The role of P2Y6 receptor in the pathogenesis of cardiovascular and inflammatory diseases

The purinergic receptor P2Y6 receptor (P2Y6R) is a member of the G protein-coupled receptors (GPCR) family. P2Y6R is widely expressed in various cell types and plays a critical role in physiological processes, where it is activated by extracellular uridine diphosphate (UDP) and mobilizes Ca2+ via the Gαq/11 protein pathway. We have recently discovered the pathophysiological role of P2Y6R in cardiovascular and inflammatory diseases, including inflammatory bowel disease and non-alcoholic fatty liver disease. Furthermore, we uncovered the redox-dependent internalization of P2Y6R. In this review, we provide a comprehensive overview of the pathophysiological activity of P2Y6R in cardiovascular and inflammatory diseases. Additionally, we discuss the concept of atypical internalization control of GPCRs, which may be applied in the prevention and treatment of intestinal inflammation and cardiovascular remodeling.

Macrophage P2Y6 receptor deletion attenuates atherosclerosis by limiting foam cell formation through phospholipase Cβ/store-operated calcium entry/calreticulin/scavenger receptor A pathways

BACKGROUND AND AIMS

Macrophage-derived foam cells play a causal role during the pathogenesis of atherosclerosis. P2Y6 receptor (P2Y6R) highly expressed has been considered as a disease-causing factor in atherogenesis, but the detailed mechanism remains unknown. This study aims to explore P2Y6R in regulation of macrophage foaming, atherogenesis, and its downstream pathways. Furthermore, the present study sought to find a potent P2Y6R antagonist and investigate the feasibility of P2Y6R-targeting therapy for atherosclerosis.

METHODS

The P2Y6R expression was examined in human atherosclerotic plaques and mouse artery. Atherosclerosis animal models were established in whole-body P2Y6R or macrophage-specific P2Y6R knockout mice to evaluate the role of P2Y6R. RNA sequencing, DNA pull-down experiments, and proteomic approaches were performed to investigate the downstream mechanisms. High-throughput Glide docking pipeline from repurposing drug library was performed to find potent P2Y6R antagonists.

RESULTS

The P2Y6R deficiency alleviated atherogenesis characterized by decreasing plaque formation and lipid deposition of the aorta. Mechanically, deletion of macrophage P2Y6R significantly inhibited uptake of oxidized low-density lipoprotein through decreasing scavenger receptor A expression mediated by phospholipase Cβ/store-operated calcium entry pathways. More importantly, P2Y6R deficiency reduced the binding of scavenger receptor A to CALR, accompanied by dissociation of calreticulin and STIM1. Interestingly, thiamine pyrophosphate was found as a potent P2Y6R antagonist with excellent P2Y6R antagonistic activity and binding affinity, of which the pharmacodynamic effect and mechanism on atherosclerosis were verified.

CONCLUSIONS

Macrophage P2Y6R regulates phospholipase Cβ/store-operated calcium entry/calreticulin signalling pathway to increase scavenger receptor A protein level, thereby improving foam cell formation and atherosclerosis, indicating that the P2Y6R may be a potential therapeutic target for intervention of atherosclerotic diseases using P2Y6R antagonists including thiamine pyrophosphate.

Computational prediction and in vitro analysis of the potential ligand binding site within the extracellular ATP receptor, P2K2

The plant extracellular ATP (eATP) receptor, P2K2, binds eATP with strong ligand affinity through its extracellular lectin domain. Ligand binding activates the intracellular kinase domain of P2K2 resulting in a variety of intracellular responses and, ultimately, increased plant immunity to invading fungal and bacterial pathogens. Here, using a computational prediction approach, we developed a tertiary structure model of the P2K2 extracellular lectin domain. In silico target docking of ATP to the P2K2-binding site predicted interaction with several residues through hydrophobic interactions and hydrogen bonding. Our confirmation of the modeling was obtained by showing that H99, R144, and S256 are key residues essential for in vitro binding of ATP by P2K2.

Tollip deficiency exaggerates airway type 2 inflammation in mice exposed to allergen and influenza A virus: role of the ATP/IL-33 signaling axis

Toll-interacting protein (Tollip) is a negative regulator of the pro-inflammatory response to viruses, including influenza A virus (IAV). Genetic variation of Tollip has been associated with reduced airway epithelial Tollip expression and poor lung function in patients with asthma. Whether Tollip deficiency exaggerates type 2 inflammation (e.g., eosinophils) and viral infection in asthma remains unclear. We sought to address this critical, but unanswered question by using a Tollip deficient mouse asthma model with IAV infection. Further, we determined the underlying mechanisms by focusing on the role of the ATP/IL-33 signaling axis. Wild-type and Tollip KO mice were intranasally exposed to house dust mite (HDM) and IAV with or without inhibitors for IL-33 (i.e., soluble ST2, an IL-33 decoy receptor) and ATP signaling (i.e., an antagonist of the ATP receptor P2Y13). Tollip deficiency amplified airway type 2 inflammation (eosinophils, IL-5, IL-13 and mucins), and the release of ATP and IL-33. Blocking ATP receptor P2Y13 decreased IL-33 release during IAV infection in HDM-challenged Tollip KO mice. Furthermore, soluble ST2 attenuated airway eosinophilic inflammation in Tollip KO mice treated with HDM and IAV. HDM challenges decreased lung viral load in wild-type mice, but Tollip deficiency reduced the protective effects of HDM challenges on viral load. Our data suggests that during IAV infection, Tollip deficiency amplified type 2 inflammation and delayed viral clearance, in part by promoting ATP signaling and subsequent IL-33 release. Our findings may provide several therapeutic targets, including ATP and IL-33 signaling inhibition for attenuating excessive airway type 2 inflammation in human subjects with Tollip deficiency and IAV infection.

Purinergic P2 Receptors: Structure and Function 2.0

This Special Issue of the International Journal of Molecular Sciences (IJMS) is a direct continuation of the previous Special Issue of this journal, entitled “Purinergic P2 Receptors: Structure and Function” https://www [...]

P2Y6 receptor-mediated signaling amplifies TLR-induced pro-inflammatory responses in microglia

TLR-induced signaling initiates inflammatory responses in cells of the innate immune system. These responses are amongst others characterized by the secretion of high levels of pro-inflammatory cytokines, which are tightly regulated and adapted to the microenvironment. Purinergic receptors are powerful modulators of TLR-induced responses, and we here characterized the effects of P2Y6 receptor (P2RY6)-mediated signaling on TLR responses of rhesus macaque primary bone marrow-derived macrophages (BMDM) and microglia, using the selective P2RY6 antagonist MRS2578. We demonstrate that P2RY6-mediated signaling enhances the levels of TLR-induced pro-inflammatory cytokines in microglia in particular. TLR1, 2, 4, 5 and 8-induced responses were all enhanced in microglia, whereas such effects were much less pronounced in BMDM from the same donors. Transcriptome analysis revealed that the overall contribution of P2RY6-mediated signaling to TLR-induced responses in microglia leads to an amplification of pro-inflammatory responses. Detailed target gene analysis predicts that P2RY6-mediated signaling regulates the expression of these genes via modulation of the activity of transcription factors NFAT, IRF and NF-κB. Interestingly, we found that the expression levels of heat shock proteins were strongly induced by inhibition of P2RY6-mediated signaling, both under homeostatic conditions as well as after TLR engagement. Together, our results shed new lights on the specific pro-inflammatory contribution of P2RY6-mediated signaling in neuroinflammation, which might open novel avenues to control brain inflammatory responses.

