The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Kathleen M. Giacomini - One of the best experts on this subject based on the ideXlab platform.
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The concentrative Nucleoside transporter family, SLC28
Pflügers Archiv, 2004Co-Authors: Jennifer H. Gray, Ryan P. Owen, Kathleen M. GiacominiAbstract:The SLC28 family consists of three subtypes of sodium-dependent, concentrative Nucleoside transporters, CNT1, CNT2, and CNT3 (SLC28A1, SLC28A2, and SLC28A3, respectively), that transport both naturally occurring Nucleosides and synthetic Nucleoside analogs used in the treatment of various diseases. These subtypes differ in their substrate specificities: CNT1 is pyrimidine-Nucleoside preferring, CNT2 is purine-Nucleoside preferring, and CNT3 transports both pyrimidine and purine Nucleosides. Recent studies have identified key amino acid residues that are determinants of pyrimidine and purine specificity of CNT1 and CNT2. The tissue distributions of the CNTs vary: CNT1 is localized primarily in epithelia, whereas CNT2 and CNT3 have more generalized distributions. Nucleoside transporters in the SLC28 and SLC29 families play critical roles in Nucleoside salvage pathways where they mediate the first step of nucleotide biosynthesis. In addition, these transporters work in concert to terminate adenosine signaling. SLC28 family members are crucial determinants of response to a variety of anticancer and antiviral Nucleoside analogs, as they modulate the entry of these analogs into target tissues. Further, this family is involved in the absorption and disposition of many Nucleoside analogs. Several CNT single Nucleoside polymorphisms (SNPs) have been identified, but have yet to be characterized.
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Nucleoside transporters in the disposition and targeting of Nucleoside analogs in the kidney.
European journal of pharmacology, 2003Co-Authors: Lara M Mangravite, Ilaria Badagnani, Kathleen M. GiacominiAbstract:Systemic disposition of Nucleosides and Nucleoside analogs is dependent on renal handling of these compounds. There are five known, functionally characterized Nucleoside transporters with varying substrate specificities for Nucleosides: concentrative Nucleoside transporters (CNT1-CNT3; Solute Carrier (SLC) 28A1-28A3), which mediate the intracellular flux of Nucleosides, and equilibrative Nucleoside transporters (ENT1-ENT2; SLC29A1-SLC29A2), which mediate bi-directional facilitated diffusion of Nucleosides. All five of these transporters are expressed in the kidney. Concentrative Nucleoside transporters primarily localize to the apical membrane of renal epithelial cells while equilibrative Nucleoside transporters primarily localize to the basolateral membrane. These transporters work in concert to mediate reabsorptive flux of naturally occurring Nucleosides and Nucleoside analogs. In addition, equilibrative transporters also participate in secretory flux of some Nucleoside analogs. Nucleoside transporters also serve in the targeting of Nucleoside analog therapies to renal tumors. This review examines the role that these transporters play in renal disposition of Nucleosides and Nucleoside analogs in both systemic and kidney-specific therapies.
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interaction of Nucleoside analogues with the sodium Nucleoside transport system in brush border membrane vesicles from human kidney
Pharmaceutical Research, 1993Co-Authors: Claire M Brett, Carla B Washington, Marcelo M Gutierrez, Kathleen M. GiacominiAbstract:The therapeutic efficacy of Nucleosides and Nucleoside analogues as antitumor, antiviral, antiparasitic, and antiarrhythmic agents has been well documented. Pharmacokinetic studies suggest that many of these compounds are actively transported in the kidney. The goal of this study was to determine if therapeutically relevant Nucleosides or analogues interact with the recently characterized Na+-driven Nucleoside transport system of the brush border membrane of the human kidney. Brush border membrane vesicles (BBMV) were prepared from human kidney by divalent cation precipitation and differential centrifugation. The initial Na+-driven 3H-uridine uptake into vesicles was determined by rapid filtration. The effect of several naturally occurring Nucleosides (cytidine, thymidine, adenosine), a pyrimidine base (uracil), a nucleotide (UMP), and several synthetic Nucleoside analogues [zidovudine (AZT), cytarabine (Ara-C), and dideoxycytidine (ddC)] on Na+–uridine transport was determined. At a concentration of 100 µM the naturally occurring Nucleosides, uracil, and UMP significantly inhibited Na+-uridine transport, whereas the three synthetic Nucleoside analogues did not. Adenosine competitively inhibited Na+-uridine uptake with a Ki of 26.4 µM (determined by constructing a Dixon plot). These data suggest that naturally occurring Nucleosides are substrates of the Na+–Nucleoside transport system in the renal brush border membrane, whereas synthetic Nucleoside analogues with modifications on the ribose ring are not. The Ki of adenosine is higher than clinically observed concentrations and suggests that the system may play a physiologic role in the disposition of this Nucleoside.
