Identification and characterization of adenosine 5'-tetraphosphate in human myocardial tissue

Migraine signaling pathways: purine metabolites that regulate migraine and predispose migraineurs to headache

Migraine is a debilitating disorder that afflicts over 1 billion people worldwide, involving attacks that result in a throbbing and pulsating headache. Migraine is thought to be a neurovascular event associated with vasoconstriction, vasodilation, and neuronal activation. Understanding signaling in migraine pathology is central to the development of therapeutics for migraine prophylaxis and for mitigation of migraine in the prodrome phase before pain sets in. The fact that both vasoactivity and neural sensitization are involved in migraine indicates that agonists which promote these phenomena may very well be involved in migraine pathology. One such group of agonists is the purines, in particular, adenosine phosphates and their metabolites. This manuscript explores what is known about the relationship between these metabolites and migraine pathology and explores the potential for such relationships through their known signaling pathways. Reported receptor involvement in vasoaction and nociception.

Beyond Triphosphates: Reagents and Methods for Chemical Oligophosphorylation

Oligophosphates play essential roles in biochemistry, and considerable research has been directed toward the synthesis of both naturally occurring oligophosphates and their synthetic analogues. Greater attention has been given to mono-, di-, and triphosphates, as these are present in higher concentrations biologically and easier to synthesize. However, extended oligophosphates have potent biochemical roles, ranging from blood coagulation to HIV drug resistance. Sporadic reports have slowly built a niche body of literature related to the synthesis and study of extended oligophosphates, but newfound interests and developments have the potential to rapidly expand this field. Here we report on current methods to synthesize oligophosphates longer than triphosphates and comment on the most important future directions for this area of research. The state of the art has provided fairly robust methods for synthesizing nucleoside 5'-tetra- and pentaphosphates as well as dinucleoside 5',5'-oligophosphates. Future research should endeavor to push such syntheses to longer oligophosphates while developing synthetic methodologies for rarer morphologies such as 3'-nucleoside oligophosphates, polyphosphates, and phosphonate/thiophosphate analogues of these species.

Several Polyphosphate Kinase 2 Enzymes Catalyse the Production of Adenosine 5'-Polyphosphates

Polyphosphate kinases (PPKs) are involved in many metabolic processes; enzymes of the second family (PPK2) are responsible for nucleotide synthesis fuelled by the consumption of inorganic polyphosphate. They catalyse the phosphorylation of nucleotides with various numbers of phosphate residues, such as monophosphates or diphosphates. Hence, these enzymes are promising candidates for cofactor regeneration systems. Besides adenosine 5'-triphosphate, PPK2s also catalyse the synthesis of highly phosphorylated nucleotides in vitro, as shown here for adenosine 5'-tetraphosphate and adenosine 5'-pentaphosphate. These unusually phosphorylated adenosine 5'-polyphosphates add up to 50 % of the whole adenosine nucleotides in the assay. The two new products were chemically synthesised to serve as standards and compared with the two enzymatically produced compounds by high-performance ion chromatography and ³¹ P NMR analysis. This study shows that PPK2s are highly suitable for biocatalytic synthesis of different phosphorylated nucleotides.

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.

Adenosine 5'-tetraphosphate is a highly potent purinergic endothelium-derived vasoconstrictor

Besides serving as a mechanical barrier, the endothelium has important regulatory functions. The discovery of nitric oxide revolutionized our understanding of vasoregulation. In contrast, the identity of endothelium-derived vasoconstrictive factors still remains uncertain. The supernatant from mechanically stimulated human microvascular endothelial cells elicited a potent vasoconstrictive response in the isolated perfused rat kidney. Whereas a nonselective purinoceptor blocker blocked this vasoactivity most potently, the inhibition of the endothelin receptor by BQ123 weakly affected that vasoconstrictive response. As a compound responsible for that vasoconstrictive effect, we have isolated from HMECs and identified the mononucleotide adenosine 5'-tetraphosphate (AP4). This nucleotide proved to be the most potent vasoactive purinergic mediator identified to date, exerting the vasoconstriction predominantly through activation of the P2X1 receptor. The intraarterial application of AP4 in a Wistar-Kyoto rat induced a strong increase of the mean arterial pressure. The plasma concentration of AP4 is in the nanomolar range, which, in vivo, induces a significant change in the mean arterial pressure. To our knowledge, AP4, which exerts vasoactive effects, is the most potent endogenous mononucleotide identified to date in mammals. The effects of AP4, the plasma concentration of AP4, and its release suggest that this compound functions as an important vasoregulator.

Endogenous coenzyme A glutathione disulfide in human myocardial tissue

Besides its role as a mechanical pump, the human heart serves as an endocrine organ, where known and as yet unknown hormones are produced. It is very likely that these hormones play an important role in cardiovascular regulation. In this study, a new endogenous vasoactive substance, coenzyme A glutathione disulfide (CoASSG), was isolated and identified in myocardial tissue. Human myocardial tissue was extracted with perchloric acid and fractionated by size exclusion-, displacement-, anion-exchange- and reversed-phase chromatography. In one fraction purified to homogeneity, CoASSG was identified by matrix assisted laser desorption/ionization (MALDI) mass-spectrometry, post-source decay MALDI-mass spectrometry and enzymatic structure analysis. Furthermore, CoASSG was also isolated from human cardiac specific granules. CoASSG has potent vasoconstrictive and proliferative effects. Therefore, CoASSG may affect myocardial function as an endocrine or autocrine substance after being released from myocardial specific granules.

