Deoxyglucose and 3-O-methylglucose transport in untreated and ATP-depleted Novikoff rat hepatoma cells. Analysis by a rapid kinetic technique, relationship to phosphorylation and effects of inhibitors

Antioxidant and Inhibitory Effects of Saponin Extracts from Dianthus basuticus Burtt Davy on Key Enzymes Implicated in Type 2 Diabetes In vitro

Context:

Dianthus basuticus is a plant of South African origin with various acclaimed pharmaceutical potentials.

Aims:

This study explored the antioxidant and antidiabetic activities of saponin extract from D. basuticus in vitro.

Materials and Methods:

Antioxidant activity of saponin was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and nitric oxide (*NO)-free radical scavenging activity while antidiabetic potentials were measured by the α-amylase and α-glucosidase inhibitory activities of the saponin extract.

Results:

The results showed that the saponin extract, compared with quercetin, displayed better DPPH (IC₅₀ = 6.95 mg/ml) and NO (IC₅₀ = 3.31 mg/ml) radical scavenging capabilities. Similarly, the saponin extracts elicited stronger α-glucosidase (IC₅₀ = 3.80 mg/ml) and moderate α-amylase (IC₅₀ = 4.18 mg/ml) inhibitory activities as compared to acarbose. Saponin exhibited a competitive mode of inhibition on α-amylase with same maximum velocity (Vmax) of 0.0093 mM/min for saponin compared with control 0.0095 mM/min and different the Michaelis constant (Km) values of 2.6 × 10^-6 mM and 2.1 × 10^-5 mM, respectively, while for α-glucosidase, the inhibition was uncompetitive, Vmax of 0.027 mM/min compared with control 0.039 mM/min and Km values of 1.02 × 10^-6 mM and 1.38 × 10^-6 mM, respectively. The gas chromatography-mass spectrometric analysis revealed the presence of bioactive like β- and α-amyrin, 3-O-methyl-D-glucose, methyl commate, and olean-12-en-3-beta-ol.

Conclusion:

Overall, the data suggested that the saponin extract from D. basuticus has potentials as natural antioxidants and antidiabetics.

SUMMARY

Saponin extract from Dianthus basuticus displayed promising antidiabetic and antioxidant activity

Saponin competitively and uncompetitively inhibited a-amylase and a-glucosidase, respectively

The stronger inhibition of α-glucosidase and moderate inhibition of α-amylase by saponin extract from D. basuticus is promising good antidiabetes compared with existing drugs with associated side effects.

Abbreviations used: DPPH: 2,2-diphenyl-1-picrylhydrazyl, Km: The Michaelis constant, Vmax: Maximum velocity, ROS: Reactive oxygen species, NIDDM: Non-insulin-dependent diabetes mellitus, UFS: University of the Free State, GC-MS: Gas chromatography-mass spectrometric, MS: Mass spectrometry, NIST: National Institute of Standards and Technology, DNS: 3,5-dinitrosalicylic acid, NO: Nitric oxide, RNS: Reactive nitrogen species, PNPG: p-Nitrophenyl-α-D-glucopyranoside.

Resolution of the direct interaction with and inhibition of the human GLUT1 hexose transporter by resveratrol from its effect on glucose accumulation

Resveratrol acts as a chemopreventive agent for cancer and as a potential antiobesity and antidiabetic compound, by leading to reduced body fat and improved glucose homeostasis. The exact mechanisms involved in improving hyperglycemic state are not known, but most of the glucose uptake into mammalian cells is facilitated by the GLUT hexose transporters. Resveratrol is structurally similar to isoflavones such as genistein, which inhibit the glucose uptake facilitated by the GLUT1 hexose transporter. Here we examined the direct effects of resveratrol on glucose uptake and accumulation in HL-60 and U-937 leukemic cell lines, which express mainly GLUT1, under conditions that discriminate transport from the intracellular substrate phosphorylation/accumulation. Resveratrol blocks GLUT1-mediated hexose uptake and thereby affects substrate accumulation on these cells. Consequently, we characterized the mechanism involved in inhibition of glucose uptake in human red cells. Resveratrol inhibits glucose exit in human red cells, and the displacement of previously bound cytochalasin B revealed the direct interaction of resveratrol with GLUT1. Resveratrol behaves as a competitive blocker of glucose uptake under zero-trans exit and exchange kinetic assays, but it becomes a mixed noncompetitive blocker when zero-trans entry transport was assayed, suggesting that the binding site for resveratrol lies on the endofacial face of the transporter. We propose that resveratrol interacts directly with the human GLUT1 hexose transporter by binding to an endofacial site and that this interaction inhibits the transport of hexoses across the plasma membrane. This inhibition is distinct from the effect of resveratrol on the intracellular phosphorylation/accumulation of glucose.

Preservation of mouse sperm by convective drying and storing in 3-O-methyl-D-glucose

With the fast advancement in the genetics and bio-medical fields, the vast number of valuable transgenic and rare genetic mouse models need to be preserved. Preservation of mouse sperm by convective drying and subsequent storing at above freezing temperatures could dramatically reduce the cost and facilitate shipping. Mouse sperm were convectively dried under nitrogen gas in the Na-EGTA solution containing 100 mmol/L 3-O-methyl-D-glucose and stored in LiCl sorption jars (Relative Humidity, RH, 12%) at 4°C and 22°C for up to one year. The functionality of these sperm samples after storage was tested by intracytoplasmic injection into mouse oocytes. The percentages of blastocysts produced from sperm stored at 4°C for 1, 2, 3, 6, and 12 months were 62.6%, 53.4%, 39.6%, 33.3%, and 30.4%, respectively, while those stored at 22°C for 1, 2, and 3 months were 28.8%, 26.6%, and 12.2%, respectively. Transfer of 38 two- to four-cell embryos from sperm stored at 4°C for 1 year produced two live pups while 59 two- to four-cell embryos from sperm stored at 22°C for 3 months also produced two live pups. Although all the pups looked healthy at 3 weeks of age, normality of offspring produced using convectively dried sperm needs further investigation. The percentages of blastocyst from sperm stored in the higher relative humidity conditions of NaBr and MgCl(2) jars and driest condition of P(2)O(5) jars at 4°C and 22°C were all lower. A simple method of mouse sperm preservation is demonstrated. Three-O-methyl-D-glucose, a metabolically inactive derivative of glucose, offers significant protection for dried mouse sperm at above freezing temperatures without the need for poration of cell membrane.