Jose Luis Revuelta - One of the best experts on this subject based on the ideXlab platform.
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Increased production of inosine and guanosine by means of metabolic engineering of the purine pathway in Ashbya gossypii
Microbial Cell Factories, 2015Co-Authors: Rodrigo Ledesma-amaro, Ruben M Buey, Jose Luis RevueltaAbstract:Background Inosine and guanosine monophosphate nucleotides are convenient sources of the umami flavor, with attributed beneficial health effects that have renewed commercial interest in nucleotide fermentations. Accordingly, several bacterial strains that excrete high levels of inosine and guanosine Nucleosides are currently used in the food industry for this purpose. Results In the present study, we show that the filamentous fungus Ashbya gossypii , a natural riboflavin overproducer, excretes high amounts of inosine and guanosine Nucleosides to the culture medium. Following a rational metabolic engineering approach of the de novo purine nucleotide biosynthetic pathway, we increased the excreted levels of inosine up to 27-fold. Conclusions We generated Ashbya gossypii strains with improved production titers of inosine and guanosine. Our results point to Ashbya gossypii as the first eukaryotic microorganism representing a promising candidate, susceptible to further manipulation, for industrial Nucleoside fermentation.
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increased production of inosine and guanosine by means of metabolic engineering of the purine pathway in ashbya gossypii
Microbial Cell Factories, 2015Co-Authors: Rodrigo Ledesmaamaro, Ruben M Buey, Jose Luis RevueltaAbstract:Inosine and guanosine monophosphate nucleotides are convenient sources of the umami flavor, with attributed beneficial health effects that have renewed commercial interest in nucleotide fermentations. Accordingly, several bacterial strains that excrete high levels of inosine and guanosine Nucleosides are currently used in the food industry for this purpose. In the present study, we show that the filamentous fungus Ashbya gossypii, a natural riboflavin overproducer, excretes high amounts of inosine and guanosine Nucleosides to the culture medium. Following a rational metabolic engineering approach of the de novo purine nucleotide biosynthetic pathway, we increased the excreted levels of inosine up to 27-fold. We generated Ashbya gossypii strains with improved production titers of inosine and guanosine. Our results point to Ashbya gossypii as the first eukaryotic microorganism representing a promising candidate, susceptible to further manipulation, for industrial Nucleoside fermentation.
Piero Luigi Ipata - One of the best experts on this subject based on the ideXlab platform.
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Nucleoside recycling in the brain and the nucleosidome: a complex metabolic and molecular cross-talk between the extracellular nucleotide cascade system and the intracellular Nucleoside salvage
Metabolomics, 2015Co-Authors: Piero Luigi Ipata, Rossana PesiAbstract:The transports of Nucleosides from blood into neurons and astrocytes are essential prerequisites to enter their metabolic utilization in brain. Adult brain does not possess the de novo nucleotide synthesis, and maintains its nucleotide pools by salvaging preformed Nucleosides imported from liver. Once Nucleosides enter the brain through the blood brain barrier and the Nucleoside transporters, they become obligatory precursors for the synthesis of RNA and DNA and a plethora of other important functions. However, an aliquot of nucleotides are transferred into vesicular nucleotide transporters, and then in the extracellular space by exocytosis of the vesicles, where ATP and UTP interact with a vast heterogeneity of purine and pyrimidine receptors. Their signal actions are terminated by the ectonucleotidase cascade system, which degrades ATP and UTP into adenosine and uridine, respectively. The low specificity of the vesicular nucleotide transporters may explain the presence in the extracellular space of GTP and CTP, which are equally degraded to their respective Nucleosides by the ectonucleotidases. The main four Nucleosides are re-imported either into the same cell, or in adjacent cells, e.g. between two astrocytes, or between a neuron and an astrocyte, to regenerate Nucleoside triphosphates. The molecular network of this metabolic cross-talk, involving the ectonucleotidases, the Nucleoside transporters, the nucleotide salvage system, the nucleotide transport into the vesicular nucleotide transporters, and the exocytotic release of nucleotides, called by us the “nucleosidome”, serves the Nucleoside recycling in the brain, with a considerable spatial–temporal advantage.
