Nucleoside Transport. II. Inhibition by p-Nitrobenzylthioguanosine and Related Compounds

1971 ◽  
Vol 49 (2) ◽  
pp. 271-274 ◽  
Author(s):  
A. R. P. Paterson ◽  
J. M. Oliver
Keyword(s):  
Potent Inhibitor ◽  
Facilitated Transport ◽  
Human Erythrocytes ◽  
Nucleoside Transport ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Uridine Uptake ◽  
Related Compounds

p-Nitrobenzylthioguanosine (NBTGR) was found to be a potent inhibitor of nucleoside transport by human erythrocytes; initial rates of uridine uptake were reduced to zero upon exposure of cells to 10−6 M NBTGR. The inhibitor was firmly bound because repeated washing did not restore uridine transport capability to NBTGR-treated cells. NBTGR inhibited the influx of uridine, inosine, and cytidine, without inhibiting the uptake of the corresponding bases, or that of D-glucose or L-leucine. Uridine antagonized the NBTGR inhibition of uridine transport in a concentration-dependent manner. NBTGR and related compounds appear to interact with the mechanism for the facilitated transport of nucleosides.

scholarly journals Nucleoside uptake in rat liver parenchymal cells

1996 ◽  
Vol 317 (3) ◽  
pp. 835-842 ◽  
Author(s):  
Joan MERCADER ◽  
Mireia GOMEZ-ANGELATS ◽  
Belén del SANTO ◽  
Javier CASADO ◽  
Antonio F. FELIPE ◽  
...  
Keyword(s):  
Rat Liver ◽  
Nucleoside Transport ◽  
Transport Systems ◽  
Dependent Manner ◽  
Transport Activity ◽  
Liver Parenchymal ◽  
Uridine Uptake ◽  
High Concentrations ◽  
Parenchymal Cells ◽  
Dose Dependent

Rat liver parenchymal cells express Na+-dependent and Na+-independent nucleoside transport activity. The Na+-dependent component shows kinetic properties and substrate specificity similar to those reported for plasma membrane vesicles [Ruiz-Montasell, Casado, Felipe and Pastor-Anglada (1992) J. Membr. Biol. 128, 227–233]. This transport activity shows apparent Km values for uridine in the range 8–13 μM and a Vmax of 246 pmol of uridine per 3 min per 106 cells. Most nucleosides, including the analogue formycin B, cis-inhibit Na+-dependent uridine transport, although thymidine and cytidine are poor inhibitors. Inosine and adenosine inhibit Na+-dependent uridine uptake in a dose-dependent manner, reaching total inhibition. Guanosine also inhibits Na+-dependent uridine uptake, although there is some residual transport activity (35% of the control values) that is resistant to high concentrations of guanosine but may be inhibited by low concentrations of adenosine. The transport activity that is inhibited by high concentrations of thymidine is similar to the guanosine-resistant fraction. These observations are consistent with the presence of at least two Na+-dependent transport systems. Na+-dependent uridine uptake is sensitive to N-ethylmaleimide treatment, but Na+-independent transport is not. Nitrobenzylthioinosine (NBTI) stimulates Na+-dependent uridine uptake. The NBTI effect involves a change in Vmax, it is rapid, dose-dependent, does not need preincubation and can be abolished by depleting the Na+ transmembrane electrochemical gradient. Na+-independent uridine transport seems to be insensitive to NBTI. Under the same experimental conditions, NBTI effectively blocks most of the Na+-independent uridine uptake in hepatoma cells. Thus the stimulatory effect of NBTI on the concentrative nucleoside transporter of liver parenchymal cells cannot be explained by inhibition of nucleoside efflux.