Hypoxia but not inflammation augments glucose uptake in human macrophages: Implications for imaging atherosclerosis with 18fluorine-labeled 2-deoxy-D-glucose positron emission tomography

OBJECTIVES

This study investigated the regulation of glucose uptake in cells that participate in atherogenesis by stimuli relevant to this process, to gain mechanistic insight into the origin of the (18)fluorine-labeled 2-deoxy-D-glucose (FdG) uptake signals observed clinically.

BACKGROUND

Patient studies suggest that positron emission tomography (PET) using FdG can detect "active" atherosclerotic plaques, yet the mechanism giving rise to FdG signals remains unknown.

METHODS

We exposed cells to conditions thought to operate in atheroma and determined rates of glucose uptake.

RESULTS

Hypoxia, but not pro-inflammatory cytokines, potently stimulated glucose uptake in human macrophages and foam cells. Statins attenuated this process in vitro, suggesting that these agents have a direct effect on human macrophages. Immunohistochemical study of human plaques revealed abundant expression of proteins regulating glucose utilization, predominantly in macrophage-rich regions of the plaques-regions previously proved hypoxic. Smooth-muscle cells and endothelial cells markedly increased rates of glucose uptake when exposed to pro-inflammatory cytokines.

CONCLUSIONS

Glucose uptake and, probably, FdG uptake signals in atheroma may reflect hypoxia-stimulated macrophages rather than mere inflammatory burden. Cytokine-activated smooth-muscle cells also may contribute to the FdG signal.

Acute regulation of glucose transport in a monocyte-macrophage cell line: Glut-3 affinity for glucose is enhanced during the respiratory burst

Activation of the respiratory burst imposes acute metabolic demands on phagocytic cells. These are met by mobilizing internal energy stores and by increasing the utilization of exogenous energy, including glucose in the circulation. To determine whether the increased glucose uptake that is known to be associated with the respiratory burst involves the regulation of glucose transporter molecules, the intrinsic transport properties of glucose transporters on the macrophage cell line RAW 264.7 were determined after activation with PMA, N-formyl-methionine-leucine-phenylalanine (fMLP) and the cytokines granulocyte/macrophage colony-stimulating factor (GM-CSF) and interleukin 3 (IL-3). Treatment with PMA resulted in a 2-fold increase in respiratory burst activity within 10 min; this was associated with a 30-50% increase in 2-deoxyglucose uptake and a 4-fold increase in transporter affinity for glucose. Similarly, fMLP, GM-CSF and IL-3 treatments stimulated 2-deoxyglucose uptake that was associated with a 3-4-fold increase in transporter affinity for glucose. To determine whether the changes observed in 2-deoxyglucose uptake in response to PMA, fMLP and growth factors were influenced by phosphorylation of the sugar, 3-O-methylglucose, which is not phosphorylated, was used. Increased 3-O-methylglucose uptake and increased transporter affinity for glucose were also observed after PMA, fMLP and GM-CSF treatments. Whereas both fMLP and GM-CSF stimulated superoxide production, IL-3 failed to activate respiratory burst activity. The protein kinase inhibitors genistein and staurosporine inhibited the increase in 2-deoxyglucose uptake observed with fMLP and GM-CSF, and partly reversed the affinity increase towards that of untreated control cells. In contrast, the phosphatidylinositol 3-kinase inhibitor wortmannin had little effect on 2-deoxyglucose uptake in response to these activators. Western blotting with subtype-specific antisera showed that Glut-3 was the predominant transporter on RAW 264.7 cells. These studies demonstrate that acute regulation of glucose transporters occurs in response to activators that promote respiratory burst activity, and show that this regulation involves both tyrosine kinases and protein kinase C activity.

Experimental models, protocols, and reference values for evaluation of iodinated analogues of glucose

For an iodinated analogue of glucose to be useful for evaluating glucose uptake using single-photon emission computed tomography (SPECT), it must enter the cell via the same transporter as glucose and accumulate within the cell without being degraded. The biological behavior of the iodinated tracer must therefore be similar to that of 2-deoxy-D(-)[1-14C]-glucose (2-DG). In the present study, four experimental models (biodistribution in mouse, isolated rat heart, human erythrocytes in suspension and cultured neonatal rat cardiomyocytes) have been chosen and protocols have been set up which allow for the examination of small quantities of iodinated analogues of glucose. The uptakes of 2-DG and of L(-)[1-14C]-glucose have been measured in these models to establish reference values which will be compared with uptake values for iodinated analogues of glucose.

Regulation of glucose transport by pioglitazone in cultured muscle cells

Recent evidence suggests that pioglitazone, a thiazolidinedione hypoglycemic agent, acts by increasing insulin responsiveness at the peripheral level. We studied the effect of pioglitazone (1 to 50 micrograms/mL) on the glucose transporter and glucose transport in BC3H-1 cells, a continuously cultured skeletal muscle cell line lacking the myoD transcription factor required for cell fusion. Glucose-fed cells (25 mmol/L) responded to insulin with a more than twofold increase in 2-deoxyglucose (2-DOG) uptake as compared with baseline. Treating these cells with pioglitazone alone for 24 hours resulted in a dose-dependent increase in hexose uptake, reaching twofold at 50 micrograms/mL. Combining long-term pioglitazone (10 micrograms/mL for 24 hours) and short-term insulin treatment resulted in an additive effect on 2-DOG uptake over a wide range of insulin concentrations (0.1 to 100 nmol/L) without the desensitization to 2-DOG uptake seen in other systems following long-term insulin administration. To determine the basis of the increased glucose uptake response, the level of specific mRNA and immunoreactive glucose transporter protein was determined. Northern and Western blot studies on glucose-treated cells (25 mmol/L) showed that glucose transporter mRNA and protein increased in parallel following treatment with either pioglitazone or insulin alone. The combination of insulin with pioglitazone resulted in an additive stimulation of glucose transporter mRNA and protein. In summary, pioglitazone stimulates hexose uptake both independently and in combination with insulin in BC3H-1 myocytes. These effects are largely accounted for by increases in glucose transporter mRNA and protein, indicating its potential efficacy in the treatment of non-insulin-dependent diabetes mellitus (NIDDM).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the GLUT1 glucose transporter in cultured myocytes: total number and subcellular distribution as determined by photoaffinity labelling