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The Regulation of Brain Nucleoside Utilization
Current Metabolomics, 2014Co-Authors: Piero Luigi Ipata, Francesco BalestriAbstract:The homeostatic regulation of intracellular purine and pyrimidine pools has long been studied at the level of de novo nucleotide synthesis. However, brain maintains the proper qualitative and quantitative nucleotide balance by salvaging preformed Nucleosides, imported from blood stream, rather than by de novo synthesis from simple precursors. The main salvage enzymes are the Nucleoside-kinases, catalyzing the ATP mediated phosphorylation of Nucleosides in their 5’-position. Salvaged Nucleoside-monophosphates are then either further phosphorylated, or converted back to Nucleosides by a set of 5’-nucleotidases. This poses the following problem: why are Nucleosides produced from Nucleosidemonophosphates, to be converted back to the same compounds at the expense of ATP? As discussed in this article, the quantitative and qualitative intracellular balance of brain purine and pyrimidine compounds is maintained i) by the intracellular interplay between the rates of Nucleoside-kinases and 5’-nucleotidases, ii) by the relative rates of the inward and outward Nucleoside transport through equilibrative and concentrative transport systems, iii) by the metabolic cross-talk between extracellularly exported Nucleoside-triphosphate breakdown and the intracellular process of Nucleoside-triphosphate salvage synthesis
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The functional logic of cytosolic 5'-nucleotidases.
Current medicinal chemistry, 2013Co-Authors: Piero Luigi Ipata, Balestri FAbstract:Adenosine- and uridine-cytidine kinases, purine-Nucleoside phosphorylase, hypoxanthine-guanine phosphoribosyl transferase, and several related enzymes, are components of the salvage pathways which reduce the loss of intracellular purine and pyrimidine rings. Although this could explain the role of these enzymes, it poses a problem of the role of the cytosolic 5'-nucleotidase. Why are Nucleosides produced from Nucleoside-monophosphates, only to be converted back to the same compounds? To date, it is well established that a cross talk exists between the extracellular and intracellular Nucleoside metabolism. In districts, such as brain, which are dependent on salvage nucleotide synthesis, Nucleosides are produced through the action of the ecto-5'-nucleotidase, the last component of a series of plasma-membrane bound enzyme proteins, catalyzing the successive dephosphorylation of released Nucleoside-triphosphates. Both Nucleosidetriphosphates (mainly ATP and UTP) and Nucleosides (mainly adenosine), act as extracellular signals. Once transported into cell cytosol, all Nucleosides are salvaged back to Nucleoside-triphosphates, with the exception of inosine, whose salvage is limited to IMP. Intracellular balance of Nucleosides is maintained by the action of several enzymes, such as adenosine deaminase, uridine phosphorylase and cytidine deaminase, and by at least three 5'-nucleotidases, the ADP activated AMP preferring cN-IA, the ATP-ADP activated IMP-GMP preferring cN-II, and the UMP-CMP preferring cN-III. Here we are reviewing the mechanisms whereby cytosolic 5'-nucleotidases control changes in Nucleoside and nucleotide concentration, with the aim to provide a common basis for the study of the relationship between biochemistry and other related disciplines, such as physiology and pharmacology.
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Brain Nucleoside recycling
Metabolomics, 2013Co-Authors: Piero Luigi Ipata, Maria Grazia Tozzi, Francesco Balestri, Marcella CamiciAbstract:The rate limiting reactions of nucleotide synthesis are modulated by intracellular fluctuations of Nucleoside triphosphate concentrations. This topic has been mostly studied at the level of the de novo nucleotide synthesis from simple precursors. However, there are districts, such as brain, which rely more heavily on the salvage of preformed purine and pyrimidine rings, mainly in the form of Nucleosides. This raises the following question: how do these districts maintain the right balance between the purine and pyrimidine pools? We believe that it is now safe to state that a cross talk exists between the extra- and intracellular metabolism of purine and pyrimidine Nucleosides in the brain. The extracellular space is the major site of Nucleoside generation through successive dephosphorylations of released triphosphates, whereas brain cytosol is the major site of multiple phosphorylations of uptaken Nucleosides at their 5′-position. Modulation of both extracellular Nucleoside generation by membrane bound ectonucleotidases, and intracellular Nucleoside phosphorylation by cytosolic kinases might contribute to maintain the right extra- and intracellular purine and pyrimidine nucleotide balance in the brain.
