogenous INO also caused atrial ectopy associated with AVB and ERK2 phosphorylation which were prevented by A1AR or A2AAR antagonists exclusively or by MEK/ERK inhibitor. Inhibition of ADA-mediated conversion of ADO to INO increased myocardial ADO and decreased INO as expected, but slightly augmented heart rate variability without provoking AVB. Thus, during cardiogenesis, disturbances of nucleosides metabolism and transport, can lead to interstitial accumulation of ADO and INO and provoke arrhythmias in an autocrine/paracrine manner through A1AR and A2AAR stimulation and ERK2 activation.

Organoruthenium Antagonists of Human A3Adenosine Receptors

Human A₃ adenosine receptor (A₃AR) is a membrane-bound G protein-coupled receptor implicated in a number of severe pathological conditions, including cancer, in which it acts as a potential therapeutic target. To derive structure-activity relationships on pyrazolo-triazolo-pyrimidine (PTP)-based A₃AR antagonists, we developed a new class of organometallic inhibitors through replacement of the triazolo moiety with an organoruthenium fragment. The objective was to introduce by design structural diversity into the PTP scaffold in order to tune their binding efficacy toward the target receptor. These novel organoruthenium antagonists displayed good aquatic stability and moderate binding affinity toward the hA₃ receptor in the low micromolar range. The assembly of these complexes through a template-driven approach with selective ligand replacement at the metal center to control their steric and receptor-binding properties is discussed.

Adenosine A1-receptor knockout mice have a decreased blood pressure response to low-dose ANG II infusion

Adenosine, acting on A(1)-receptors (A(1)-AR) in the nephron, increases sodium reabsorption, and also increases renal vascular resistance (RVR), via A(1)-ARs in the afferent arteriole. ANG II increases blood pressure and RVR, and it stimulates adenosine release in the kidney. We tested the hypothesis that ANG II-infused hypertension is potentiated by A(1)-ARs' influence on Na(+) reabsorption. Mean arterial pressure (MAP) was measured by radiotelemetry in A(1)-AR knockout mice (KO) and their wild-type (WT) controls, before and during ANG II (400 ng·kg(-1)·min(-1)) infusion. Baseline MAP was not different between groups. ANG II increased MAP in both groups, but on day 12, MAP was lower in A(1)-AR KO mice (KO: 128 ± 3 vs. 139 ± 3 mmHg, P < 0.01). Heart rates were significantly different during days 11-14 of ANG II. Basal sodium excretion was not different (KO: 0.15 ± 0.03 vs. WT: 0.13 ± 0.04 mmol/day, not significant) but was higher in KO mice 12 days after ANG II despite a lower MAP (KO: 0.22 ± 0.03 vs. WT: 0.11 ± 0.02 mmol/day, P < 0.05). Phosphate excretion was also higher in A(1)-AR KO mice on day 12. Renal expression of the sodium-dependent phosphate transporter and the Na(+)/glucose cotransporter were lower in the KO mice during ANG II treatment, but the expression of the sodium hydrogen exchanger isoform 3 was not different. These results indicate that the increase in blood pressure seen in A(1)-AR KO mice is lower than that seen in WT mice but was increased by ANG II nonetheless. The presence of A(1)-ARs during a low dose of ANG II-infusion limits Na(+) and phosphate excretion. This study suggests that A(1)-AR antagonists might be an effective antihypertensive agent during ANG II and volume-dependent hypertension.