Contractions in human coronary bypass vessels stimulated by extracellular nucleotides

Antegrade cardioplegia as a possible cause of acute saphenous vein endothelial damage in patients undergoing on pump coronary artery bypass surgery

Background

The administration of antegrade cardioplegia through vein grafts after the completion of each distal anastomosis is a common practice. However, the cardioplegic solution may disrupt the vein endothelium and contribute to late vein graft atherosclerotic disease. This study aimed at evaluating the possible impact of the cardioplegic solution on vein graft endothelium.

Methods

Total of 52 patients (16 women and 36 men) aged 68±8.5 years old that underwent on pump coronary revascularization with at least one vein graft were enrolled. Sections of grafts from the greater saphenous vein were obtained prior to and after delivery of potassium antegrade cardioplegic solution through them. These sections were then examined histologically with immunochemical stain and CD34 index. The endothelial damage and length of vein specimens of both graft sections were evaluated.

Results

The endothelial damage of vein specimens appeared to be increased significantly with exposure to antegrade cardioplegia in male and female patients (P from Wilcoxon tests <0.001, for both genders). The increase in the length of vein specimens was significant too (P from Wilcoxon test <0.001 for men and P=0.001 for women).

Conclusions

Antegrade cardioplegia delivered through vein grafts causes substantial damage on vein endothelium. This may have an adverse effect on long-term graft patency.

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.

New insights on pyrimidine signalling within the arterial vasculature - Different roles for P2Y2 and P2Y6 receptors in large and small coronary arteries of the mouse

Extracellular pyrimidines activate P2Y receptors on both smooth muscle cells and endothelial cells, leading to vasoconstriction and relaxation respectively. The aim of this study was to utilize P2Y knock-out (KO) mice to determine which P2Y receptor subtype are responsible for the contraction and relaxation in the coronary circulation and to establish whether P2Y receptors have different functions along the mouse coronary vascular tree. We tested stable pyrimidine analogues on isolated coronary arteries from P2Y2 and P2Y6 receptor KO mice in a myograph setup. In larger diameter segments of the left descending coronary artery (LAD) (lumen diameter~150μm) P2Y6 is the predominant contractile receptor for both UTP (uridine triphosphate) and UDP (uridine diphosphate) induced contraction. In contrast, P2Y2 receptors mediate endothelial-dependent relaxation. However, in smaller diameter LAD segments (lumen diameter~50μm), the situation is opposite, with P2Y2 being the contractile receptor and P2Y6 functioning as a relaxant receptor along with P2Y2. Immunohistochemistry was used to confirm smooth muscle and endothelial localization of the receptors. In vivo measurements of blood pressure in WT mice revealed a biphasic response to the stable analogue UDPβS. Based on the changes in P2Y receptor functionality along the mouse coronary arterial vasculature, we propose that UTP can act as a vasodilator downstream of its release, after being degraded to UDP, without affecting the contractile pyrimidine receptors. We also propose a model, showing physiological relevance for the changes in purinergic receptor functionality along the mouse coronary vascular tree.

Cardiac purinergic signalling in health and disease

This review is a historical account about purinergic signalling in the heart, for readers to see how ideas and understanding have changed as new experimental results were published. Initially, the focus is on the nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory nerves, as well as in intracardiac neurons. Control of the heart by centers in the brain and vagal cardiovascular reflexes involving purines are also discussed. The actions of adenine nucleotides and nucleosides on cardiomyocytes, atrioventricular and sinoatrial nodes, cardiac fibroblasts, and coronary blood vessels are described. Cardiac release and degradation of ATP are also described. Finally, the involvement of purinergic signalling and its therapeutic potential in cardiac pathophysiology is reviewed, including acute and chronic heart failure, ischemia, infarction, arrhythmias, cardiomyopathy, syncope, hypertrophy, coronary artery disease, angina, diabetic cardiomyopathy, as well as heart transplantation and coronary bypass grafts.