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Metabolic Network of Nucleosides in the Brain
Current topics in medicinal chemistry, 2011Co-Authors: Piero Luigi Ipata, Marcella Camici, Vanna Micheli, Maria Grazia TozziAbstract:Brain relies on circulating Nucleosides, mainly synthesised de novo in the liver, for the synthesis of nucleotides, RNA, nuclear and mitochondrial DNA, coenzymes, and pyrimidine sugar- and lipid-conjugates. Essentially, the paths of Nucleoside salvage in the brain include a two step conversion of inosine and guanosine to IMP and GMP, respectively, and a one step conversion of adenosine, uridine, and cytidine, to AMP, UMP, and CMP, respectively. With the exception of IMP, the other four Nucleoside monophosphates are converted to their respective triphosphates via two successive phosphorylation steps. Brain ribonucleotide reductase converts Nucleoside diphosphates to their deoxy counterparts. The delicate qualitative and quantitative balance of intracellular brain Nucleoside triphosphates is maintained by the relative concentrations of circulating Nucleosides, the specificity and the Km values of the transport systems and of cytosolic and mitochondrial Nucleoside kinases and 5-nucleotidases, and the relative rates of Nucleoside triphosphate extracellular release. A cross talk between extra- and intra-cellular Nucleoside metabolism exists, in which released Nucleoside triphosphates, utilised as neuroactive signals, are catabolised by a membrane bound ectonucleotidase cascade system to their respective Nucleosides, which are uptaken into brain cytosol, and converted back to Nucleoside triphosphates by the salvage enzymes. Finally, phosphorolysis of brain Nucleosides generates pentose phosphates, which are utilised for Nucleoside interconversion, 5-phosphoribosyl-1-pyrophosphate synthesis, and energy repletion. This review focuses on these aspects of brain Nucleoside metabolism, with the aim of giving a comprehensive picture of the metabolic network of Nucleosides in normoxic conditions, with some hints on the derangements in anoxic/ischemic conditions.
James D. Young - One of the best experts on this subject based on the ideXlab platform.
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The SLC28 (CNT) and SLC29 (ENT) Nucleoside transporter families: a 30-year collaborative odyssey
Biochemical Society transactions, 2016Co-Authors: James D. YoungAbstract:Specialized Nucleoside transporter (NT) proteins are required for passage of Nucleosides and hydrophilic Nucleoside analogues across biological membranes. Physiologic Nucleosides serve as central salvage metabolites in nucleotide biosynthesis, and Nucleoside analogues are used as chemotherapeutic agents in the treatment of cancer and antiviral diseases. The Nucleoside adenosine modulates numerous cellular events via purino-receptor cell signalling pathways. Human NTs are divided into two structurally unrelated protein families: the SLC28 concentrative Nucleoside transporter (CNT) family and the SLC29 equilibrative Nucleoside transporter (ENT) family. Human CNTs are inwardly directed Na + -dependent Nucleoside transporters found predominantly in intestinal and renal epithelial and other specialized cell types. Human ENTs mediate bidirectional fluxes of purine and pyrimidine Nucleosides down their concentration gradients and are ubiquitously found in most, possibly all, cell types. Both protein families are evolutionarily old: CNTs are present in both eukaryotes and prokaryotes; ENTs are widely distributed in mammalian, lower vertebrate and other eukaryote species. This mini-review describes a 30-year collaboration with Professor Stephen Baldwin to identify and understand the structures and functions of these physiologically and clinically important transport proteins.
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human equilibrative Nucleoside transporter ent family of Nucleoside and nucleobase transporter proteins
Xenobiotica, 2008Co-Authors: James D. Young, Sylvia Y M Yao, L Sun, C E Cass, S A BaldwinAbstract:1. The human (h) SLC29 family of integral membrane proteins is represented by four members, designated equilibrative Nucleoside transporters (ENTs) because of the properties of the first-characterized family member, hENT1. They belong to the widely distributed eukaryotic ENT family of equilibrative and concentrative Nucleoside/nucleobase transporter proteins. 2. A predicted topology of eleven transmembrane helices has been experimentally confirmed for hENT1. The best-characterized members of the family, hENT1 and hENT2, possess similar broad permeant selectivities for purine and pyrimidine Nucleosides, but hENT2 also efficiently transports nucleobases. hENT3 has a similar broad permeant selectivity for Nucleosides and nucleobases and appears to function in intracellular membranes, including lysosomes. 3. hENT4 is uniquely selective for adenosine, and also transports a variety of organic cations. hENT3 and hENT4 are pH sensitive, and optimally active under acidic conditions. ENTs, including those in parasitic protozoa, function in Nucleoside and nucleobase uptake for salvage pathways of nucleotide synthesis and, in humans, are also responsible for the cellular uptake of Nucleoside analogues used in the treatment of cancers and viral diseases. 4. By regulating the concentration of adenosine available to cell surface receptors, mammalian ENTs additionally influence physiological processes ranging from cardiovascular activity to neurotransmission.