Aqueous extracts of Urtica dioica (stinging nettle) leaf contain a P2-purinoceptor antagonist—Implications for male fertility

Stinging nettle root and leaf extracts were tested for their effect on prostatic smooth muscle contractility. Root extract did not affect electrical field stimulation induced-nerve mediated contractions of isolated rat prostates. On the other hand, leaf extract attenuated electrical field stimulation-induced contractions at all frequencies. Similarly, contractions elicited by exogenous administration of ATP and αβ-methylene ATP were inhibited by leaf extract, whereas contractions elicited by exogenous administration of noradrenaline or acetylcholine were unaffected. The active component was present within the aqueous phase of the leaf extract. In mouse mating studies, stinging nettle leaf extract (50 mg p.o. daily) reduced male fertility by 53% compared to vehicle-treated male mice. Cardiovascular parameters were unaffected by administration of stinging nettle leaf extract (p ≥ 0.057). Treated mice exhibited normal mating behaviour. Bladder and testes weighed less in stinging nettle leaf extract treated mice. All other organs and total body weight were unaffected. It is concluded that stinging nettle leaf extract reduces contractility of genitourinary smooth muscle by acting as an antagonist at postjunctional P2X1-purinoceptors. These data indicates that blocking sperm transport through pharmacological blockade of P2X1-purinoceptors via oral administration is consistent with an effective and convenient biological strategy male contraception.

Changes in P2Y6 receptor-mediated vasoreactivity following focal and global ischemia

Ischemia, both in the form of focal thromboembolic stroke and following subarachnoid hemorrhage (SAH), causes upregulation of vasoconstrictive receptor systems within the cerebral vasculature. Descriptions regarding changes in purinergic signaling following ischemia are lacking, especially when the importance of purinergic signaling in regulating vascular tone is taken into consideration. This prompted us to evaluate changes in P2Y₆ -mediated vasomotor reactivity in two different stroke models in rat. We used wire myography to measure changes in cerebral vasoreactivity to the P2Y₆ agonist UDP-β-S following either experimental SAH or transient middle cerebral artery occlusion. Changes in receptor localization or receptor expression were evaluated using immunohistochemistry and quantitative flow cytometry. Transient middle cerebral artery occlusion caused an increase in Emax when compared to sham (233.6 [206.1-258.5]% vs. 161.1 [147.1-242.6]%, p = 0.0365). No such change was seen following SAH. Both stroke models were associated with increased levels of P2Y₆ receptor expression in the vascular smooth muscle cells (90.94 [86.99-99.15]% and 93.79 [89.96-96.39]% vs. 80.31 [70.80-80.86]%, p = 0.021) and p = 0.039 respectively. There was no change in receptor localization in either of the stroke models. Based on these findings, we conclude that focal ischemic stroke increases vascular sensitivity to UDP-β-S by upregulating P2Y₆ receptors on vascular smooth muscle cells while experimental SAH did not induce changes in vasoreactivity in spite of increased P2Y₆ receptor expression.

[Involvement of p2 receptors in the contractile activity of the bladder in patients with benign prostatic hyperplasia]

AIM

to study the role of P2 receptors in impaired bladder contractility in patients with lower urinary tract obstruction.

MATERIALS AND METHODS

in pharmacological studies, tissue samples from the bladder wall of 30 patients were used, obtained during planned surgical interventions for benign prostatic hyperplasia (transvesical simple prostatectomy without placement of cystostomy tube). Based on these tissue, isolated smooth muscle specimens were prepared. Their mechanical activity and the efficiency of ligands of purine P2 and other receptors were evaluated. With this aim, the following P2-receptor agonists were used: adenosine triphosphoric acid (ATP), adenosine diphosphoric acid (ADP), uridine-5'-triphosphoric acid (UTP), alpha, beta-methylene-ATP, 2-methylthio-ADP, as well as antagonists of P2-disulfonate receptors acid (PPADS), suramin, NF023, MRS2500. In addition, the efficiency of ligands of other receptors, including carbacholine, epinephrine, histamine, serotonin, atropine was evaluated.

RESULTS

the most effective agonist was alpha-beta-methylene-ATP, while ATP and 2-methylthio-ADP were significantly less active. In our experiments, ADP and UTP did not show an effect on human bladder. The influence of P2 receptor agonists was inhibited by P2 receptor antagonists PPADS and suramin, as well as MRS2500, although to a lesser extent. Carbacholine caused a strong concentration-dependent contractile response of the bladder, which was inhibited by atropine. Histamine resulted in mild bladder contractions only at high concentrations. Epinephrine and serotonin did not cause significant changes in the contractile activity of the bladder.

CONCLUSION

The main subtype of P2 receptors involved in the contractile activity of the human bladder is P2X1 receptors. P2Y1 receptors also have some influence on the contraction, while other subtypes of P2 receptors are not detected by pharmacological methods.

Platelet-rich plasma in umbilical cord blood reduces neuropathic pain in spinal cord injury by altering the expression of ATP receptors

BACKGROUND

Neuropathic pain following injury or dysfunction of the peripheral or CNS is one of the most important medical challenges to treat. Humane platelet-rich plasma (HPRP), which is a rich source of growth factors, may be able to treat and reduce pain caused by spinal cord injury (SCI). In this study, the effect of HPRP on neuropathic pain caused by SCI was investigated.

METHODS

Sixty adult male Wistar rats were randomly divided into 6 groups: control, sham, SCI, vehicle (SCI+platelet-poor plasma), SCI+ PRP2day (injection 48 hrs after SCI) and SCI+PRP14day (injection 14 days after SCI). SCI was induced at the T12-T13 level. Behavioral tests were conducted weekly after injury for six weeks. Allodynia and hyperalgesia were assessed using acetone drops, plantar test and von Frey filament. Cavity size and the number of fibroblasts were determined by H&E stain, and the expression of mTOR, p-mTOR, P₂×₃R and P₂Y₄R were determined using the western blot technique. Data were analyzed using PRISM & SPSS software.

RESULTS

PRP injection showed a higher pain threshold in mechanical allodynia (p<0.0001), cold allodynia (p<0.0001) and thermal hyperalgesia (p<0.0001) than those in the spinal. Animals treated with PRP also reduced cavity size, fibroblast number, p-mTOR/mTOR ratio, and P₂×₃R expression, and increased P₂Y₄R expression. The difference between the two groups was not statistically significant.

CONCLUSIONS

The results showed that PRP reduced SCI-induced allodynia and hyperalgesia by regulating ATP signaling. Using HPRP can open a new window in the treatment of pain caused by damage to the nervous system.

IgE Receptor-Mediated Histamine Release in Human Lung Mast Cells: Modulation by Purinergic Receptor Ligands

BACKGROUND

Mast cells derived from human lungs (HLMCs) express multiple G-protein coupled purinergic receptors (P2YR) and the so-called α-ketoglutarate receptor GPR99, which is homologous to P2YR. The role of the P2YR of HLMC is not clear. Thus, the aim of the present study was to determine the effects of purinergic and purine-related compounds on allergic histamine release (HR) in HLMCs.

METHODS

FcεRI-mediated HR was quantified in primary culture of HLMC (cHLMC). The effects of the FcεRI-mediated allergic stimulation on the expression of GPR99 were also determined.

RESULTS

Adenosine produced a dual effect on HR: enhancement and marked inhibition at low and high concentrations, respectively. Adenosine 5'-monophosphate (AMP) did not affect FcεRI-mediated HR. However, the non-hydrolysable AMP analog, adenosine-5'-O-thiomonophosphate (AMP-S), concentration dependently inhibited the FcεRI-mediated HR without any enhancement. At high concentrations, α-ketoglutarate moderately inhibited FcεRI-mediated HR. However, inhibitions by AMP-S and α-ketoglutarate of HR were dissimilar in the inhibitory manner (IC50 and Hill slope) on histamine release by allergic stimulation.

CONCLUSIONS

cHLMC express functional GPR99 receptor that is up-regulated following allergic stimulation. Responsiveness to AMP-S is the first indication that cHLMC express P2YR, the activation of which can inhibit FcεRI-mediated HR.

A critical look at the function of the P2Y11 receptor

The P2Y11 receptor is a member of the purinergic receptor family. It has been overlooked, somewhat due to the lack of a P2ry11 gene orthologue in the murine genome, which prevents the generation of knockout mice, which have been so helpful for defining the roles of other P2Y receptors. Furthermore, some of the studies reported to date have methodological shortcomings, making it difficult to determine the function of P2Y11 with certainty. In this review, we discuss the lack of a murine "P2Y11-like receptor" and highlight the limitations of the currently available methods used to investigate the P2Y11 receptor. These methods include protein recognition with antibodies that show very little specificity, gene expression studies that completely overlook the existence of a fusion transcript between the adjacent PPAN gene and P2RY11, and agonists/antagonists reported to be specific for the P2Y11 receptor but which have not been tested for activity on numerous other adenosine 5'-triphosphate (ATP)-binding receptors. We suggest a set of criteria for evaluating whether a dataset describes effects mediated by the P2Y11 receptor. Following these criteria, we conclude that the current evidence suggests a role for P2Y11 in immune activation with cell type-specific effects.