We have used the impermeant photoaffinity label 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-[2-3H] 1,3-bis-(D-mannos-4-yloxy)-2-propylamine (ATB-[2-3H]BMPA) to identify and quantify the glucose transporters on the surface of BC3H-1 cells, a continuously cultured skeletal-muscle cell line lacking the MyoD transcription factor required for cell fusion. ATB-[2-3H]BMPA was used in combination with immunoprecipitation of the GLUT1 glucose transporter, the only isoform expressed in these cells. The total cellular GLUT1 content was also determined by photolabelling and immunoprecipitation after cell permeabilization with digitonin (0.025%). In glucose-starved cells, 85% of the glucose transporters were present at the cell surface in the basal state, with little change in response to insulin (200 nM), correlating with lack of additional 2-deoxyglucose uptake in response to insulin. Feeding the cells with glucose (25 mM) for 24 h resulted in an 80% decrease in the total GLUT1 content relative to starved cells, of which only 25% were present on the cell surface. This was associated with an 85% decrease in 2-deoxyglucose uptake. In addition, acute stimulation of the fed cells with insulin or phorbol 12-myristate 13-acetate (PMA) led to an increase in GLUT1 at the cell surface, and, in correspondence, an increase in 2-deoxyglucose uptake by approx. 2- and 4-fold respectively. We conclude that exofacial photoaffinity labelling of glucose transporters with ATB-[2-3H]BMPA in the presence and absence of digitonin, followed by specific immunoprecipitation, provides an accurate measure of total and cell-surface glucose transporters in differentiated BC3H-1 muscle cells. This technique demonstrates that glucose pre-feeding (1) decreases the total number of GLUT1 and (2) redistributes the majority of the remaining transporters to an intracellular site, where they can now be translocated to the cell surface in response to insulin and PMA.

Selection of a lysine-resistant CHO-K1 mutant with reduced amino acid transport through multiple systems

High levels of L-lysine were used to select for resistant variants of Chinese hamster ovary (CHO-K1) cells. Surviving colonies were screened for altered lysine transport and two with reduced uptake were picked. Clone CH-Kr, derived from the more severely affected colony, was analyzed in detail. In starved cells the Vmax of lysine uptake in CH-Kr was half that of CHO while Km was unaltered. The intracellular pool of lysine, a substrate of cationic amino acid transport system y+, was significantly lower in CH-Kr. However, transport and pools of other amino acids, which are not substrates of y+, were also reduced in CH-Kr, as was the internal sodium concentration, while hexose import was increased. It appears that the mutation in CH-Kr is pleiotropic, affecting some general aspects of amino acid transport.

Evidence that activation of 2-deoxy-D-glucose transport in rat thymocyte suspensions results from enhanced coupling between transport and hexokinase activity

1. Suspensions of rat thymocytes accumulate free 2-deoxy-D-glucose (2-dGlc) within the cytosol to a concentration approx. 25-fold above the external concentration. This active accumulation was enhanced by 40 nM-phorbol 12-myristate 13-acetate (phorbol). 2. The Km for zero-trans uptake in control cells was 2.3 +/- 0.14 mM and Vmax. was 0.41 +/- 0.08 mumol/min per 10(10) cells (n = 6). In cells treated with phorbol (40 nM) the Km for zero-trans uptake was 1.2 +/- 0.13 mM and Vmax. 0.46 +/- 0.03 mumol/min per 10(10) cells (n = 6). The Km was decreased significantly by phorbol (P less than 0.01). 3. Phorbol-dependent activation of thymocytes delayed exit of free 2-dGlc into sugar-free solution and prevented exchange exit. Activation had no effect on 3-O-methyl D-glucoside (3-OMG) exit. 4. Coupling of 2-dGlc transport to hexokinase activity was determined by observing the effects of various concentrations of unlabelled cytosolic 2-dGlc on influx of labelled 2-dGlc into the hexose phosphate pool. In control cells this coupling was 0.81 +/- 0.02 and in phorbol-activated cells it was 0.92 +/- 0.01 (P less than 0.01). 5. The high-affinity inhibitor of hexokinase, mannoheptulose, inhibited uptake of 2-dGlc in both control and phorbol-treated cells. These data are consistent with a model for activation of sugar transport in which hexokinase activity is integrated with the sugar transporter at the endofacial surface. The results suggest that phorbol increases the degree of coupling transport with hexokinase activity, thereby leading to an increase in the rate of uptake of 2-dGlc, a decrease in exit of free 2-dGlc from the cytosol and an increase in free 2-dGlc accumulation.

Characterization of the glucose transporter from rat brain synaptosomes

Our goal was to characterize the glucose transporter in synaptosomes and to compare it to the different forms of transporter already identified. Cross-reactivity with antibodies to the human erythrocyte transporter, Km of glucose uptake, reversibility of NEM inhibition of transport, and insulin sensitivity were all examined. Immunoblotting showed a band at Mr 40,000, and the Km of glucose uptake was determined to be about 4 mM. Treatment with NEM caused irreversible inhibition of glucose uptake, while incubation with insulin failed to stimulate uptake. The results suggest that the transporter in synaptosomes resembles the human erythrocyte transporter.

Comparative metabolic effects of fructose and glucose in human fibroblast cultures

The comparative metabolic effects of fructose and glucose were determined in human fibroblast cultures. Cells were grown in four different media containing 5.5 and 27.5 mM of glucose and fructose, respectively. For these two hexoses, we compared their uptake, consumption, and conversion into 14CO2 and 14C-lipids. D-Fructose was taken up in fibroblasts by an unsaturable process and its consumption was much smaller than that of D-glucose. Whatever the experimental procedure, the glycogen content of cells grown in fructose media was significantly lower than of those grown in glucose media. Labeling of fructose and glucose with 14C showed that more carbon from fructose than from glucose was incorporated into CO2 and glycerolipids. The relative distribution of 14C in the different lipid fractions was similar for both hexoses. These results indicated that the pathways of intermediary metabolism in fibroblast cultures were influenced by the nature of the carbohydrate present in the culture medium and that fructose was a better lipogenic substrate than glucose in human fibroblast cultures.