The cytoprotective effects of bilirubin and biliverdin on rat hepatocytes and human erythrocytes and the impact of albumin

1991 ◽  
Vol 69 (12) ◽  
pp. 828-834 ◽  
Author(s):  
Tai-Wing Wu ◽  
Doug Carey ◽  
Jun Wu ◽  
Hiroshi Sugiyama
Keyword(s):  
Rat Hepatocytes ◽  
Human Erythrocytes ◽  
Red Cells ◽  
Peroxyl Radicals ◽  
Blood Levels ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Hepatocyte Necrosis ◽  
The Impact ◽  
First Time

The hypothesis that unconjugated bilirubin and biliverdin are cytoprotective antioxidants has been examined for the first time in systems containing cells. In primary rat hepatocytes exposed to xanthine oxidase and hypoxanthine, bilirubin (0–60 μM) failed to prolong cell survival. In contrast, biliverdin (20–100 μM) markedly delayed hepatocyte necrosis in a concentration-dependent manner. When 0.3 mM of albumin was present, bilirubin (0–50 μM) became protective of hepatocytes, while biliverdin was less dramatically enhanced in its cytoprotective effect. In human erythrocytes exposed to peroxyl radicals, bilirubin and biliverdin inhibited 50% cell lysis at lower concentrations than Trolox and ascorbate, respectively. Albumin alone appeared less cytoprotective in red cells than in hepatocytes, but its presence enhanced the effects of both pigments on erythrocytes. Of probable physiologic relevance, bilirubin with albumin present or biliverdin alone protected hepatocytes substantially (and to a lesser extent red cells) at the normal blood levels of bilirubin (3.4–26 μM). Moreover, the fact that the pigments are cytoprotective at higher bilirubin levels (e.g., 50–100 μM) tempts the speculation that they may be circulating cytoprotectors of overlooked importance in jaundice.Key words: cytoprotection, biliverdin, bilirubin, albumin.

Darusentan is a potent inhibitor of endothelin signaling and function in both large and small arteriesThis article is one of a selection of papers published in the two-part special issue entitled 20 Years of Endothelin Research.

2010 ◽  
Vol 88 (8) ◽  
pp. 840-849 ◽  
Author(s):  
Faquan Liang ◽  
Christopher B. Glascock ◽  
Denise L. Schafer ◽  
Jennifer Sandoval ◽  
LouAnn Cable ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Potent Inhibitor ◽  
Inositol Phosphate ◽  
Contractile Activity ◽  
Binding Activity ◽  
Dependent Manner ◽  
Endothelin Receptor ◽  
Resistance Arteries ◽  
Concentration Dependent Manner

Endothelin is a potent vasoconstrictor often up-regulated in hypertension. Endothelin vasoconstriction is mediated via the G-protein coupled endothelin A (ETA) receptor present on vascular smooth muscle. Endothelin receptor antagonists (ERAs) have been shown to antagonize ET-induced vasoconstriction. We describe the primary pharmacology of darusentan, a propanoic acid based ERA currently in phase 3 clinical trials for resistant hypertension. Darusentan was tested in membrane-, cell-, and tissue-based assays to determine its biochemical and functional potency. Rat aortic vascular smooth muscle cells (RAVSMs) were characterized using flow cytometry. RAVSM membrane fractions tested in saturation experiments exhibited moderate endothelin receptor density. Receptor counting revealed that >95% of the endothelin receptors in these fractions were the ETA subtype. (S)-Darusentan competed for radiolabeled endothelin binding in RAVSM membranes with single-site kinetics, exhibiting a Ki = 13 nmol/L. (R)-Darusentan exhibited no binding activity. In cultured RAVSMs, endothelin induced increases in inositol phosphate and Ca2+ signaling, both of which were attenuated by (S)-darusentan in a concentration-dependent manner. In isolated endothelium-denuded rat aortic rings, (S)-darusentan inhibited endothelin-induced vascular contractility with a pA2 = 8.1 ± 0.14 (n = 4 animals; mean ± SD). (R)-Darusentan had no effect. The vasorelaxant potency of (S)-darusentan did not change when determined in isolated denuded rat mesenteric arterioles, suggesting a similar mode of action in both conductance and resistance arteries. In vascular smooth muscle, (S)-darusentan is an ERA with high affinity for the ET receptor, which in this preparation is predominantly ETA receptors. (S)-Darusentan inhibits endothelin-induced signaling related to pro-contractile activity and is a potent inhibitor of vasoconstriction in large and small arteries.