[Mechanisms underlying the pathogenesis of neuropathic pain revealing by the role of glial cells]

Injury to the nervous system results in debilitating chronic pain states (called neuropathic pain) whose mechanisms remain unclear. Emerging lines of evidence indicate the pivotal role of spinal glial cells in neuropathic pain. Spinal microglia rapidly respond to peripheral nerve injury (PNI) and become activated with changing expression of a variety of genes. The best known example is purinergic P2X4 receptors, an ATP-gated cation channel. The expression of P2X4 receptors is upregulated in spinal microglia after PNI, and inhibition of P2X4 activity suppresses neuropathic pain. Furthermore, interferon regulatory factor-8 (IRF8) and IRF5 are identified as microglial transcription factors whose expression is upregulated in spinal microglia after PNI, and the IRF8-IRF5 transcriptional cascade is the core process for shifting spinal microglia toward a state with high expression of P2X4 receptors. Astrocytes in the spinal cord show a delayed onset of activation and play an important role in the maintenance of neuropathic pain via the transcription factor STAT3 and the intracellular kinase JNK. These results obtained from glial cell research will advance our understanding of the development and maintenance of neuropathic pain and provide a new target for treating this pain.

Biological effects of leukotriene E4 on eosinophils

Studies demonstrate the existence of novel receptors for cysteinyl leukotrienes (CysLTs) that are responsive to leukotriene (LT) E4 and might be pathogenic in asthma. Given the eosinophilic infiltration in this disorder, we investigated eosinophil expression of P2Y12 and gpr99 and their capacity to respond to LTE4. Receptor transcript expression was investigated via quantitative PCR and surface protein expression via flow cytometry. We investigated LTE4 influences on eosinophils including Ca(+2) flux, cAMP induction, modulation of adhesion molecule expression, apoptosis and degranulation. Eosinophils displayed both transcript and surface protein expression of P2Y12 and gpr99. We could not find evidence of LTE4 activation of eosinophils, however, LTE4 induced cAMP expression, and preincubation of eosinophils with LTE4 inhibited degranulation. Even though eosinophils are an important source of CysLTs in AERD, eosinophils are not themselves the pro-inflammatory biological target and, in contrast, LTE4 via cAMP primarily elicits anti-inflammatory responses.

Isoflurane prevents acute lung injury through ADP-mediated platelet inhibition

BACKGROUND

Growing evidence suggests platelets are essential in posttraumatic, acute lung injury (ALI). Halogenated ethers interfere with the formation of platelet-granulocyte aggregates. The potential benefit of halogenated ethers has not been investigated in models of trauma/hemorrhagic shock (T/HS). Therefore, we hypothesized that isoflurane decreases T/HS-mediated ALI through platelet inhibition.

METHODS

Sprague-Dawley rats (n = 47) were anesthetized by either pentobarbital or inhaled isoflurane and placed into (1) control, (2) trauma (laparotomy) sham shock, (3) T/HS (mean arterial pressure, 30 mmHg × 45 min), (4) pretreatment with an ADP receptor antagonist, or (5) T/HS with isoflurane initiated during resuscitation groups. ALI was determined by protein and pulmonary immunofluorescence bronchoalveolar lavage (BAL) fluid. Platelet Mapping specifically evaluated thrombin-independent inhibition of the ADP and AA pathways of platelet activation.

RESULTS

Pretreatment with isoflurane abrogated ALI as measured by both BAL fluid protein and pulmonary immunofluorescence (P < .001). Platelet Mapping revealed specific inhibition of the platelet ADP-pathway with isoflurane (P < .001). Pretreatment with an ADP receptor antagonist decreased ALI to sham levels, confirming that specific platelet ADP inhibition decreases ALI. Isoflurane initiated during resuscitation also decreased ALI (P < .001).

CONCLUSION

Isoflurane attenuates ALI through an antiplatelet mechanism, in part, through inhibition of the platelet ADP pathway. Isoflurane given postinjury also protects against ALI, and highlights the potential applications of this therapy in various clinical scenarios of ischemia/reperfusion.

Induction of extracellular ATP mediates increase in intracellular thioredoxin in RAW264.7 cells exposed to low-dose γ-rays

We previously showed that low doses (0.25-0.5 Gy) of γ-rays elevated thioredoxin (Trx-1) in various organs of mice after whole-body irradiation. Also, it is reported that extracellular ATP, which is released in response to various stresses, regulates the expression of intracellular antioxidants through activation of P2 receptors. We have recently found that low-dose γ-rays induce ATP release from the exposed cells. However, it is not yet clear whether the radiation-induced extracellular ATP modulates the cellular redox balance. Here, we investigated whether γ-ray irradiation-induced release of extracellular ATP contributes to the induction of the cellular antioxidant Trx-1, using mouse macrophage-like RAW264.7 cells. Irradiation with γ-rays or exogenously added ATP increased the expression of Trx-1, and in both cases the increase was blocked by pretreatment with an ectonucleotidase, apyrase. Then, the involvement of ATP-dependent reactive oxygen species (ROS) generation in the increase in antioxidant capacity was examined. ATP stimulation promoted the generation of intracellular ROS and also increased Trx-1 expression. The increase in Trx-1 expression was significantly suppressed by pretreatment of the cells with antioxidants. In conclusion, the γ-ray irradiation-induced release of extracellular ATP may, at least in part, contribute to the production of ROS via purinergic signaling, leading to promotion of intracellular antioxidants as an adaptive response to an oxidative stress.

Evaluation of the physiological significance of botrocetin/ von Willebrand factor in vitro signaling

BACKGROUND

A signaling pathway is difficult, if not impossible, to elucidate in platelets using only in vivo studies. Likewise, the physiological significance of signaling information obtained exclusively from in vitro observations is unknown. Therefore, both in vitro and in vivo experiments are required to establish the physiological significance of a signaling pathway.

OBJECTIVE

To evaluate the physiological significance of signaling data obtained from botrocetin (bt)/von Willebrand factor (VWF)-stimulated washed platelets.

METHOD

Stable thrombus formation in response to FeCl(3)-induced injury of the mouse carotid artery was used to evaluate the physiological significance of signaling data obtained from bt/VWF-stimulated washed platelets.

RESULTS

Syk, PLCgamma2, Galphaq and P2Y12, but not LAT, were found either to be required for or to affect stable thrombus formation. Prior in vitro studies had demonstrated that LAT is not required for bt/VWF-induced platelet aggregation in the presence of exogenous fibrinogen. These data provide the first demonstration of the in vivo role for these signaling molecules in GPIb-dependent/initiated signal transduction and are consistent with the signaling pathway deduced from in vitro studies of bt/VWF-stimulated washed platelets using metabolic inhibitors and knockout mice.

CONCLUSION

The broad agreement between the in vitro and the in vivo results establish that bt/VWF stimulation of washed platelets can provide physiologically significant glycoprotein Ib-dependent/initiated signaling data.

Synthesis and potency of novel uracil nucleotides and derivatives as P2Y2 and P2Y6 receptor agonists

The phosphate, uracil, and ribose moieties of uracil nucleotides were varied structurally for evaluation of agonist activity at the human P2Y(2), P2Y(4), and P2Y(6) receptors. The 2-thio modification, found previously to enhance P2Y(2) receptor potency, could be combined with other favorable modifications to produce novel molecules that exhibit high potencies and receptor selectivities. Phosphonomethylene bridges introduced for stability in analogues of UDP, UTP, and uracil dinucleotides markedly reduced potency. Truncation of dinucleotide agonists of the P2Y(2) receptor, in the form of Up(4)-sugars, indicated that a terminal uracil ring is not essential for moderate potency at this receptor and that specific SAR patterns are observed at this distal end of the molecule. Key compounds reported in this study include 9, alpha,beta-methylene-UDP, a P2Y(6) receptor agonist; 30, Up(4)-phenyl ester and 34, Up(4)-[1]glucose, selective P2Y(2) receptor agonists; dihalomethylene phosphonate analogues 16 and 41, selective P2Y(2) receptor agonists; 43, the 2-thio analogue of INS37217 (P(1)-(uridine-5')-P(4)-(2'-deoxycytidine-5')tetraphosphate), a potent and selective P2Y(2) receptor agonist.