Effect of endotoxin-induced monokines on glucose metabolism in the muscle cell line L6

Exposure of fully differentiated L6 myotubes to a crude monokine preparation from endotoxin-stimulated RAW 264.7 cells resulted in a rapid and substantial (70%) increase in fructose 2,6-bisphosphate concentration coincident with a depletion of cellular glycogen and an increased lactate production. During the time required for glycogen depletion (3 hr), stimulation of 3-O-methyl-D-glucose and 2-deoxy-D-glucose uptake was initiated and observed to reach a maximum enhancement of 200% 12-15 hr later. The monokine had no effect on the Km value for 2-deoxy-D-glucose uptake (1.1 mM), while Vmax was increased from 912 to 2400 pmol/min per mg of protein. The increase was cytochalasin B inhibitable and was dependent on protein synthesis. Photoaffinity labeling and equilibrium binding studies with [3H]cytochalasin B support the hypothesis that this increase in hexose transport was due to an increase in hexose transporters present in the plasma membrane. Purified recombinant interleukin-1 alpha had no effect on hexose transport, whereas purified recombinant cachetin/tumor necrosis factor did stimulate hexose uptake, with half-maximal stimulation occurring at 36 nM. Although cachetin accounts for most of the biological activity associated with the crude monokine preparations, it is not the only monokine capable of inducing glucose transport in L6 cells. Specific immunoabsorption of cachectin/tumor necrosis factor from the crude monokine preparation revealed a monokine that had a similar bioactivity at extremely low concentrations on L6 cells.

Modulation of the hypoxic toxicity and binding of misonidazole by glucose

The hypoxic toxicity and binding of misonidazole (MISO) requires metabolic reduction. The influence of glucose on the toxicity and binding of MISO was studied because glucose is a major substrate for the supply of NADPH through the hexose monophosphate pathway (HMP). Hypoxic EMT6/Ro cells (10(6) cells ml-1) were incubated with varying concentrations of glucose (0.015 mM to 5 mM). The initial rate of glucose transport was found to increase linearly with the extracellular glucose concentration up to 5 mM (0.038 nmol glucose 10(-6) cells sec-1). About 1.5 percent of the total glucose consumed went through the HMP for hypoxic cells in 5 mM glucose. The rate of HMP progressively decreased as the glucose concentration was lowered. When exposed to 5 mM MISO, the HMP was stimulated. This stimulation declined from 3.2 times in 5 mM glucose to barely detectable below 1 mM glucose. Both the hypoxic toxicity and binding of 5 mM MISO to the acid-insoluble fraction were decreased as the concentration of glucose was lowered. Below 0.5 mM glucose, no significant toxicity due to MISO was observed. There was an initial burden of 2.5 nmol MISO 10(-6) cells bound with little toxicity. After this initial burden, the terminal slope was 1.8 mol MISO bound 10(-6) cells (63 percent decrease in the surviving fraction). These results indicate that glucose concentrations lower than 5 mM can decrease the HMP rate and the toxicity and binding of MISO to hypoxic cells, and imply that calibration curves with normal and low glucose concentrations should be used to estimate the possible hypoxic fraction when MISO is used as a hypoxic probe in vivo.

Hexose transport in L6 rat myoblasts. I. Rate-limiting step, kinetic properties, and evidence for two systems

The hexose transport system of undifferentiated L6 rat myoblasts was investigated. 2-Deoxy-D-glucose (2-DOG) and 2-deoxy-2-fluoro-D-glucose (2FG) were used as analogues to investigate the rate-limiting step of hexose uptake into the cell. Virtually all of the 2-DOG or 2FG taken up into the cell was found to be in the phosphorylated form. No significant pool of intracellular free sugar could be detected. This demonstrates that hexose transport, not phosphorylation, is the rate-limiting step. The inhibitory effect of various glucose analogues on 2-DOG and 3-O-methyl-D-glucose (3-OMG) uptake revealed that these two sugars may be taken up into the cell by different carriers. In addition, kinetics analysis of the transport of both sugars also indicates that two hexose transport systems may be present in L6 cells. 2-DOG is transported by high and low affinity transport systems (Km 0.6 mM and 2.9 mM, respectively), whereas 3-OMG is transported by a low affinity system (Km 3.5 mM). Treatment of cells with ionophores or energy uncouplers results in inactivation of the high affinity system, but not the low affinity system.

Scintigraphy with [18F]2-fluoro-2-deoxy-D-glucose of cancer patients

Computerized dynamic gamma camera scintigraphy was performed with [18F]2-fluoro-2-deoxy-D-glucose [( 18F]FDG) on 10 patients with different cancers; tumor perfusion was evaluated in four patients with 99mTc-DPD. All tumors were visible in the [18F]FDG scans with tumor-to-tissue image contrast ratios of 1.2-11.7. Tumor perfusion exceeded that of the surrounding normal tissue in three of the four patients studied. Tumor-to-normal tissue [18F]FDG ratios were plotted as a function of the time. Two types of curves emerged: curves showing a linear increase in the ratio and curves showing a constant value for the ratio. These studies show that [18F]FDG can be used for clinical tumor imaging with a gamma camera, and that there appears to be biological differences in tumor uptake of [18F]FDG.

Impairment of induction of delta-aminolevulinic acid synthase by gluconeogenic amino acids and carbohydrates in vitro

This study was undertaken in a system of chick embryo liver cells incubated in Earle's Basal Salt Solution with hormones. Impairment of induction of delta-aminolevulinic acid synthase (ALAS) by allyl-isopropylacetamide (AIA) was observed in the presence of glucose. Fructose and various gluconeogenic substances including gluconeogenic amino acids had a similar effect. Leucine, which is purely ketogenic, did not influence induction of ALAS. SH-containing amino acids increased induction of ALAS by AIA. The glucose analogues 3-O-methylglucose and 2-deoxyglucose did not impair induction of ALAS by AIA. The inhibitory effect of glycerol, fructose, and glycine was not affected by 3-O-methylglucose but was reversed by 2-deoxyglucose. The results indicate that the salutary effects of proteins on acute attacks of hepatic porphyria are probably caused by their gluconeogenic properties and that glucose-6-phosphate, or metabolite of glucose-6-phosphate that is not in the glycolytic pathway, is the active agent that leads to the glucose-like effect.