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identification and functional characterization of variants in human concentrative Nucleoside transporter 3 hcnt3 slc28a3 arising from single nucleotide polymorphisms in coding regions of the hcnt3 gene
Pharmacogenetics and Genomics, 2005Co-Authors: Sambasivarao Damaraju, Stephen A. Baldwin, Jing Zhang, Frank Visser, Tracey Tackaberry, Jennifer Dufour, Kyla M Smith, Melissa D Slugoski, Mabel W L Ritzel, James D. YoungAbstract:IntroductionHuman concentrative Nucleoside transporter 3, hCNT3 (SLC28A3), which mediates transport of purine and pyrimidine Nucleosides and a variety of antiviral and anticancer Nucleoside drugs, was investigated to determine if there are single nucleotide polymorphisms in the coding regions of the
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Nucleoside anticancer drugs: the role of Nucleoside transporters in resistance to cancer chemotherapy
Oncogene, 2003Co-Authors: Vijaya L Damaraju, James D. Young, Stephen A. Baldwin, Sambasivarao Damaraju, John Mackey, Michael B Sawyer, Carol E. CassAbstract:The clinical efficacy of anticancer Nucleoside drugs depends on a complex interplay of transporters mediating entry of Nucleoside drugs into cells, efflux mechanisms that remove drugs from intracellular compartments and cellular metabolism to active metabolites. Nucleoside transporters (NTs) are important determinants for salvage of preformed Nucleosides and mediated uptake of antimetabolite Nucleoside drugs into target cells. The focus of this review is the two families of human Nucleoside transporters (hENTs, hCNTs) and their role in transport of cytotoxic chemotherapeutic Nucleoside drugs. Resistance to anticancer Nucleoside drugs is a major clinical problem in which NTs have been implicated. Single nucleotide polymorphisms (SNPs) in drug transporters may contribute to interindividual variation in response to Nucleoside drugs. In this review, we give an overview of the functional and molecular characteristics of human NTs and their potential role in resistance to Nucleoside drugs and discuss the potential use of genetic polymorphism analyses for NTs to address drug resistance.
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Nucleoside transport and its significance for anticancer drug resistance
Drug Resistance Updates, 1998Co-Authors: John R Mackey, James D. Young, Stephen A. Baldwin, Carol E. CassAbstract:Abstract This article discusses the role of Nucleoside transport processes in the cytotoxicity of clinically important anticancer Nucleosides. This article summarizes recent advances in the molecular biology of Nucleoside transport proteins, review the current state of knowledge of the transportability of therapeutically useful anticancer Nucleosides, and provide an overview of the role of Nucleoside transport deficiency as a mechanism of resistance to Nucleoside cytotoxicity are summarized. Several strategies for utilization of Nucleoside transport processes to improve the therapeutic index of anticancer therapies, including the use of Nucleoside-transport inhibitors to modulate toxicity of both Nucleoside and non-Nucleoside antimetabolite drugs are also presented.
Simon M. Jarvis - One of the best experts on this subject based on the ideXlab platform.
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multiple sodium dependent Nucleoside transport systems in bovine renal brush border membrane vesicles
Biochemical Journal, 1991Co-Authors: Timothy C Williams, Simon M. JarvisAbstract:Na(+)-dependent Nucleoside transport was examined in bovine renal brush-border membrane vesicles. Two separate Na+/Nucleoside cotransporters were shown to be present: (1) a system specific for purine Nucleosides and uridine, designated as the N1 carrier, and (2) an Na(+)-dependent Nucleoside transporter that accepts pyrimidine Nucleosides, adenosine and analogues of adenosine, designated as the N2 system. Both systems exhibit a high affinity for Nucleosides (apparent Km values approximately 10 microM), are insensitive to inhibition by facilitated-diffusion Nucleoside transport inhibitors, are rheogenic and exhibit a high specificity for Na+. Na+ increases the affinity of the influx of guanosine and thymidine, Nucleosides that serve as model permeants for the N1 and N2 Nucleoside transporters respectively. The Na+/Nucleoside coupling stoichiometry is consistent with 1:1 for both carriers.