Challenges in developing P2 purinoceptor-based therapeutics

Advances in the molecular cloning, expression and functional characterization of the P2 purinoceptor superfamily have provided a wealth of data to support a diverse functional role for ATP and related nucleotides in the regulation of tissue function. As with other receptor superfamilies, it is likely that distinct subtypes of each receptor will subserve discrete functions depending on tissue distribution and disease pathophysiology. At the present time, ATP is being evaluated as an anticancer agent and as an anaesthesia adjunct whereas UTP is studied as a novel treatment for cystic fibrosis. ARL67085 is a potent and selective P2T receptor antagonist that has potential as a novel antithrombotic agent. The key to exploiting the P2 purinoceptor area to enhance understanding of disease aetiology and concurrent therapeutic potential will be to focus efforts on the identification of novel pharmacophores that have potent and selective interactions with the various receptor subtypes as potential new leads. To this end, the use of high-throughput screening in conjunction with combinatorial chemical, conventional chemical and natural product library compound sources will be critical.

Both ADP and thrombin regulate arteriolar thrombus stabilization and embolization, but are not involved in initial hemostasis as induced by micropuncture

OBJECTIVE

Thrombosis and embolization are main causes of morbidity and mortality. Up to now, the relative importance of mediators involved is only partly known. It was the aim of this study to investigate the involvement of ADP and thrombin in subsequent phases of arteriolar hemostasis and thromboembolism in vivo.

METHODS

Rabbit mesenteric arterioles were punctured, which induced bleeding, hemostasis, and subsequent thromboembolism. This reaction as well as the activation state of platelets involved ([Ca(2+)](i)), was monitored in real time by intravital (fluorescence) microscopy.

RESULTS

Neither inhibition of thrombin formation or thrombin activity nor blockade of platelet ADP receptors P2Y(1) and P2Y(12) influenced the initial hemostatic reaction: in all experiments initial bleeding was stopped by a primary thrombus within 2-3 s. On the other hand, both thrombin inhibition and P2Y(1) blockade increased rebleeding frequency, which indicates reduced thrombus stability in the long term. Finally, inhibition of either thrombin or ADP (via both receptors) reduced aggregate formation during the embolization phase by at least 90%. While most participating platelets exhibited a transient increase in [Ca(2+)](i) during embolization, an increased percentage of platelets showed no calcium response at all during P2Y(1) blockade, which was accompanied by reduced platelet-platelet interaction strength.

CONCLUSIONS

Whereas thrombin and ADP are not involved in the initial hemostatic reaction, both substances appear to be essential to prevent rebleedings in the long term. During subsequent embolization, ADP (via both receptors) and small amounts of thrombin are involved in platelet activation.

A novel P2Y(12) adenosine diphosphate receptor antagonist that inhibits platelet aggregation and thrombus formation in rat and dog models

Irreversible platelet inhibitors, such as aspirin and clopidogrel, have limited anti-thrombotic efficacy in the clinic due to their bleeding risk. We have developed an orally active reversible P2Y(12) receptor antagonist, BX 667. The aim of this study was to determine if the reversible antagonist BX 667 had a greater therapeutic index than the irreversible P2Y(12) receptor antagonist clopidogrel. Since BX 667 is rapidly converted to its active metabolite BX 048 in rats, we first injected BX 048 intravenously (iv) in a rat arterial venous (A-V) shunt model of thrombosis. BX 048 dose- and concentration-dependently attenuated thrombosis. When administered orally, BX 667 and clopidogrel had similar efficacy, but BX 667 caused less bleeding than clopidogrel. In a rat model of a platelet-rich thrombus induced by vessel injury with FeCl(2), both BX 667 and clopidogrel exhibited higher levels of thrombus inhibition after oral administration compared to their potency in the A-V shunt model. Again, BX 667 caused less bleeding than clopidogrel. In a dog cyclic flow model, iv injection of either BX 667 or clopidogrel dose-dependently reduced thrombus formation with lower bleeding for BX 667 than clopidogrel. Inhibition of thrombosis was highly correlated with inhibition of ADP-induced platelet aggregation in these animal models. In dogs pre-treated with aspirin, BX 667 maintained its wider therapeutic index, measured by inhibition of platelet aggregation over bleeding, compared to the aspirin-clopidogrel combination. These data demonstrate that the reversible P2Y(12) receptor antagonist, BX 667, has a wider therapeutic index than clopidogrel in experimental models of thrombosis.

Structure-activity relationship of uridine 5'-diphosphoglucose analogues as agonists of the human P2Y14 receptor

UDP-glucose (UDPG) and derivatives are naturally occurring agonists of the Gi protein-coupled P2Y14 receptor, which occurs in the immune system. We synthesized and characterized pharmacologically novel analogues of UDPG modified on the nucleobase, ribose, and glucose moieties, as the basis for designing novel ligands in conjunction with modeling. The recombinant human P2Y14 receptor expressed in COS-7 cells was coupled to phospholipase C through an engineered Galpha-q/i protein. Most modifications of the uracil or ribose moieties abolished activity; this is among the least permissive P2Y receptors. However, a 2-thiouracil modification in 15 (EC50 49 +/- 2 nM) enhanced the potency of UDPG (but not UDP-glucuronic acid) by 7-fold. 4-Thio analogue 13 was equipotent to UDPG, but S-alkylation was detrimental. Compound 15 was docked in a rhodposin-based receptor homology model, which correctly predicted potent agonism of UDP-fructose, UDP-mannose, and UDP-inositol. The hexose moiety of UDPG interacts with multiple H-bonding and charged residues and provides a fertile region for agonist modification.

A multiple dose study of prasugrel (CS-747), a novel thienopyridine P2Y12 inhibitor, compared with clopidogrel in healthy humans

AIMS

This double-blind, placebo-controlled trial was designed to evaluate the pharmacodynamics, pharmacokinetics, safety, and tolerability of prasugrel (CS-747, LY640315), a novel thienopyridine P2Y(12) ADP receptor antagonist compared with clopidogrel, during multiple oral dosing in healthy subjects.

METHODS

Thirty subjects received placebo, prasugrel 5 mg, 10 mg, or 20 mg, or clopidogrel 75 mg orally, daily for 10 days. Platelet aggregation, bleeding time, and prasugrel metabolites were measured and adverse events were recorded.

RESULTS

Inhibition of ADP-induced platelet aggregation reached steady state by day 3 following prasugrel 10 and 20 mg compared with 5 days for clopidogrel 75 mg or prasugrel 5 mg. Compared with placebo, at 24 h after the last dose of study drug, inhibition of platelet aggregation using (20 microm) ADP was significantly higher in the prasugrel 10 mg group (58.2 +/- 4.9% vs. 9.2 +/- 4.0%, P < 0.001) with no difference in the clopidogrel group (15.7 +/- 6.8% vs. 9.2 +/- 4.0%, P = 0.78). With 5 microm ADP, inhibition of platelet aggregation with prasugrel 10 mg and clopidogrel 75 mg was significantly higher than with placebo (prasugrel 10 mg, 70.5 +/- 4.7%; clopidogrel 75 mg, 36.5 +/- 9.0%; vs. placebo, 11.3 +/- 5.1%; P < 0.0001 and P = 0.02). On day 10 at 4 h postdose, bleeding time was prolonged with prasugrel 10 mg (prasugrel 10 mg, 706 +/- 252 s vs. placebo, 221 +/- 38 s, P = 0.05) but not with clopidogrel (283 +/- 56 s, P = 0.98). There were no clinically significant bleeding events, serious adverse events, or discontinuations of the study drug.

CONCLUSIONS

Compared with clopidogrel 75 mg, prasugrel 10 mg and 20 mg daily for 10 days resulted in more rapid, more consistent, and higher levels of platelet inhibition.