A kinetic analysis of hexose transport in cultured human lymphocytes (IM-9)

3-O-Methyl-D-glucose transport across the plasma membrane of cultured human lymphocytes of the IM-9 line was followed for net entry into sugar-free cells (zero trans entry), net exit into sugar-free medium (zero trans exit) and for equilibration of labelled sugar in cells with the same sugar concentration in the intracellular water as in the medium (equilibrium exchange). The measurements were performed at 37 degrees C (pH 7.4). Equilibrium exchange of 1 mM 3-O-methylglucose (t 1/2 about 7 S) was exponential, suggesting a homogeneous cell suspension. Initial rates of transport showed a Michaelis-Menten dependency on the sugar concentration. The transport system was found to be asymmetric with the following kinetic parameters. Zero trans entry: Km = 2.8 mM, Vmax = 10.7 mM X min-1. Zero trans exit: Km = 9.5 mM, Vmax = 37.9 mM X min-1. Equilibrium exchange: Km = 9.9 mM, Vmax = 44.0 mM X min-1. Finally, the affinity constant for the internal site was measured as approx. 1.2 mM using the infinite cis protocol.

Two mechanisms of adriamycin-DNA interaction in L1210 cells

Among the effects exerted by adriamycin (ADR), interaction with DNA is closely related to cytotoxicity. The interaction results in the formation of protein-associated DNA single-strand breaks (PA-SSB) and, at drug levels greater than or equal to 2.8 X 10(-6) M, also in "direct" (nonenzymatic) DNA single-strand breaks (D-SSB). To characterize the two types of DNA lesions, euoxic mouse leukemia L1210 cells were treated with various antioxidant agents in the presence of 2.8 X 10(-6), X 10(-5), or X 10(-4) M concentrations of ADR. The enzymes superoxide dismutase (200 micrograms/ml) or catalase (250 micrograms/ml), the OH' scavengers dimethyl sulfoxide (70 mM) or ethanol (70 mM), and an inhibitor of superoxide production, 2-deoxy-glucose (1 and 10 mM), reduced the frequency of D-SSB to 18.3 to 68.2% of its level in ADR-treated controls, while the frequency of PA-SSB remained unchanged. These observations seem to indicate that ADR-mediated free radicals cause discernible DNA damage in euoxic cells only at very high drug concentrations, greater than the peak plasma level achievable clinically following i.v. bolus. At lower ADR levels, relevant to clinical use, another type of interaction between the drug and DNA prevails, which apparently does not involve a free-radical mechanism.

Purines as 'hyper-repressors' of glucose transport. A role for phosphoribosyl diphosphate

Under selected conditions the rate of glucose transport and the intracellular phosphoribosyl diphosphate (PPRibP) concentrations of chick-embryo fibroblasts are inversely correlated. This relationship holds when cells are incubated with mannose, fructose, xylose or various concentrations of glucose. The metabolic inhibitors 2,4-dinitrophenol, rotenone and Methylene Blue increased glucose transport and decreased PPRibP. The addition of any pyrimidine or purine base or ribonucleoside dramatically depleted PPRibP pools, regardless of the carbon source. Addition of guanine (10 microM) or hypoxanthine (100 microM) decreased transport in glucose-grown chick cells to barely detectable values, but did not affect increases observed in cells depressed by substitution of xylose for glucose. Guanosine, inosine and the purine analogues 6-thioguanine, 6-thioguanosine, 8-azaguanine and 6-methylmercaptopurine riboside sharply decreased transport in glucose-grown cells and blocked the increase in transport resulting from the replacement of glucose by fructose or xylose in the culture medium.

Counter-transport in chick embryo fibroblasts. A significant factor in measurement of glucose entry

Enhanced rates of carrier-mediated 3-O-methyl-D-glucose (0.1 mM) transport were observed in primary cell cultures of chicken embryo fibroblasts deprived of glucose for 1 day. The addition of 5.5 mM-glucose, glucosamine or 2-deoxy-D-glucose for 15 min (37 degrees C) to glucose-starved cultures followed by washing and immediate measurement of 3-O-methyl-D-glucose transport resulted in an apparent further stimulation of transport. Transport stimulation increased with increasing concentrations of the added preincubation sugar and was observed at test concentrations ranging from 0.1 mM- to 10 mM-3-O-methyl-D-glucose. This enhancement occurred when the preloaded sugar was rapidly effluxing from cells and was eliminated by allowing cultures to incubate in buffer without sugar for 30 min (37 degrees C) after the removal of hexose and before measuring transport. A transient overshoot in the cumulative uptake of 3-O-methyl-D-glucose was observed in glucose-starved cultures that were pre-incubated in the presence of 55 mM-glucose or -glucosamine for 15 min (37 degrees C). These data suggest that counter-transport accounts for the apparent enhancement of glucose-transport capability observed in glucose-starved cells when they are briefly re-exposed to hexose.

Effect of glucose uptake on growth rate of mouse 3T3 cells

The objective of this investigation was to determine whether the rate of glucose uptake by mouse 3T3 cells was a primary determinant of growth rate. The experimental approach was to control the rate of glucose uptake into intracellular pools by supplying this sugar at varying concentration in minimal Eagle's medium with dialyzed serum in the absence and presence of 6-deoxy-D-glucose, a metabolically inert homomorphic analog of D-glucose that competitively inhibits the uptake of D-glucose. Total hexose (D-glucose and 6-deoxy-D-glucose) concentration was maintained at the physiological concentration of 5.5 mM, in order to maintain saturation and maximum activity of the D-glucose transport system; thus the flux of D-glucose into the cell was controlled by adjusting its concentration relative to its competing nonmetabolizable analog. It was found that even when the concentration of D-glucose was reduced to 0.7 mM, one eighth of the "normal" level of 5.5 mM, and 6-deoxy-D-glucose was present in sevenfold excess (4.8 mM), conditions under which glucose uptake was reduced to 20% of that shown by cells in the presence of 5.5 mM D-glucose, and intracellular pools of glucose and phosphorylated sugars derived from glucose were reduced to approximately 14% of normal, there was not a significant decrease in growth rate. These data support the view that the rate of glucose uptake is not a primary determinant of growth rate under the usual conditions of cell culture.