Purinergic signaling and blood vessels in health and disease

Purinergic signaling plays important roles in control of vascular tone and remodeling. There is dual control of vascular tone by ATP released as a cotransmitter with noradrenaline from perivascular sympathetic nerves to cause vasoconstriction via P2X1 receptors, whereas ATP released from endothelial cells in response to changes in blood flow (producing shear stress) or hypoxia acts on P2X and P2Y receptors on endothelial cells to produce nitric oxide and endothelium-derived hyperpolarizing factor, which dilates vessels. ATP is also released from sensory-motor nerves during antidromic reflex activity to produce relaxation of some blood vessels. In this review, we stress the differences in neural and endothelial factors in purinergic control of different blood vessels. The long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides in promoting migration and proliferation of both vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis and vessel remodeling during restenosis after angioplasty are described. The pathophysiology of blood vessels and therapeutic potential of purinergic agents in diseases, including hypertension, atherosclerosis, ischemia, thrombosis and stroke, diabetes, and migraine, is discussed.

Translocon closure to Ca2+ leak in proliferating vascular smooth muscle cells

Vascular smooth muscle cells have a proliferative phenotype that is important in vascular development, adaptation, and disease. Intracellular calcium handling is thought to play pivotal roles in determining the properties of these cells, and thus previously unrecognized mechanisms for transmembrane calcium movement are of potential interest. An unsolved question is the mechanism of constitutive (passive) calcium leak from the intracellular stores. Studies of other cell types have suggested that the translocon is a calcium leak pathway. Here we investigated the contribution of the translocon in proliferating vascular smooth muscle cells. Calcium leak into the cytoplasm was measured using fura-2, and protein synthesis was measured using radioactive methionine. Puromycin, emetine, and anisomycin are chemicals that inhibit protein synthesis, acting via the translocon; all three agents strongly inhibited protein synthesis in the smooth muscle cells within 1 h. Puromycin, which opens the translocon, evoked a transient increase in cytoplasmic calcium that was similar in amplitude to the calcium rise evoked by thapsigargin. The puromycin effect was abolished by thapsigargin. The treatment of cells for 1 h with emetine or anisomycin, which close the translocon, inhibited the calcium release evoked by puromycin but not the calcium release evoked by extracellular ATP, endothelin-1, or the calcium ionophore ionomycin. Thapsigargin-evoked calcium rises were slightly suppressed by emetine but unaffected by puromycin or anisomycin. The data suggest that the translocon has the capacity to act as a calcium leak pathway in the ribosomal endoplasmic reticulum but that it is normally closed and lacks relevance to physiological calcium leak mechanisms.

The reversible oral P2Y12 antagonist AZD6140 inhibits ADP-induced contractions in murine and human vasculature

OBJECTIVES

The platelet ADP P2Y(12) receptor which is a target for the antithrombotic drug clopidogrel is also distributed on vascular smooth muscle cells and stimulate contraction. This study investigates whether AZD6140, in contrast to clopidogrel, can inhibit ADP-mediated arterial contractions.

METHODS

Mice were treated with clopidogrel, 50 mg/kg, 24 and 2 h before experiment. Thoracic aorta ring segments from both clopidogrel-treated (n=5) and untreated (n=4) mice were mounted in myograph baths. Contractions of human left internal mammary arteries (IMA) and small arteries were studied in an identical manner.

RESULTS

Clopidogrel treatment per os did not inhibit contractions by the stable ADP analogue 2-MeSADP (10 microM). However, addition of 1 microM AZD6140 in vitro inhibited ADP contraction (% of maximal contraction by 60 mM K(+)) both in the clopidogrel-treated, from 64% to 32% (P=0.002) and in the untreated group, from 59% to 33% (P=0.015). 2-MeSADP contractions in human IMA and small arteries were inhibited by AZD6140.

CONCLUSIONS

The antiplatelet drug AZD6140 blocks the contractile effects of ADP in both murine and human vasculature. These effects of AZD6140 could be beneficial in the management of conditions in which vasospasm may play a role.