Synthesis and structure-activity relationships of uracil nucleotide derivatives and analogues as agonists at human P2Y2, P2Y4, and P2Y6 receptors

A series of UTP, UDP, and UMP derivatives and analogues were synthesized and evaluated at the human pyrimidinergic P2Y receptor subtypes P2Y2, P2Y4, and P2Y6 stably expressed in 1321N1 astrocytoma cells. Substituents at N3 of UTP were poorly tolerated by P2Y2 and P2Y4 receptors. In contrast, a large phenacyl substituent at N3 of UDP was well tolerated by the P2Y6 receptor, yielding a potent and selective P2Y6 receptor agonist (3-phenacyl-UDP, EC50=70 nM, >500-fold selective). The most potent and selective P2Y2 receptor agonist of the present series was 2-thio-UTP (EC50=50 nM, >or=30-fold selective vs P2Y4 and P2Y6). All modifications at the uracil base of UTP led to a decrease in potency at the P2Y4 receptor. A beta,gamma-dichloromethylene modification in the triphosphate chain of 5-bromo-UTP was tolerated by all three receptor subtypes, thus opening up a new strategy to obtain ectonucleotide diphosphohydrolase- and phosphatase-resistant P2Y2, P2Y4, and P2Y6 receptor agonists.

Contribution of extracellular signal-regulated kinase to UTP-induced interleukin-6 biosynthesis in HaCaT keratinocytes

UTP causes interleukin (IL)-6 production via mRNA expression through P2Y(2)/P2Y(4) receptors in human HaCaT keratinocytes. In the present study, we analyzed the mechanism of UTP-induced IL-6 production in these cells. UTP, an agonist of P2Y(2)/P2Y(4) receptors, induced phosphorylation of extracellular signal-regulated kinase (ERK) in a concentration- and time-dependent manner. PD98059, a MEK (mitogen-activated protein kinase kinase) inhibitor, and BAPTA-AM [O,O'-bis(2-aminophenyl)ethyleneglycol-N,N,N',N'-tetraacetic acid, tetraacetoxymethyl ester], an intracellular Ca(2+) chelator, reduced UTP-induced ERK phosphorylation and IL-6 mRNA expression. 2-APB [(2-aminoethoxy)diphenylborane], an inositol 1,4,5-trisphosphate (IP(3))-receptor antagonist, inhibited UTP-induced IL-6 mRNA expression; and the action of A23187, a Ca(2+) ionophore, resembled the action of UTP. In contrast, protein kinase C (PKC) downregulation and pertussis toxin did not affect UTP-induced IL-6 mRNA expression, suggesting that PKC and G(i) are not involved in the UTP-induced IL-6 production. However, AG1478, an epidermal growth factor (EGF)-receptor inhibitor, partially decreased UTP-induced ERK phosphorylation and IL-6 expression. These results suggest that UTP-induced IL-6 production is in part mediated via phosphorylation of ERK through G(q/11)/IP(3)/[Ca(2+)](i) and transactivation of the EGF receptor.

[Differential regulation of P2X3 protein expression in the rat trigeminal ganglion after experimental tooth movement]

OBJECTIVE

To investigate the regulation of P2X3 protein expression in the trigeminal ganglion sensory neurons after the nociceptive stimulation by orthodontic tooth movement force.

METHODS

Male Sprague-Dawley rats weighing 200-250 g were used. The mimic tooth movement appliance was used in experimental group rats. The animals were sacrificed after 4 h, 1 d, 2 d, 3 d, 5 d, 7 d and 14 d. The semi-quality of P2X3 protein was measured by Western blot. The expression place and strength of P2X3 was detected by in situ hybridization with an oligonucleotide probe in the same time.

RESULTS

A major specific protein of 4.5 x 10(4) was found by Western blot in trigeminal ganglion of rats. The expression strength of P2X3 receptor increased after given force to the teeth of rats from 1 day of experiment, 3 day group rats showed peak change. 14 day group had returned to control values. The level change of P2X3 mRNA expression showed the same result.

CONCLUSION

The results suggest that the P2X3 receptor expression is transiently upregulated and anterogradely transported in trigeminal primary sensory neurons after orthodontic tooth movement and that P2X3 receptor may play role in the pathomechanism of nociceptive in primary sensory neurons during orthodontic clinic treatment.

Extracellular NAD+ is an agonist of the human P2Y11 purinergic receptor in human granulocytes

Micromolar concentrations of extracellular beta-NAD+ (NAD(e)+) activate human granulocytes (superoxide and NO generation and chemotaxis) by triggering: (i) overproduction of cAMP, (ii) activation of protein kinase A, (iii) stimulation of ADP-ribosyl cyclase and overproduction of cyclic ADP-ribose (cADPR), a universal Ca2+ mobilizer, and (iv) influx of extracellular Ca2+. Here we demonstrate that exposure of granulocytes to millimolar rather than to micromolar NAD(e)+ generates both inositol 1,4,5-trisphosphate (IP3) and cAMP, with a two-step elevation of intracellular calcium levels ([Ca2+]i): a rapid, IP3-mediated Ca2+ release, followed by a sustained influx of extracellular Ca2+ mediated by cADPR. Suramin, an inhibitor of P2Y receptors, abrogated NAD(e)+-induced intracellular increases of IP3, cAMP, cADPR, and [Ca2+]i, suggesting a role for a P2Y receptor coupled to both phospholipase C and adenylyl cyclase. The P2Y(11) receptor is the only known member of the P2Y receptor subfamily coupled to both phospholipase C and adenylyl cyclase. Therefore, we performed experiments on hP2Y(11)-transfected 1321N1 astrocytoma cells: micromolar NAD(e)+ promoted a two-step elevation of the [Ca2+]i due to the enhanced intracellular production of IP3, cAMP, and cADPR in 1321N1-hP2Y(11) but not in untransfected 1321N1 cells. In human granulocytes NF157, a selective and potent inhibitor of P2Y(11), and the down-regulation of P2Y(11) expression by short interference RNA prevented NAD(e)+-induced intracellular increases of [Ca2+]i and chemotaxis. These results demonstrate that beta-NAD(e)+ is an agonist of the P2Y(11) purinoceptor and that P2Y(11) is the endogenous receptor in granulocytes mediating the sustained [Ca2+]i increase responsible for their functional activation.

Plasma ectonucleotidases prevent desensitization of purinergic receptors in stored platelets: importance for platelet activity during thrombus formation

BACKGROUND

Platelets (PLTs) contain purinergic receptors for ATP (P2X1) and ADP (P2Y1 and P2Y12) that rapidly desensitize upon stimulation with these nucleotides. In vivo, this is antagonized by ectonucleotidases on the surface of endothelial cells and white blood cells (WBCs). The receptor desensitization of ATP- and ADP-induced responses of PLTs stored in plasma without WBCs was investigated.

STUDY DESIGN AND METHODS

ATP- and ADP-induced PLT shape change (shear-induced) aggregation and Ca2+ signaling were measured in the presence or absence of plasma. Degradation of nucleotides in plasma was quantified by high-performance liquid chromatography.

RESULTS

Washed PLTs became refractory for ATP and ADP in shape change, aggregation, and Ca2+ responses during a 90-minute incubation at 37 degrees C. The PLT responses mediated by P2X1, P2Y1, and P2Y12 receptors gradually reduced or disappeared. When plasma was present, however, the PLTs persistently showed high responses to ATP and ADP. Heat treatment of plasma abolished this effect. Also under conditions of flow and high shear, PLTs in plasma kept high P2X1 activity, mediating aggregate formation. In isolated plasma, not containing WBCs, nucleotides were degraded in the order of ADP/UDP>ATP/UTP. Degradation of ATP was partly inhibited by blocking the ecto-NTPDase CD39, whereas degradation of both ATP and ADP was inhibited by blocking ectopyrophosphatase/phosphodiesterase activity. Part of the nucleotide-degrading activities appeared to be membrane-bound.

CONCLUSION

Ectonucleotidases in plasma preserve the functionality of P2X1 and P2Y receptors. Upon PLT storage, these plasma activities are essential to ensure adequate (shear-dependent) formation of aggregates and thrombi.