6-deoxy-D-glucose and D-xylose: analogs for the study of D-glucose transport by mouse 3T3 cells

6-Deoxy-D-glucose and D-xylose, structural homomorphs of D-glucose that lack a 6-hydroxyl group or a 6-hydroxymethyl group, respectively, are transported efficiently by mouse 3T3 cells, with good affinity and high specificity for the D-glucose transport system. Since these analogs lack the 6-hydroxyl group, which is the site of phosphorylation of glucose by hexokinase, they are taken up and are recoverable from cells in an unchanged state. Thus, 6-deoxy-D-glucose and D-xylose offer advantages as transport substrates over 2-deoxy-D-glucose, which is phosphorylated by intercellular hexokinases, and 3-O-methyl-D-glucose, which shows a lower specificity for the D-glucose transport system.

Antiplatelet therapy reduces aortic intimal hyperplasia distal to small diameter vascular prostheses (PTFE) in nonhuman primates

While the use of prosthetic grafts in small diameter arterial reconstruction is required when suitable autogenous graft material is unavailable, late occlusion of prosthetic grafts caused by proliferative lesions has been described. This study evaluated the suitability of 3-mm (ID) microporous polytetrafluoroethylene (PTFE) Gore-Tex grafts inserted in the abdominal aorta of eight nonhuman primates (Macaca fascicularis), and the effects of prolonged antiplatelet treatment on both graft patency and the development of intimal hyperplasia in the adjacent vasculature. Four monkeys received antiplatelet medication consisting of aspirin (163 mg twice daily) and dipyridamole (25 mg twice daily). When killed at four months following graft insertion, all four grafts in the antiplatelet medicated group were patent, while in the control group, only two of four grafts were patent. Histologic examination and quantitative photogravitometric evaluation of the degree of luminal narrowing were performed on all grafts and the adjacent vasculature. These studies revealed that while all graft and aortic segments showed varying amounts of intimal thickening, occlusions in the control animals were related to intimal hyperplasia in the host aorta at the site of the distal anastomosis. Intimal hyperplasia in all aortic segments examined distal to the graft was significantly reduced by antiplatelet therapy. Electronmicroscopy showed that smooth muscle cells were the predominant cells of the intimal thickening of the aorta (intimal hyperplasia), and that proliferation of these cells did not extend into the graft itself. The predominant cell population of the intimal thickening of the graft were of the myofibroblast type (neointimal hyperplasis). The luminal surface of the graft was lined with cells that had some but not all of the characteristics of mature endothelial cells. In vitro studies confirmed global interference with platelet function and arachidonic acid metabolism in medicated animals. Medication inhibited platelet cyclo-oxygenase without affecting platelet lipoxygenase, thromboxane synthetase, or prostacyclin-like activity in undisturbed arteries. This study shows that severe intimal hyperplasia develops rapidly in the recipient vessel adjacent to small diameter Gore-Tex grafts, and that the severity of the response is reduced by antiplatelet agents. Histologic examination revealed that the intimal thickening in the graft and the adjacent aortic segments were composed of cells that were not morphologically identical, suggesting two separate aetiologies and the possible need to use different approaches in their prevention.

The effects of insulin on myocardial metabolism and acidosis in normoxia and ischaemia. A 31P-NMR study

1. The effect of insulin on the perfused rat heart during normoxia and total ischaemia was studied by 31P-NMR. 2. During normoxic perfusion, insulin increased the phosphocreatine to ATP ratio at the expense of Pi, when glucose was the substrate. No change was observed when acetate was used as the sole substrate. the intracellular pH (as measured from the position of the 2-deoxyglucose 6-phosphate resonance peak) was unaffected by insulin treatment. 3. Infusion of insulin prior to ischaemia caused an increase in the rate and extent of acidosis during the period of no flow while the rate of ATP depletion was decreased. 4. Freeze-clamped studies showed an increase in glycogen levels upon insulin treatment of the glucose perfused rat heart. During ischaemia, a decrease in glycogen content concomitant with an increase in lactate was observed. The accessibility of glycogen to phosphorylase during ischaemia is increased as a result of insulin treatment. The control of glycolysis during ischaemia is discussed with respect to the content and structure of glycogen in heart tissue.

D-glucose uptake in human liver cell cultures

The kinetics parameters for D-glucose uptake were studied in human liver cell cultures under strictly defined experimental conditions. Using a wide concentration range (0.005 to 30 mmol/l), the kinetic data obtained suggested strongly that D-glucose in human liver cell cultures can be transported by two separate systems. For the high-affinity system, the apparent Km was 0.645 +/- 0.21 mmol/l and the Vmax, 12.49 +/- 3.74 nmol/mg protein per min. For the low-affinity system, the apparent Km was 6.91 +/- 0.58 mmol/l and the Vmax, 79.90 +/- 5.27 nmol/mg protein per min. At a concentration of 2.1 x 10(-7) mol/l, cytochalasin B preferentially inhibited the high-affinity D-glucose site or transport system. The time course of D-glucose uptake, studied in two cell lines from patients with hereditary fructose intolerance, was significantly higher than for the control lines.

Effect of temperature on kinetics and symmetries of the hexose transporter of Novikoff rat hepatoma cells

We have used rapid kinetic techniques to measure the accumulation of radioactively labeled 3-O-methyl-D-glucose to transmembrane equilibrium in Novikoff cell suspensions as a function of temperature. Arrhenius plots of the maximum velocities of isotopic exchange and zero-trans entry were continuous between 6 and 39 degrees C (Ea = 15-19 kcal/mol). Equilibrium exchange and zero-trans entry of 3-O-methyl-glucose at six concentrations (1-30 mM) at 16, 27, and 35 degrees C conformed to appropriate integrated rate equations derived for a single transporter. The hexose transporter exhibited directional symmetry, but the loaded carrier moved about 2 times faster than the empty carrier at all three temperatures investigated. Thus, the differential mobilities of loaded and empty carrier are not affected by temperature in this range. The Michaelis--Menten constant for equilibrium exchange increased about 2-fold with increase in temperature between 16 and 35 degrees C.