Urea activation of K-Cl transport in human erythrocytes

1995 ◽  
Vol 268 (4) ◽  
pp. C1018-C1025 ◽  
Author(s):  
D. M. Kaji ◽  
C. Gasson
Keyword(s):  
Time Lag ◽  
Renal Medulla ◽  
Normal Subjects ◽  
Lag Time ◽  
Human Erythrocytes ◽  
Cell Swelling ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Activated State ◽  
High Concentrations

This report prompted us to examine the effect of urea on K-Cl cotransport in human erythrocytes. In human erythrocytes, urea activated K-Cl cotransport reversibly and in a concentration-dependent manner. Pretreatment with okadaic acid abolished the urea activation of transport, suggesting that exposure to urea resulted in net dephosphorylation of the transporter or a key regulator and that the action of urea was exerted proximal to the phosphorylation-dephosphorylation step. At a concentration of 200 mM, urea activated K-Cl cotransport without any delay, even in the absence of cell swelling. However, with increasing urea concentrations, an appreciable increase in lag time was observed before the final steady-state flux was reached, suggesting that urea inhibits a regulatory kinase. The latter conclusion was also supported by the finding that, at any given urea concentration, the lag time for activation was greater than the lag time for deactivation. Mg depletion activated cotransport, and urea had no additional stimulatory effect in Mg-depleted cells. In urea-pretreated cells, swelling further activated cotransport, but without any measurable delay, in contrast to a time lag of 8 min when control cells (not exposed to urea) were swollen. The latter finding suggests that urea promotes the conversion of transporters from the resting to the partially activated state. These findings raise the possibility that high concentrations of urea in the renal medulla may play a role in the decrease in cell volume that occurs during the maturation of reticulocytes and young erythrocytes, both in normal subjects and in subjects with hemoglobinopathies.

Isolation and Characterization of Limonoids from Kigelia africana

2013 ◽  
Vol 68 (9) ◽  
pp. 1041-1048 ◽  
Author(s):  
Bushra Jabeen ◽  
Naheed Riaz
Keyword(s):  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
X Ray ◽  
X Ray Crystallography ◽  
Isolation And Characterization ◽  
Related Compounds ◽  
Absolute Stereochemistry ◽  
Cosy Nmr ◽  
C Nmr

Two new limonoids, 1-O-deacetyl-2a-methoxykhayanolide (1) and kigelianolide (2), together with deacetylkhayanolide E (3), 1-O-deacetyl-2α-hydroxykhayanolide E (4) and khayanolide B (5) were isolated from the ethyl acetate-soluble fraction of the methanolic extract of Kigelia africana. The structures of these limonoids (1-5) were elucidated by the combination of 1D (1H and 13C NMR) and 2D (HMQC, HMBC and COSY) NMR spectroscopy and mass spectrometry (EIMS, HREIMS), and in comparison with literature data of related compounds. The structure of compound 1 was further confirmed by X-ray crystallography, and the absolute stereochemistry of compounds 1 and 2 was determined by electronic circular dichroism (ECD) spectroscopy. Limonoids 1-5 showed weak inhibitory activities against the enzymes acetylcholinesterase (AChE), butyrycholinesterase (BChE) and lipoxygenase (LOX) in a concentration-dependent manner with IC50 values in the ranges 137.5 - 225.2 μM for AChE, 185.4 - 241.5 μM for BChE and 281.2 - 189.6 μM for LOX

Reduction and uptake of methylene blue by human erythrocytes

2004 ◽  
Vol 286 (6) ◽  
pp. C1390-C1398 ◽  
Author(s):  
James M. May ◽  
Zhi-chao Qu ◽  
Charles E. Cobb
Keyword(s):  
Methylene Blue ◽  
Reductase Activity ◽  
Oxidant Stress ◽  
Pentose Phosphate ◽  
Human Erythrocytes ◽  
Dependent Manner ◽  
Phenylarsine Oxide ◽  
Concentration Dependent Manner ◽  
Ferricyanide Reduction ◽  
Thiazine Dye