CD21 and CD62L shedding are both inducible via P2X7Rs

Neutrophils and lymphocytes are recruited to sites of inflammation and require the adhesion molecule L-selectin (CD62L) for adherence to endothelial cells. Nucleotides released from activated or dying cells at sites of inflammation can mediate signaling through purinergic receptor family II, resulting in CD62L shedding. Activation of B lymphocytes requires the complement receptor type II (CD21) and at the same time leads to shedding of CD21. Both CD62L and CD21 shedding possibly depends on the same families of proteases. In the present study, we characterized peripheral blood naive and memory cells and neutrophils for CD62L surface expression and analyzed benzoyl-benzoyl triphosphate (BzATP)-induced shedding. BzATP is able to induce CD62L shedding in naive and memory lymphocytes, but not in neutrophils. CD21 shedding can be induced through activation of the B cell receptor (BCR) or with mitogens. Here we show that CD21 is also susceptible to BzATP-induced shedding on peripheral B cells. In addition, using receptor inhibitors, we show that shedding of CD21 and CD62L is mediated via the P2X7R. P2X7R-mediated CD62L and CD21 shedding could occur as a result of extracellular accumulated ATP and may have an influence on leukocyte migrational behavior and BCR-mediated signaling.

P2X7 receptors in the nervous system

P2X(7) receptors are ligand-gated ion channels, expressed as homo-oligomeric assemblies of individual subunits. They are widely distributed at immunocompetent cells of the central and peripheral nervous system and are believed to be primarily involved in host-defense reaction. However, a growing amount of evidence indicates that their signaling role in the brain is more widespread than previously anticipated. In this paper, we review the present knowledge on the structural and pharmacological features of the P2X(7) receptor, as well as its cell-type specific localization in the nervous system. Subsequently, the participation of P2X(7) receptors in distinct neuronal, astroglial and microglial functions are described. Finally, since they may play a prominent role in certain neurologic disorders, such as ischemia-reperfusion injury, Alzheimer's disease, spinal cord injury and sensory neuropathies, the pathological role and potential therapeutic exploitation of P2X(7) receptors are also discussed.

Structure activity and molecular modeling analyses of ribose- and base-modified uridine 5'-triphosphate analogues at the human P2Y2 and P2Y4 receptors

With the long-term goal of developing receptor subtype-selective high affinity agonists for the uracil nucleotide-activated P2Y receptors we have carried out a series of structure activity and molecular modeling studies of the human P2Y2 and P2Y4 receptors. UTP analogues with substitutions in the 2'-position of the ribose moiety retained capacity to activate both P2Y2 and P2Y4 receptors. Certain of these analogues were equieffective for activation of both receptors whereas 2'-amino-2'-deoxy-UTP exhibited higher potency for the P2Y2 receptor and 2'-azido-UTP exhibited higher potency for the P2Y4 receptor. 4-Thio substitution of the uracil base resulted in a UTP analogue with increased potency relative to UTP for activation of both the P2Y2 and P2Y4 receptors. In contrast, 2-thio substitution and halo- or alkyl substitution in the 5-position of the uracil base resulted in molecules that were 3-30-fold more potent at the P2Y2 receptor than P2Y4 receptor. 6-Aza-UTP was a P2Y2 receptor agonist that exhibited no activity at the P2Y4 receptor. Stereoisomers of UTPalphaS and 2'-deoxy-UTPalphaS were more potent at the P2Y2 than P2Y4 receptor, and the R-configuration was favored at both receptors. Molecular docking studies revealed that the binding mode of UTP is similar for both the P2Y2 and P2Y4 receptor binding pockets with the most prominent dissimilarities of the two receptors located in the second transmembrane domain (V90 in the P2Y2 receptor and I92 in the P2Y4 receptor) and the second extracellular loop (T182 in the P2Y2 receptor and L184 in the P2Y4 receptor). In summary, this work reveals substitutions in UTP that differentially affect agonist activity at P2Y2 versus P2Y4 receptors and in combination with molecular modeling studies should lead to chemical synthesis of new receptor subtype-selective drugs.

Adenosine A1 and A2A receptors of hippocampal CA1 region have opposite effects on piriform cortex kindled seizures in rats

In this study the role of adenosine A1 and A2A receptors of the hippocampal CA1 region on piriform cortex-kindled seizures was investigated in rats. Animals were kindled by daily electrical stimulation of piriform cortex. In fully kindled rats, N6-cyclohexyladenosine (CHA; a selective A1 receptor agonist), 1,3-dimethyl-8-cyclopenthylxanthine (CPT; a selective A1 receptor antagonist), CGS21680 hydrochloride (CGS, a selective A2A receptor agonist) and, ZM241385 (ZM, a selective A2A receptor antagonist) were microinfused bilaterally into the hippocampal CA1 region. Rats were stimulated and seizure parameters were measured. Obtained results showed that microinjection of CHA (10 and 100 microM) decreased the afterdischarge duration (ADD), stage 5 seizure duration (S5D) and seizure duration (SD), and significantly increased the latency to stage 4 (S4L). Intra-hippocampal CPT increased ADD at the dose of 20 microM. Pretreatment of rats with CPT (10 microM) before CHA (10 microM), significantly reduced the effect of CHA on seizure parameters. On the other hand, microinjection of CGS (200 and 500 microM) increased ADD, but of ZM had no effect on seizure parameters. Pretreatment of rats with ZM (50 microM) before CGS (500 microM), significantly reduced the effect of CGS on seizure parameters. The results suggest that the facilitatory role of the hippocampal CA1 region in relaying or spreading of piriform cortex kindled seizures is decreased by the activation of adenosine A1 receptors and increased by A2A receptors.

Clopidogrel and ticlopidine: P2Y12 adenosine diphosphate-receptor antagonists for the prevention of atherothrombosis

Ticlopidine and clopidogrel belong to the same chemical family of thienopyridine adenosine diphosphate (ADP)-receptor antagonists. They have shown their efficacy as platelet antiaggregant and antithrombotic agents in many animal models, both ex vivo and in vivo. Although ticlopidine was discovered more than 30 years ago, it was only recently that the mechanism of action of ADP-receptor antagonists was characterized in detail. Ticlopidine and clopidogrel both behave in vivo as specific antagonists of P2Y (12), one of the ADP receptors on platelets. Metabolic steps that involve cytochrome P450-dependent pathways are required to generate the active metabolite responsible for this in vivo activity. The active moiety is a reactive thiol derivative that targets P2Y (12) on platelets. The interaction is irreversible, accounting for the observation that platelets are definitely antiaggregated, even if no active metabolite is detectable in plasma. The interaction is specific for P2Y (12); other purinoceptors such as P2Y (1) and P2Y (13) are spared. This results in inhibition of the binding of the P2Y (12) agonist 2-methylthio-ADP and the ADP-induced downregulation of adenylyl cyclase. Platelet aggregation is affected not only when triggered by ADP but also by aggregation inducers when used at concentrations requiring released ADP as an amplifier. The efficacy and safety of clopidogrel has been established in several large, randomized, controlled trials. The clopidogrel versus aspirin in patients at risk of ischaemic events (CAPRIE) trial demonstrated the superiority of clopidogrel over acetylsalicylic acid (ASA) in patients at risk of ischemic events, including ischemic stroke, myocardial infarction (MI), and peripheral arterial disease. The clopidogrel in unstable angina to prevent recurrent ischemic events (CURE) trial showed a sustained, incremental benefit when clopidogrel was added to standard therapy (including ASA) in patients with unstable angina and non-Q-wave MI. The clopidogrel for the reduction of events during observation (CREDO) trial demonstrated the benefit of continuing clopidogrel (plus ASA) for 12 months, as opposed to 1 month, after percutaneous coronary intervention. The proven efficacy of clopidogrel, coupled with its favorable safety and tolerability profile, has prompted its evaluation in an extensive, ongoing clinical trial program that will help to further characterize the benefit of clopidogrel in patients with a range of atherothrombotic profiles.