Activity of phosphorylase in total global ischaemia in the rat heart. A phosphorus-31 nuclear-magnetic-resonance study

1. The uptake and subsequent phosphorylation of deoxyglucose into perfused rat hearts was monitored by 31P n.m.r. 2. The accumulated deoxyglucose 6-phosphate provided (a) an independent method for measuring cytosolic pH in the normoxic and ischaemic heart tissue and (b) a way of studying the activity of phosphorylase during ischaemia. 3. The cytosolic pH measured from the 31P n.m.r. resonance position of deoxyglucose 6-phosphate is in good agreement under all conditions studied with that obtained previously from the Pi resonances. This eliminates any possible doubts about the use of Pi for measuring intracellular pH. 4. Deoxyglucose 6-phosphate in vitro inhibits phosphorylase b but not phosphorylase a. Its inhibitory effect on glycogenolysis during ischaemia is monitored by measuring tissue acidosis by n.m.r. In the initial stages of ischaemia phosphorylase activity is not inhibited, whereas after about 5 min approx. 50% of the activity is inhibited. These observations are interpreted in terms of the relative contributions of phosphorylase a and the AMP-dependent phosphorylase b activities during ischaemia.

Hexose transport in Novikoff rat hepatoma cells. A simple carrier with directional symmetry, but variable relative mobilities of loaded and empty carrier

The kinetics of transport of the non-metabolizable hexose, 3-O-methyl-D-glucose, have been measured in Novikoff rat hepatoma cells by both zero-trans entry and equilibrium exchange procedures. Transport conformed to a simple carrier model which operates symmetrically with respect to direction, but with greater mobility of the loaded than of the empty carrier. Although a complete kinetic description of the transporter can, in theory, be obtained by application of integrated equations describing the time course of substrate equilibrium across the membrane beginning from the zero-trans situation, statistical analysis of hypothetical data indicated that directional asymmetry or differential mobilities of loaded and empty carrier cannot be discerned reliably from such data alone. The difference in mobility of loaded and empty carrier, apparent in a comparison of zero-trans entry and exchange data, ranged from 1.5--7-fold in different batches of cells. It is concluded that the magnitude of the difference is not an inherent property of the transporter, but is determined physiologically, and may be involved in regulation of hexose transport.

D-Glucose transport across the apical membrane of the surface epithelium in Nereis diversicolor

Epidermal D-glucose transport was investigated in vivo in the brackish-water polychaete worm Nereis diversicolor. Transfer across the apical membrane is rate-limiting to D-glucose uptake, but the cuticle and/or mucus presents some resistance to D-glucose diffusion between bulk solution and transporting membrane. Maximal D-glucose influx is about 10(-12) mol sec-1 per cm2 of apical plasmalemma. Under natural conditions (approximately 1 microM D-glucose in the medium), backflux from the epidermal transport pool is negligible, but a significant paracellular outflux may occur. D-glucose influx across the apical membrane is Na+-dependent and completely inhibitable by phlorizin and harmaline; phloretin is less effective, and cytochalasin B has no effect. Influx is moderately depressed by KCN and iodoacetate, alpha-methyl-D-glucopyranoside is an effective substitute of D-glucose in transport. Animals acclimated to a low salinity, in which epidermal salt transport takes place, show a marked decrease of D-glucose transport capacity. On transfer of animals from a high to a low salinity, or vice versa, the corresponding change of influx occurs after a time-lag of at least an hour. Permeability of the epidermis to simple diffusion of D-glucose is 8 X 10(-8) cm sec-1 (on basis of gross epidermal area).

Inhibition of calcium and glucose uptake by murine leukemia L5178Y cells treated with antiserum

Studies were performed to determine whether decreases in transport of calcium and glucose might be among the earliest changes triggered by the antigen-antibody reactions occurring on the cell surface of murine leukemia L5178Y cells after treatment with rabbit antisera. After treatment with antisera, in the absence of complement, these cells exhibited a decreased uptake of 45Ca, 2-deoxy[3H]glucose, and 3-0-methyl[3H]glucose. These changes occurred rapidly, within 2 minutes after the addition of antiserum, in contrast to the previously reported inhibitory effects of antiserum on DNA, RNA, and protein synthesis, which became demonstrable only after 4 to 8 hours. The kinetics of uptake of the radioactive substrates was biphasic, with a very rapid initial uptake followed by less rapid linear uptake. The precise mechanism of cell growth inhibition remains to be elucidated, but one of the initial effects of antiserum treatment may be a perturbation at the cell membrane such that transport of specific nutrients is decreased, resulting in the observed effects on macromolecular synthesis.

Sugar transport in chick embryo cardiac cells in culture: analysis by countertransport, relationship to phosphorylation and effect of glucose starvation

Embryonic chick heart cells in culture transport 2-deoxy-D-glucose and 3-O-methyl-D-glucose very rapidly. By direct measurements of uptake, it was not possible to estimate accurately transport rates, nor, with 2-deoxyglucose, to discriminate clearly between its transport and phosphorylation. In contrast, the technique of countertransport made it possible to determine precisely initial transport velocity and to make the following observations: (1) phosphorylation, and not transport, is rate-limiting in 2-deoxyglucose uptake; (2) hexose transport is stimulated 5-fold by removal of glucose from culture medium; and (3) this stimulation is followed by an increase in phosphorylation, but the effect is much less pronounced (2-fold stimulation only). In conclusion, the adaptative regulation of glucose transport described in many fibroblast cell lines exists also in cardiac cells.

Lack of correlation between effects of tumor promoter TPA on plasminogen activator production, phosphatidyl choline synthesis, and hexose transport in mammalian cell culture systems

We have investigated the effects of the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) on plasminogen activator production, hexose transport and metabolism, and the incorporation of choline into the acid soluble pool and into phosphatidylcholine in suspension cultures of mouse L, mouse P388 leukemia, human HeLa, and Chinese hamster ovary cells, and in monolayer cultures of baby hamster kidney (BHK), mouse 3T3, mouse 3T6, and mouse P388D1 macrophage-like cells. BHK, 3T3, P388D1, and P388 cells produced plasminogen activator constitutively, but no significant production was observed in the other cell lines. Plasminogen activator production was induced or stimulated by TPA only in P388 cells (10- to 20-fold by 100 ng TPA/ml). On the other hand, phosphatidylcholine synthesis was stimulated by TPA only in HeLa cells, and hexose transport, as measured with 3-0-methyl-D-glucose, only in 3T3 and P388D1 cells, as well as in human lymphocytes. The stimulation of hexose transport occurred more rapidly than the induction of plasminogen activator production and seemed to be part of the mitogenic response of cells to TPA treatment. A stimulation of deoxyglucose uptake was similarly limited to 3T3 and P388D1 cells. A significant decarboxylation of carbon 1 of deoxyglucose occurred in P388 and P388D1 cells, but not in Novikoff cells, and any decarboxylation that occurred was not stimulated by TPA. The results indicate that the various investigated responses of cells to TPA are unrelated and occur independent of each other. The time courses of the biochemical responses also differ significantly.