Diadenosine polyphosphates are selective vasoconstrictors in human coronary artery bypass grafts

Diadenosine polyphosphates (Ap(n)A) are released by degranulating platelets and high, local concentrations may form at sites of platelet activation. Radial artery grafts, now often used alongside the internal mammary artery in coronary artery bypass surgery, are particularly reactive to several vasoconstrictors but the response to Ap(n)A has not been investigated. This study compared the vasoconstrictor activity of Ap(n)A in human radial artery with other vessels commonly used as bypass grafts. Radial artery demonstrated robust concentration-dependent vasoconstriction to Ap(n)A (n=4-6) at concentrations in the micromolar range. In contrast, average responses in internal mammary artery were negligible. Cross-desensitization revealed that Ap(n)A-mediated vasoconstriction occurred via an alphabetamethyleneATP-sensitive receptor. Responses to both Ap(5)A and alphabetamethyleneATP were inhibited by suramin but were insensitive to the P2X(1) receptor antagonist 8,8'-[Carbonylbis(imino-4,1-phenylenecarbonylimino-4,1-phenylenecarbonylimino)]bis-1,3,5-naphthalenetrisulfonic acid (NF279). Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) enhanced responses to Ap(5)A. Similar responses were obtained in saphenous vein. In conclusion, diadenosine polyphosphates contract radial artery and saphenous vein by an as yet uncharacterized P2X receptor but have only limited activity in internal mammary artery. The selective activity of diadenosine polyphosphates in radial artery would implicate them as potential mediators of post-operative contraction in this graft.

P2 receptors in cardiovascular regulation and disease

The role of ATP as an extracellular signalling molecule is now well established and evidence is accumulating that ATP and other nucleotides (ADP, UTP and UDP) play important roles in cardiovascular physiology and pathophysiology, acting via P2X (ion channel) and P2Y (G protein-coupled) receptors. In this article we consider the dual role of ATP in regulation of vascular tone, released as a cotransmitter from sympathetic nerves or released in the vascular lumen in response to changes in blood flow and hypoxia. Further, purinergic long-term trophic and inflammatory signalling is described in cell proliferation, differentiation, migration and death in angiogenesis, vascular remodelling, restenosis and atherosclerosis. The effects on haemostasis and cardiac regulation is reviewed. The involvement of ATP in vascular diseases such as thrombosis, hypertension and diabetes will also be discussed, as well as various heart conditions. The purinergic system may be of similar importance as the sympathetic and renin-angiotensin-aldosterone systems in cardiovascular regulation and pathophysiology. The extracellular nucleotides and their cardiovascular P2 receptors are now entering the phase of clinical development.

Alterations in Purinoceptor Expression in Human Long Saphenous Vein during Varicose Disease

OBJECTIVES

Varicose veins are dilated tortuous veins of varying tone. Purinergic signalling is important in the control of tone and in mediating trophic changes in blood vessels. The expression of P2 receptors in control and varicose veins will be examined.

METHODS

Purinergic signalling in circular and longitudinal smooth muscle of the human long saphenous vein was studied in control and varicose tissues using immunohistochemistry, organ bath pharmacology and electron microscopy.

RESULTS

P2X1, P2Y1, P2Y2, P2Y4 and P2Y6 receptors were present on circular and longitudinal smooth muscle. Purine-mediated circular and longitudinal muscle contractions were weaker in varicose veins. Electron microscopy and immunohistochemistry findings support the view that smooth muscle cells change from the contractile to synthetic phenotype in varicose veins, associated with an upregulation of P2Y1 and P2Y2 receptors and a down regulation of P2X1 receptors.

CONCLUSIONS

Down regulation of P2X1 receptors on the smooth muscle of varicose veins is associated with loss of contractile activity. Upregulation of P2Y1 and P2Y2 receptors is associated with a shift from contractile to synthetic and/or proliferative roles. The phenotype change in smooth muscle is associated with weakening of vein walls and may be a causal factor in the development of varicose veins.