Acute effects of glucocorticoids on ATP-induced Ca2+ mobilization and nitric oxide production in cochlear spiral ganglion neurons

Rapid, non-genomic effects of glucocorticoids on extracellular adenosine 5'-triphosphate (ATP)-induced intracellular Ca(2+) concentration ([Ca(2+)](i)) changes and nitric oxide (NO) production were investigated in type I spiral ganglion neurons (SGNs) of the guinea-pig cochlea using the Ca(2+)-sensitive dye fura-2 and the NO-sensitive dye 4,5-diaminofluorescein (DAF-2). Pretreatment of SGNs with 1 microM dexamethasone for 10 min, a synthetic glucocorticoid hormone, enhanced the ATP-induced [Ca(2+)](i) increase in SGNs. RU 38486, a competitive glucocorticoid receptor antagonist eliminated the effects of dexamethasone on the ATP-induced [Ca(2+)](i) increase in SGNs. These acute effects of dexamethasone were dependent on the presence of extracellular Ca(2+), thereby suggesting that dexamethasone may rapidly enhance the Ca(2+) influx through the activation of ionotropic P2X receptors which may interact with glucocorticoid-mediated membrane receptors. Extracellular ATP increased the intensity of DAF-2 fluorescence, indicating NO production in SGNs. The ATP-induced NO production was mainly due to the Ca(2+) influx through the activation of P2 receptors. S-nitroso-N-acetylpenicillamine, a NO donor, enhanced the ATP-induced [Ca(2+)](i) increase in SGNs while L-N(G)-nitroarginine methyl ester (L-NAME), a NO synthesis inhibitor, inhibited it. Dexamethasone enhanced the ATP-induced NO production in SGNs. The augmentation of dexamethasone on ATP-induced NO production was abolished in the presence of l-NAME. It is concluded that the ATP-induced [Ca(2+)](i) increase induces NO production which enhances a [Ca(2+)](i) increase in SGNs by a positive-feedback mechanism. Dexamethasone enhances the ATP-induced [Ca(2+)](i) increase in SGNs which results in the augmentation of NO production. The present study suggests that NO may play an important role in auditory signal transduction. Our results also indicate that glucocorticoids may rapidly affect auditory neurotransmission due to a novel non-genomic mechanism.

Pro- and anti-inflammatory substances modulate expression of the leukotriene B4receptor, BLT1, in human monocytes

The high-affinity leukotriene B(4) (LTB(4)) receptor, BLT1, is a chemotactic receptor involved in inflammatory responses. In this study, we have explored the regulation of BLT1 expression in human monocytes by pro- and anti-inflammatory cytokines, lipopolysaccharide (LPS), and dexamethasone. We found that proinflammatory mediators, such as interferon-gamma (IFN-gamma), tumor necrosis factor-alpha, and LPS, down-regulated expression, whereas the anti-inflammatory cytokine, interleukin-10, and dexamethasone up-regulated BLT1 mRNA expression. The effect of IFN-gamma on BLT1 mRNA expression was rapidly detectable (<4 h) and concentration-dependent (1-50 ng/ml) and seems to be exerted through a block in transcriptional activity. Alterations in mRNA expression were accompanied by changes in BLT1 surface expression, and receptor down-modulation following IFN-gamma stimulation resulted in a diminished chemotactic response to LTB(4). The regulation of BLT1 mRNA and receptor protein expression was similar to the regulation of the monocyte chemoattractant protein-1 chemokine receptor, CC chemokine recptor 2 (CCR2). Flow cytometric analysis of fresh peripheral blood cells revealed that classical (CD14(++)CD16(-)) monocytes express high levels of BLT1 and CCR2 and that both receptors are down-regulated on CD14(+)CD16(+) monocytes. Apart from providing insight into the regulation of BLT1 in human monocytes, our results reveal a parallel expression and regulation of BLT1 and CCR2, which may help to understand monocyte trafficking during pathophysiological conditions.

Positive inotropic and sustained anti-beta-adrenergic effect of diadenosine pentaphosphate in human and guinea pig hearts. Role of dinucleotide receptors and adenosine receptors

AIM

Diadenosine polyphosphates are present intracellularly and in extracellular fluid due to release from secretory vesicles in platelets, chromaffin cells and other cells. This study investigates effects of diadenosine pentaphosphate (AP5A) on heart muscle function.

METHODS

Contractile force amplitude and action potential duration at 90% repolarization (APD90) were measured after challenge with AP5A 50 microm or isoproterenol 50-70 nM in guinea pig papillary muscles. Isoproterenol was given immediately after AP5A-exposure or after 45 min washout. AP5A was combined with antagonists to the purinergic P2 receptor (suramin 100 microm), the dinucleotide receptor [diinosine pentaphosphate 30 microm (IP5I)] or adenosine receptors [8-(P-sulfophenyl) theophylline 50 microm (8-SPT)].

RESULTS

Results are %-change (mean +/- SEM) from value before exposure. AP5A increased contractile force by 22 +/- 3%* (*P <0.05), and IP5I abolished this. AP5A prolonged APD90 by 7 +/- 2%*. AP5A significantly reduced response to isoproterenol acutely from 31 +/- 4* (controls) to 9 +/- 4% and after 45 min washout from 61 +/- 14* (controls) to 16 +/- 5%. 8-SPT abolished the sustained effect. Increase in contractile force by AP5A was confirmed in human atria trabecula preparations.

CONCLUSION

AP5A increased contractile force and prolonged APD90. Contractile force increased by stimulation of the dinucleotide receptor in guinea pig myocardium. The sustained anti-beta-adrenergic effect of AP5A was due to adenosine receptor stimulation.

Purinergic inhibition of the epithelial Na+ transport via hydrolysis of PIP2

Stimulation of purinergic receptors inhibits amiloride-sensitive Na+ transport in epithelial tissues by an unknown mechanism. Because previous studies excluded the role of intracellular Ca2+ or protein kinase C, we examined whether purinergic regulation of Na+ absorption occurs via hydrolysis of phospholipid such as phosphatidylinositol-bisphosphates (PIP2). Inhibition of amiloride-sensitive short-circuit currents (Isc-Amil) by adenine 5'-triphosphate (ATP) in native tracheal epithelia and M1 collecting duct cells was suppressed by binding neomycin to PIP2, and recovery from ATP inhibition was abolished by blocking phosphatidylinositol-4-kinase or diacylglycerol kinase. Stimulation by ATP depleted PIP2 from apical membranes, and PIP2 co-immunoprecipitated the beta subunit of ENaC. ENaC was inhibited by ATP stimulation of P2Y2 receptors in Xenopus oocytes. Mutations in the PIP2 binding domain of betaENaC but not gammaENaC reduced ENaC currents without affecting surface expression. Collectively, these data supply evidence for a novel and physiologically relevant regulation of ENaC in epithelial tissues. Although surface expression is controlled by its C terminus, N-terminal binding of betaENaC to PIP2 determines channel activity.

Diisothiocyanate derivatives as potent, insurmountable antagonists of P2Y6 nucleotide receptors

The physiological role of the P2Y(6) nucleotide receptor may involve cardiovascular, immune and digestive functions based on the receptor tissue distribution, and selective antagonists for this receptor are lacking. We have synthesized a series of symmetric aryl diisothiocyanate derivatives and examined their ability to inhibit phospholipase C (PLC) activity induced by activation of five subtypes of recombinant P2Y receptors. Several derivatives were more potent at inhibiting action of UDP at both human and rat P2Y(6) receptors expressed in 1321N1 human astrocytes than activation of human P2Y(1), P2Y(2), P2Y(4) and P2Y(11) receptors. The inhibition by diisothiocyanate derivatives of 1,2-diphenylethane (MRS2567) and 1,4-di-(phenylthioureido) butane (MRS2578) was concentration-dependent and insurmountable, with IC(50) values of 126+/-15 nM and 37+/-16 nM (human) and 101+/-27 nM and 98+/-11 nM (rat), respectively. A derivative of 1,4-phenylendiisothiocyanate (MRS2575) inhibited only human but not rat P2Y(6) receptor activity. MRS2567 and MRS2578 at 10microM did not affect the UTP (100nM)-induced responses of cells expressing P2Y(2) and P2Y(4) receptors, nor did they affect the 2-methylthio-ADP (30nM)-induced responses at the P2Y(1) receptor or the ATP (10microM)-induced responses at the P2Y(11) receptor. Other antagonists displayed mixed selectivities. The selective antagonists MRS2567, MRS2575 and MRS2578 (1microM) completely blocked the protection by UDP of cells undergoing TNFalpha-induced apoptosis. Thus, we have identified potent, insurmountable antagonists of P2Y(6) receptors that are selective within the family of PLC-coupled P2Y receptors.