Inhibition of T cell-mediated cytolysis by 2-deoxy-D-glucose:dissociation of the inhibitory effect from glycoprotein synthesis

Previous studies have established that T cell-mediated cytolysis can be reversibly inhibited by the hexose analogue 2-deoxy-D-glucose (2-DG) by a mechanism which is apparently unrelated to energy depletion. The possibility that the inhibitory effect of 2-DG on cytolysis was linked to its known inhibitory effect on glycoprotein synthesis was therefore investigated. In contrast to the results obtained with 2-DG, no inhibition of cytolysis was observed in the presence of tunicamycin, a potent and specific inhibitor of lipid carrier-dependent protein glycosylation. Furthermore, populations of cytolytic cells which had been pretreated with doses of tunicamycin sufficient to block the incorporation of mannose (or 2-DG) into glycoproteins were still fully susceptible to inhibition by 2-DG. Other known inhibitors of viral protein glycosylation, such as glucosamine and galactosamine, inhibited cytolysis only weakly under conditions where 2-DG was highly effective. Kinetic studies revealed that the inhibitory effect of 2-DG on cytolysis could be reversed within minutes by the addition of exogenous glucose. Furthermore, suggestive evidence was obtained that inhibition cytolysis by 2-DG was linked to a parallel inhibition of effector: target cell binding. Taken together, these results strongly suggest that the inhibitory effect of 2-DG on cytolysis can be dissociated from its effect on protein glycosylation. An alternative mechanism of action of 2-DG is suggested.

Membrane effects of tumor promoters: stimulation of sugar uptake in mammalian cell cultures

Phorbol esters stimulate 2-deoxy-D-glucose (DG) uptake in rodent and human cell cultures. The potent tumor promoting agent, 12-0-tetradecanoyl phorbol-13 acetate (TPA), induces a 12-fold stimulation in confluent 3T3 cells and 2.5-fold stimulation in HeLa cells. When a series of macrocyclic deterpenes are assayed, their relative potencies in stimulating DG uptake in 3T3 cells correlate with other known biologic effects of these compounds. On a molar basis, TPA is a much more potent stimulator of DG transport than insulin or epidermal growth factor. In HeLa cells, the ED50 value of the TPA effect is 0.2 nM. The increase in DG uptake occurs immediately after the addition of TPA, reaches a maximum at 90 minutes, persists for at least three hours after removal of TPA from the medium, and is temperature dependent. The stimulation is not inhibited by cycloheximide or actinomycin D. As in control cells, DG uptake in TPA treated cells is inhibited by p-hydroxymercuribenzoate, phyloridzin, cytochalasin B, and dexamethasone. Although the precise mechanism is not known, evidence is presented that the TPA stimulation of DG uptake is due to enhanced transport of the sugar rather than to effects on intracellular metabolism. The enhanced transport may be secondary to a more generalized change in membrane structure.

Thymidine transport in cultured mammalian cells. Kinetic analysis, temperature dependence and specificity of the transport system

The transport of thymidine has been characterized kinetically and thermodynamically in Novikoff rat hepatoma cells grown in culture and, less extensively, in mouse L cells, Chinese hamster ovary cells, P388 murine leukemia cells and HeLa cells. That the characterizations pertained to the transport system per se was ensured, (i) by employing recently developed methods for rapid sampling of cell/substrate mixtures in order to follow isotope movements within a few seconds after initial exposure of cells to substrate; (ii) by utilizing cells rendered, by genetic or chemical means, incapable of metabolizing thymidine; and (iii) by demonstrating conformity of the transport data to an integrated rate equation derived for a simple, carrier-mediated system. The results indicate that thymidine is transported into mammalian cells by a functionally symmetrical, non-concentrative system for which the carrier : substrate dissociation constant ranges from about 100 microM in Chinese hamster ovary cells, to 230 microM in Novikoff hepatoma cells. In all cell lines investigated, the velocity of transport was sufficient to nearly completely equilibrate low concentration of thymidine across the membrane membrane within 15 s. Temperature dependence of transport velocity and substrate : carrier dissociation were continuous (EA = 18.3 kcal/mol, delta H0' = 9.3 kcal/mol, respectively), and showed no evidence of abrupt transitions. Several natural and artificial nucleosides and nucleic acid bases inhibited influx of radiolabeled thymidine, apparently by competing with thymidine for the transport carrier.

Endogenous cyclic AMP does not modulate transport of hexoses, nucleosides, or nucleobases in Chinese hamster ovary cells

In a previous study we have demonstrated that neither extracellular nor intracellular cyclic adenosine monophosphate (AMP) levels directly affect the uptake of nucleosides, nucleobases, or hexoses by various types of cultured mammalian cells. Uptake of these nutrients into cells, however, involves two processes operating in tandem: facilitated transport across the membrane and intracellular phosphorylation; and uptake rates generally reflect the rates of substrate phosphorylation rather than of transport. In the present study we have examined the question of whether substrate transport per se is regulated by intracellular cyclic AMP. Initially various cell lines, grown both in suspension and monolayer culture, were screened for their cyclic AMP response to prostaglandin E1, isoproterenol, and inhibitors of cyclic AMP phosphodiesterase. Prostaglandin E1 treatment of Chinese hamster ovary cells was selected as the system giving the largest and most consistent (50-fold to 100-fold) elevation of cyclic AMP. Rapid kinetic techniques were used to measure the transport of 3-O-methylglucose, thymidine, adenosine, hypoxanthine, and adenine in wild-type cells and in mutant sublines incapable of phosphorylating these substrates. In no case was an increase in intracellular cyclic AMP accompanied by a significant change in the rate of transport of these substrates, although prostaglandin E1 slightly inhibited the transport of various substrates.