A thiazine dye reductase has been described in endothelial cells that reduces methylene blue (MB), allowing its uptake into cells. Because a different mechanism of MB uptake in human erythrocytes has been proposed, we measured MB uptake and reduction in this cell type. Oxidized MB (MB+) stimulated reduction of extracellular ferricyanide in a time- and concentration-dependent manner, reflecting extracellular reduction of the dye. Reduced MB was then taken up by the cells and partially oxidized to MB+. Both forms were retained against a concentration gradient, and their redox cycling induced an oxidant stress in the cells. Whereas concentrations of MB+ <5 μM selectively oxidized NAD(P)H, higher concentrations also oxidized both glutathione (GSH) and ascorbate, especially in the absence of d-glucose. MB+-stimulated ferricyanide reduction was inhibited by thiol reagents with different mechanisms of action. Phenylarsine oxide, which is selective for vicinal dithiols in proteins, inhibited MB+-dependent ferricyanide reduction more strongly than it decreased cell GSH and pentose phosphate cycle activity, and it did not affect cellular NADPH. Open erythrocyte ghost membranes facilitated saturable NAD(P)H oxidation by MB+, which was abolished by pretreating ghosts with low concentrations of trypsin and phenylarsine oxide. These results show that erythrocytes sequentially reduce and take up MB+, that both reduced and oxidized forms of the dye are concentrated in cells, and that the thiazine dye reductase activity initially responsible for MB+ reduction may correspond to MB+-dependent NAD(P)H reductase activity in erythrocyte ghosts.

scholarly journals Synergistic effects of C-peptide and insulin on low O2-induced ATP release from human erythrocytes

2013 ◽  
Vol 305 (11) ◽  
pp. R1331-R1336 ◽  
Author(s):  
Jennifer P. Richards ◽  
Alan H. Stephenson ◽  
Mary L. Ellsworth ◽  
Randy S. Sprague
Keyword(s):  
Skeletal Muscle ◽  
Synergistic Effects ◽  
Atp Release ◽  
Peripheral Circulation ◽  
Human Erythrocytes ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
C Peptide ◽  
Physiological Importance

Erythrocytes participate in the matching of oxygen (O2) delivery with local need in skeletal muscle via the release of O2and the vasodilator, ATP. It was reported that a concentration of insulin found in humans with insulin resistance inhibits low O2-induced ATP release. However, in vivo, insulin is coreleased with connecting peptide (C-peptide) at equimolar concentrations, but because of the shorter insulin half-life, the peptides circulate at ratios of C-peptide to insulin ranging from 1:1 to 6:1. Here, we investigate the hypothesis that C-peptide and insulin work synergistically to maintain low O2-induced ATP release from human erythrocytes. Using a thin-film tonometer to alter O2tension, we determined that either C-peptide or insulin alone inhibits low O2-induced ATP release in a concentration-dependent manner; however, coadministration of the peptides at a 1:1 ratio does not ( n = 5; P < 0.05). Because this ratio of C-peptide to insulin is not present in vivo for extended periods, we also investigated the effect of additional physiological ratios on ATP release. In the presence of insulin concentrations that would be found in fasting humans (0.05 nM), C-peptide to insulin ratios of 4:1 and 6:1 did not adversely affect low O2-induced ATP release. However, at a concentration of insulin found in the peripheral circulation of humans under postprandial conditions (0.5 nM), a ratio of C-peptide to insulin of 6:1 inhibited low O2-induced ATP release ( n = 5). These findings demonstrate a heretofore unrecognized synergism between C-peptide and insulin that could have physiological importance in the regulation of perfusion distribution in skeletal muscle.

scholarly journals Superoxide generation is inhibited by phospholipase A2 inhibitors. Role for phospholipase A2 in the activation of the NADPH oxidase

1989 ◽  
Vol 264 (1) ◽  
pp. 249-255 ◽  
Author(s):  
L M Henderson ◽  
J B Chappell ◽  
O T G Jones
Keyword(s):  
Arachidonic Acid ◽  
Nadph Oxidase ◽  
Phospholipase A2 ◽  
Potent Inhibitor ◽  
Dependent Manner ◽  
Superoxide Generation ◽  
Concentration Dependent Manner ◽  
Ic50 Value ◽  
Phospholipase A2 Inhibitors ◽  
Stimulation Of

The stimulation of O2.- generation by phorbol 12-myristate 13-acetate (PMA) in human neutrophil-derived cytoplasts was inhibited by a variety of phospholipase A2 inhibitors in a concentration-dependent manner. Inhibition was found to be independent of the order of addition of the inhibitor and PMA. The most potent inhibitor, RO 31-4639, inhibited O2.- generation with an IC50 value (concentration causing 50% inhibition) of 1.5 microM. The addition of either arachidonic acid or SDS, in the presence of the inhibitors, was able to restore O2.- generation. The results suggest that arachidonic acid, released by phospholipase A2, is necessary for both the activation and the maintenance of O2.- generation by the NADPH oxidase.