Aalpha,beta-methylene ATP enhances P2Y4 contraction of rabbit basilar artery

Interactions between different selective P2 receptor agonists have been used as tools to identify different P2 receptor subtypes. In the present study, we examined the P2 receptor subtypes and the mechanisms of potentiation of UTP contraction (P2Y contraction) by alpha,beta-methylene ATP [(2-carboxypiperazin-4-yl)propyl-1-phosphanoic acid (CPP), a P2X agonist] using isometric tension in the denuded rabbit basilar artery. We made the following observations: 1). a predominant P2X receptor contraction was observed in the rabbit ear artery by the rank order of CPP >> 2-methylthioATP > ATP > UTP; 2). functional P2Y receptors were observed in the rabbit basilar artery by the rank order of UTP >> ATP = CPP = 2-methylthioATP; 3). CPP potentiated UTP-, ATP-, and ATPgammaS-induced contractions, possibly by activation of P2Y4 receptors because ATPgammaS does not activate P2Y6 receptors; and 4). ectonucleotidase did not play a predominant role in the potentiative effect of CPP because Evans blue, Ca(2+)-free medium, or divalent cation Ni(2+) did not affect the effect of CPP. Evans blue potentiated the contraction by UTP but not by ATP or ATPgammaS. We conclude that CPP enhanced P2Y4-mediated contraction in the rabbit basilar artery, and the influence by ectonucleotidases on CPP-potentiation remains unclear.

2-Alkylthio-substituted platelet P2Y12 receptor antagonists reveal pharmacological identity between the rat brain Gi-linked ADP receptors and P2Y12

The Gi-linked platelet ADP receptor, now designated as P2Y12, accounts for ADP-induced inhibition of adenylyl cyclase in platelets and certain clonal rat cell lines. The pharmacology of this receptor is well characterized. Based on the functional approach of [35S]GTPgammaS autoradiography, we recently disclosed the widespread presence of Gi-linked ADP receptors in the rat nervous system. Based on initial pharmacological analysis, these receptors were strikingly similar with P2Y12. Here, we extend this analysis by comparing the potencies of six 2-alkylthio-substituted ATP analogues, including the adenosine-aspartate conjugate 2-hexylthio-AdoOC(O)Asp2 and five AR-C compounds (AR-C67085, AR-C69931, AR-C78511, AR-C69581, AR-C70300) with wide range of affinities towards P2Y12, in reversing 2-methylthio-ADP stimulated G protein activity in rat brain sections and human platelet membranes. Closely matching pIC50 values (r2=0.99) revealed pharmacological similarity between the two receptors with one exception: AR-C67085 more avidly recognized the platelet P2Y12. Further analysis of the rat brain pIC50 data against those available for three of the AR-C compounds in reversing P2Y12-mediated adenylyl cyclase inhibition in rat platelets (r2=0.96) and rat C6 glioma cells (r2=1.00) demonstrated that the three P2Y receptors are pharmacologically indistinguishable. We conclude that the rat brain Gi-linked ADP receptors, as revealed using [35S]GTPgammaS autoradiography, correspond to P2Y12.

Third-generation beta-blockers stimulate nitric oxide release from endothelial cells through ATP efflux: a novel mechanism for antihypertensive action

BACKGROUND

Nebivolol and carvedilol are third-generation beta-adrenoreceptor antagonists, which unlike classic beta-blockers, have additional endothelium-dependent vasodilating properties specifically related to microcirculation by a molecular mechanism that still remains unclear. We hypothesized that nebivolol and carvedilol stimulate NO release from microvascular endothelial cells by extracellular ATP, which is a well-established potent autocrine and paracrine signaling factor modulating a variety of cellular functions through the activation of P2-purinoceptors.

METHODS AND RESULTS

Contraction and relaxation of renal glomerular vasculature were measured by determination of intracapillary volume with [3H]-inulin. Biologically active NO was measured with highly sensitive porphyrinic NO microsensors in a single glomerular endothelial cell (GEC). Extracellular ATP was measured by a luciferin-luciferase assay. Enzymatic degradation of extracellular ATP by apyrase and blockade of P2Y-purinoceptors by suramin or reactive blue 2 inhibited both beta-blocker-induced glomerular vasorelaxations and beta-blocker-stimulated NO release from GECs. Both beta-blocker-induced vasorelaxations were in the micromolar concentration range identical to that required for the beta-blocker stimulation of ATP and NO release from GECs. The maximum of NO release for nebivolol and carvedilol was very similar (188+/-14 and 226+/-17, respectively). Blockade of ATP release by a mechanosensitive ion channel blocker, Gd3+, inhibited the beta-blocker-dependent release of ATP and NO from GECs.

CONCLUSIONS

These results demonstrate for the first time that nebivolol and carvedilol induce relaxation of renal glomerular microvasculature through ATP efflux with consequent stimulation of P2Y-purinoceptor-mediated NO release from GECs.

Thrombin-induced platelet PAR4 activation: role of glycoprotein Ib and ADP

Thrombin activates human platelets via the cleavage of two protease-activated G-protein coupled receptors (PARs), PAR1 and PAR4 that respond to low and high concentrations of thrombin, respectively. The aim of the present study was to examine the relative contributions of GPIbalpha and ADP receptors in response to thrombin-induced PAR1 and PAR4 stimulation. Platelet responses (aggregation, secretion and calcium mobilization) elicited by low thrombin concentrations were impaired when thrombin interaction with GPIbalpha was blocked. In contrast, blockade of thrombin interaction with GPIbalpha had no effect when PAR4-coupled responses were specifically elicited by high thrombin concentrations in the presence of PAR1 antagonists or after PAR1 desensitization. These results confirmed that unlike PAR1, PAR4 does not require GPIbalpha as a cofactor for thrombin-mediated activation. Both apyrase and selective antagonists of P2Y1 and P2Y12 inhibited PAR1-coupled responses but did not modify PAR4-coupled responses, indicating that in contrast to PAR1, PAR4 signals are not reinforced by ADP secretion and binding to the platelets. These results provide the direct evidence that, in human platelets, GPIbalpha and ADP act in synergy to amplify PAR1 coupled responses while PAR4 is activated independently of GPIbalpha and ADP.

Selective labeling of zebrafish thrombocytes: quantitation of thrombocyte function and detection during development

Zebrafish thrombocytes, the nucleated equivalents of mammalian platelets, have been characterized morphologically, but knowledge about their developmental synthesis and biochemistry is limited. Given the increasing use of zebrafish as a genetic model to study hemostasis, it is important to isolate and study the function of zebrafish thrombocytes. Therefore, the objective of this study was to isolate thrombocytes, study their function in vitro, and identify the developmental stage at which they enter circulation. To achieve these goals, we developed a method for the selective labeling of thrombocytes and assayed these cells for activation by known mammalian platelet agonists. In both in vitro incubations of whole blood and blood labeled in vivo with the lipophilic dye DiI-C(18), we found labeling in only a single population of cells. These cells were identified as zebrafish thrombocytes by Wright-Giemsa staining. Using selective DiI-C(18) labeling, we showed the formation of thrombocyte aggregates, filopodia, and lipid rafts in response to platelet agonists. Additionally, we showed that aggregates are labeled by binding FITC-conjugated annexin V to exposed phosphatidylserine on the thrombocyte membrane. Using these fluorescent-labeling methods, we developed the first microquantitative assay for thrombocyte aggregation. With this assay, we provided evidence for the presence of an ADP receptor, P2Y(1), in the zebrafish thrombocytes. To study the developmental stage at which thrombocytes appear, we microinjected DiI-C(18) into the circulation of zebrafish embryos and identified the presence of DiI-C(18)-labeled thrombocytes at the 36 h postfertilization stage. These findings will prove helpful in dissecting the functions of thrombocytes in hemostasis and provide further insight into the role of platelets in thrombosis.