Methylene analogues of adenosine 5'-tetraphosphate. Their chemical synthesis and recognition by human and plant mononucleoside tetraphosphatases and dinucleoside tetraphosphatases

Adenosine 5'-polyphosphates have been identified in vitro, as products of certain enzymatic reactions, and in vivo. Although the biological role of these compounds is not known, there exist highly specific hydrolases that degrade nucleoside 5'-polyphosphates into the corresponding nucleoside 5'-triphosphates. One approach to understanding the mechanism and function of these enzymes is through the use of specifically designed phosphonate analogues. We synthesized novel nucleotides: alpha,beta-methylene-adenosine 5'-tetraphosphate (pppCH2pA), beta,gamma-methylene-adenosine 5'-tetraphosphate (ppCH2ppA), gamma,delta-methylene-adenosine 5'-tetraphosphate (pCH2pppA), alphabeta,gammadelta-bismethylene-adenosine 5'-tetraphosphate (pCH2ppCH2pA), alphabeta, betagamma-bismethylene-adenosine 5'-tetraphosphate (ppCH2pCH2pA) and betagamma, gammadelta-bis(dichloro)methylene-adenosine 5'-tetraphosphate (pCCl2pCCl2ppA), and tested them as potential substrates and/or inhibitors of three specific nucleoside tetraphosphatases. In addition, we employed these p4A analogues with two asymmetrically and one symmetrically acting dinucleoside tetraphosphatases. Of the six analogues, only pppCH2pA is a substrate of the two nucleoside tetraphosphatases (EC 3.6.1.14), from yellow lupin seeds and human placenta, and also of the yeast exopolyphosphatase (EC 3.6.1.11). Surprisingly, none of the six analogues inhibited these p4A-hydrolysing enzymes. By contrast, the analogues strongly inhibit the (asymmetrical) dinucleoside tetraphosphatases (EC 3.6.1.17) from human and the narrow-leafed lupin. ppCH2ppA and pCH2pppA, inhibited the human enzyme with Ki values of 1.6 and 2.3 nm, respectively, and the lupin enzyme with Ki values of 30 and 34 nm, respectively. They are thereby identified as being the strongest inhibitors ever reported for the (asymmetrical) dinucleoside tetraphosphatases. The three analogues having two halo/methylene bridges are much less potent inhibitors for these enzymes. These novel nucleotides should prove valuable tools for further studies on the cellular functions of mono- and dinucleoside polyphosphates and on the enzymes involved in their metabolism.

Synthesis of (di)nucleoside polyphosphates by the ubiquitin activating enzyme E1

Previous work from this laboratory had shown that ligases may catalyze the synthesis of (di)nucleoside polyphosphates. Here, we show that one of the enzymes of the proteasome system (E1 or the ubiquitin (Ub) activating enzyme, EC 6.3.2.19) catalyzes very effectively (k(cat) = 0.29+/-0.05 s(-1)) the transfer of AMP from the E-AMP-ubiquitin complex to tripolyphosphate or tetrapolyphosphate with formation of adenosine tetra- or pentaphosphate (p4A or p5A), respectively. Whereas the concomitant formation of AMP is stimulated by the presence of dithiothreitol in a concentration dependent manner, the synthesis of p4A is only slightly inhibited by this compound. Previous treatment of the enzyme (E1) with iodoacetamide inhibited only partially the synthesis of p4A. p4A can substitute for ATP as substrate of the reaction to generate the ubiquityl adenylate complex. A small amount of diadenosine pentaphosphate (Ap5A) was also synthesized in the presence of p4A.

Endothelial cytochrome P450 contributes to the acetylcholine-induced cardiodepression in isolated rat hearts

AIMS

Acetylcholine (ACh) is known to reduce the contractility of the heart by acting on myocardial muscarinic M2 receptors. ACh induces also an endothelial-dependent vasodilatation by causing the release of nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factors from the vascular endothelium. It has been proposed that ACh elicits a hyperpolarization of the coronary endothelial cells which may be accompanied by the activation of cytochrome P450 (CYP) and the resulting release of epoxyeicosatrienoic acids (EETs). The study aims at investigating whether endothelial CYP is involved in the cardiodepression by ACh.

METHODS AND RESULTS

In isolated rat hearts, cardiodepression by ACh (i.e. 25-30% reduction of developed left ventricular pressure) was partially attenuated either by inhibition of CYP with 1-aminobenzotriazole (ABT) or by endothelial dysfunction obtained with Triton X-100. No attenuation of cardiodepression was seen after nitric oxide synthase and cyclooxygenase inhibition by L-nitro-arginine methyl ester and indomethacin, respectively.

CONCLUSION

The results suggest that the negative inotropic effect of ACh depends not only on a direct myocardial effect but also on the endothelial CYP activation.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Adenosine tetraphosphate, Ap4, a physiological regulator of intraocular pressure in normotensive rabbit eyes

Adenosine 5' tetraphosphate, Ap(4), is a natural nucleotide present in many biological systems. This nucleotide has been found as a constituent of the nucleotide pool present in the aqueous humor of New Zealand rabbits. HPLC analysis confirmed its identity and calculated its concentration levels to be 197 +/- 21 nM. When applied topically to the rabbit eyes, this mononucleotide produced a reduction in the intraocular pressure, which was dose-dependent. The pD(2) value calculated from the dose-response curve was 7.28 +/- 0.47, which is equivalent to 52.48 nM. The time course of such intraocular pressure reduction presented a maximal decrease of IOP to 75.1 +/- 2.3% compared with the vehicle control value (100%), and the effect lasted for more than 2 h. Cross-desensitization studies demonstrated that Ap(4) effect was mediated via a P2X receptor in this system. P2 receptor antagonists suramin, pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid (PPADS), and reactive blue 2 (RB-2) showed that only the latter was able to revert the effect of Ap(4). Antagonists of adrenoceptors and cholinoceptors were able to partially reverse the effect of this nucleotide; this might indicate a connection with the neural mechanisms that control the intraocular pressure.