Nucleoside Transport. I. A Mediated Process in Human Erythrocytes

1971 ◽  
Vol 49 (2) ◽  
pp. 262-270 ◽  
Author(s):  
J. M. Oliver ◽  
A. R. P. Paterson
Keyword(s):  
Competitive Inhibition ◽  
Diffusion Mechanism ◽  
Human Erythrocytes ◽  
Nucleoside Transport ◽  
Facilitated Diffusion ◽  
Uridine Uptake ◽  
Saturation Kinetics ◽  
Pyrimidine Bases ◽  
Thymidine Transport ◽  
Broad Specificity

The transport of nucleosides by human erythrocytes has been studied by measuring disappearance of 14C-labelled uridine and thymidine from incubation media; saturation kinetics and competitive inhibition of uridine uptake by formycin B were observed. Uridine and thymidine transport were nonconcentrative under incubation conditions in which cellular ATP concentrations were maintained. Efflux of uridine or thymidine from preloaded cells was induced by an inward flow of various nucleosides, but not by purine or pyrimidine bases. It is concluded that the transport of nucleosides across the plasma membrane of human erythrocytes is accomplished by a nonconcentrative, 'facilitated diffusion' mechanism of broad specificity.

The Anti-Atherogenic Properties of Sesamin are Mediated via Improved Macrophage Cholesterol Efflux Through PPARγ1-LXRα and MAPK Signaling

2014 ◽  
Vol 84 (1-2) ◽  
pp. 79-91 ◽  
Author(s):  
Amin F. Majdalawieh ◽  
Hyo-Sung Ro
Keyword(s):  
Cholesterol Efflux ◽  
Transcriptional Activity ◽  
Molecular Mechanisms ◽  
Foam Cell ◽  
Mapk Signaling ◽  
Luciferase Reporter ◽  
Foam Cell Formation ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Macrophage Cholesterol Efflux

Background: Foam cell formation resulting from disrupted macrophage cholesterol efflux, which is triggered by PPARγ1 and LXRα, is a hallmark of atherosclerosis. Sesamin and sesame oil exert anti-atherogenic effects in vivo. However, the exact molecular mechanisms underlying such effects are not fully understood. Aim: This study examines the potential effects of sesamin (0, 25, 50, 75, 100 μM) on PPARγ1 and LXRα expression and transcriptional activity as well as macrophage cholesterol efflux. Methods: PPARγ1 and LXRα expression and transcriptional activity are assessed by luciferase reporter assays. Macrophage cholesterol efflux is evaluated by ApoAI-specific cholesterol efflux assays. Results: The 50 μM, 75 μM, and 100 μM concentrations of sesamin up-regulated the expression of PPARγ1 (p< 0.001, p < 0.001, p < 0.001, respectively) and LXRα (p = 0.002, p < 0.001, p < 0.001, respectively) in a concentration-dependent manner. Moreover, 75 μM and 100 μM concentrations of sesamin led to 5.2-fold (p < 0.001) and 6.0-fold (p<0.001) increases in PPAR transcriptional activity and 3.9-fold (p< 0.001) and 4.2-fold (p < 0.001) increases in LXR transcriptional activity, respectively, in a concentration- and time-dependent manner via MAPK signaling. Consistently, 50 μM, 75 μM, and 100 μM concentrations of sesamin improved macrophage cholesterol efflux by 2.7-fold (p < 0.001), 4.2-fold (p < 0.001), and 4.2-fold (p < 0.001), respectively, via MAPK signaling. Conclusion: Our findings shed light on the molecular mechanism(s) underlying sesamin’s anti-atherogenic effects, which seem to be due, at least in part, to its ability to up-regulate PPARγ1 and LXRα expression and transcriptional activity, improving macrophage cholesterol efflux. We anticipate that sesamin may be used as a therapeutic agent for treating atherosclerosis.

Sign in / Sign up

Export Citation Format

Share Document