Pathophysiology and therapeutic potential of purinergic signaling

The concept of a purinergic signaling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief introduction and update of purinoceptor subtypes, this article focuses on the diverse pathophysiological roles of purines and pyrimidines as signaling molecules. These molecules mediate short-term (acute) signaling functions in neurotransmission, mechanosensory transduction, secretion and vasodilatation, and long-term (chronic) signaling functions in cell proliferation, differentiation, and death involved in development and regeneration. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of autonomic cotransmission. Recent advances in therapies using purinergic-related drugs in a wide range of pathological conditions will be addressed with speculation on future developments in the field.

Positive inotropic effects by uridine triphosphate (UTP) and uridine diphosphate (UDP) via P2Y2 and P2Y6 receptors on cardiomyocytes and release of UTP in man during myocardial infarction

The aim of this study was to examine a possible role for extracellular pyrimidines as inotropic factors for the heart. First, nucleotide plasma levels were measured to evaluate whether UTP is released in patients with coronary heart disease. Then, inotropic effects of pyrimidines were examined in isolated mouse cardiomyocytes. Finally, expression of pyrimidine-selective receptors (a subgroup of the P2 receptors) was studied in human and mouse heart, using real time polymerase chain reaction, Western blot, and immunohistochemistry. Venous plasma levels of UTP were increased (57%) in patients with myocardial infarction. In electrically stimulated cardiomyocytes the stable P2Y(2/4) agonist UTPgammaS increased contraction by 52%, similar to beta1-adrenergic stimulation with isoproterenol (65%). The P2Y6-agonist UDPbetaS also increased cardiomyocyte contraction (35%), an effect abolished by the P2Y6-blocker MRS2578. The phospholipase C inhibitor U73122 inhibited both the UDPbetaS and the UTPgammaS-induced inotropic effect, indicating an IP3-mediated effect via P2Y6 receptors. The P2Y14 agonist UDP-glucose was without effect. Quantification of mRNA with real time polymerase chain reaction revealed P2Y2 as the most abundant pyrimidine receptor expressed in cardiomyocytes from man. Presence of P2Y6 receptor mRNA was detected in both species and confirmed at protein level with Western blot and immunohistochemistry in man. In conclusion, UTP levels are increased in humans during myocardial infarction, giving the first evidence for UTP release in man. UTP is a cardiac inotropic factor most likely by activation of P2Y2 receptors in man. For the first time we demonstrate inotropic effects of UDP, mediated by P2Y6 receptors via an IP3-dependent pathway. Thus, the extracellular pyrimidines (UTP and UDP) could be important inotropic factors involved in the development of cardiac disease.

ADP receptor P2Y12 is expressed in vascular smooth muscle cells and stimulates contraction in human blood vessels

OBJECTIVE

ADP plays an important role in platelet aggregation by activating P2Y12 receptors. We assessed the hypothesis that P2Y12 receptors are expressed in vascular smooth muscle cells (VSMC).

METHODS AND RESULTS

P2Y12 receptor mRNA was found to have a high expression among the P2 receptors in human VSMC, significantly higher than the other 2 ADP receptors (P2Y1 and P2Y13, real-time polymerase chain reaction). Western blots gave a band of 50 kD, similar to that in platelets. To unmask a P2Y12 receptor-mediated vasoconstriction by simulating the in vivo situation, vessels were precontracted to a submaximal level. 2-MeSADP stimulated contractions in vessel segments from internal mammary artery (IM), IM branches and small veins (Emax=15+/-6% of 60 mmol/L K+ contraction, pEC50=5.6+/-0.6, Emax=21+/-1%, pEC50=6.8+/-0.1, and Emax=48+/-9%, pEC50=6.6+/-0.4). The selective P2Y12 antagonist AR-C67085 blocked 2-MeSADP contractions. The contraction was not reduced in patients using clopidogrel, a drug inhibiting ADP-induced platelet aggregation by blocking the P2Y12 receptor. This may be explained by the high instability of the active clopidogrel metabolite that never reaches the systemic circulation.

CONCLUSIONS

ADP acting on P2Y12 receptors not only is important for platelet activation but also stimulates vasoconstriction. Stable drugs with antagonistic effects on P2Y12 receptors, affecting both platelets and VSMC, could be of double therapeutic benefit in their prevention of both thrombosis and vasospasm.

P2 receptor mRNA expression profiles in human lymphocytes, monocytes and CD34+ stem and progenitor cells

BACKGROUND

Extracellular nucleotides (ATP, ADP, UTP and UDP) exert a wide range of biological effects in blood cells mediated by multiple ionotropic P2X receptors and G protein-coupled P2Y receptors. Although pharmacological experiments have suggested the presence of several P2 receptor subtypes on monocytes and lymphocytes, some results are contradictory. Few physiological functions have been firmly established to a specific receptor subtype, partly because of a lack of truly selective agonists and antagonists. This stimulated us to investigate the expression of P2X and P2Y receptors in human lymphocytes and monocytes with a newly established quantitative mRNA assay for P2 receptors. In addition, we describe for the first time the expression of P2 receptors in CD34+ stem and progenitor cells implicating a potential role of P2 receptors in hematopoietic lineage and progenitor/stem cell function.

RESULTS

Using a quantitative mRNA assay, we assessed the hypothesis that there are specific P2 receptor profiles in inflammatory cells. The P2X4 receptor had the highest expression in lymphocytes and monocytes. Among the P2Y receptors, P2Y12 and P2Y2 had highest expression in lymphocytes, while the P2Y2 and P2Y13 had highest expression in monocytes. Several P2 receptors were expressed (P2Y2, P2Y1, P2Y12, P2Y13, P2Y11, P2X1, P2X4) in CD34+ stem and progenitor cells.

CONCLUSIONS

The most interesting findings were the high mRNA expression of P2Y12 receptors in lymphocytes potentially explaining the anti-inflammatory effects of clopidogrel, P2Y13 receptors in monocytes and a previously unrecognised expression of P2X4 in lymphocytes and monocytes. In addition, for the first time P2 receptor mRNA expression patterns was studied in CD34+ stem and progenitor cells. Several P2 receptors were expressed (P2Y2, P2Y1, P2Y12, P2Y13, P2Y11, P2X1, P2X4), indicating a role in differentiation and proliferation. Thus, it is possible that specific antibodies to P2 receptors could be used to identify progenitors for monocytes, lymphocytes and megakaryocytes.

Transcriptional down-regulation of the platelet ADP receptor P2Y(12) and clusterin in patients with systemic lupus erythematosus

Cardiovascular complications are common in systemic lupus erythematosus (SLE) and myocardial infarctions are the leading cause of increased mortality. The ADP receptor P2Y(12) plays a central role in platelet activation and the P2Y(12) blocker clopidogrel reduces the incidence of cardiovascular events. Clusterin, a complement inhibitory protein suggested to be involved in the pathogenesis of SLE, has been found recently in a microarray study to be expressed at very high levels in platelets. Using a new protocol for mRNA quantification in platelets we set out to study if gene expression is altered in SLE patients compared with a healthy control group. Quantitative assay based on real-time PCR was used to measure mRNA expression, Western blot for P2 receptor protein expression and PFA-100 for platelet aggregation. The P2Y(12) receptor expression was decreased in SLE compared to the controls (P < 0.05), while expression of P2Y(1) and P2X(1) were unaltered. These findings were consistent at the protein level. The clusterin mRNA expression was very high. However, SLE patients had significantly lower levels than controls (P < 0.05). Platelet aggregation was similar in both groups. It may be suggested that a decreased level of P2Y(12) receptors could represent a protective response in SLE against thrombotic complications. Lowered clusterin levels could be involved in the pathogenesis of SLE due to decreased protective effects. These findings could help to achieve a better understanding of the platelet function in SLE and serve as a guide for further research and drug use.