Uptake of 3-O-methyl-D-glucose into cultured human glioma cells

Modulation of glucose uptake in glial and neuronal cell lines by selected neurological drugs

Glucose is the main energy source of brain cells. The transport of glucose across the cell membrane is the first step of its utilization. Any modification in glucose uptake capacity may cause deleterious effects on neural cell functions. In the present study, 3-O-methyl-D-glucose (3-OMG) uptake and its modulation by selected neurological drugs (amitriptyline, selegiline, carbamazepine and phenytoin) were studied in differentiated (with retinoic acid and 12-O-tetradecanoyl phorbol 13-acetate) and undifferentiated neuroblastoma SH-SY5Y and astrocytoma U-373 MG cell lines, using tracer methods. The expression of glucose transporters was studied by immunocytochemistry. SH-SY5Y and U-373 MG cells showed differences both in their glucose uptake properties and in the modulation of glucose uptake by the drugs, which might reflect different specialization of neuronal and glial cells in vivo. While selegiline and amitriptyline had a minor and variable effect on 3-OMG uptake in all cell cultures, the anticonvulsants carbamazepine and phenytoin increased 3-OMG uptake in U-373 MG cells, but decreased that in SH-SY5Y cells. Differentiated SH-SY5Y cells were more sensitive to the effects of the anticonvulsants than undifferentiated SH-SY5Y cells. The results suggest that, the cell lines are promising neural models for the evaluation of drug side effects due to disturbances in glucose uptake.

Transport of L-lactate by cultured rat brain astrocytes

Several reports indicate that lactate can serve as an energy substrate for the brain. The rate of oxidation of this substrate by cultured rat brain astrocytes was 3-fold higher than the rate with glucose, suggesting that lactate can serve as an energy source for these cells. Since transport into the astrocytes may play an important role in regulating nutrient use by individuals types of brain cells, we investigated the uptake of L-[U-14C]lactate by primary cultures of rat brain astrocytes. Measurement of the net uptake suggested two carrier-mediated mechanisms and an Eadie-Hofstee type plot of the data supported this conclusion revealing 2 Km values of 0.49 and 11.38 mM and Vmax values of 16.55 and 173.84 nmol/min/mg protein, respectively. The rate of uptake was temperature dependent and was 3-fold higher at pH 6.2 than at 7.4, but was 50% less at pH 8.2. Although the lactate uptake carrier systems in astrocytes appeared to be labile when incubated in phosphate buffered saline for 20 minutes, the uptake process exhibited an accelerative exchange mechanism. In addition, lactate uptake was altered by several metabolic inhibitors and effectors. Potassium cyanide and alpha-cyano-4-hydroxycinnamate inhibited lactate uptake, but mersalyl had little or no effect. Phenylpyruvate, alpha-ketoisocaproate, and 3-hydroxybutyrate at 5 and 10 mM greatly attenuated the rate of lactate uptake. These results suggest that the availability of lactate as an energy source is regulated in part by a biphasic transport system in primary astrocytes.

The effects of different hexachlorocyclohexanes and cyclodienes on glucose uptake and inositol phospholipid synthesis in rat brain cortex

The inositol lipids from rat brain miniprisms were deacylated and separated by anion-exchange chromatography in order to determine whether or not gamma-hexachlorocyclohexane (gamma-HCH, lindane) and related compounds affect the different phosphatidylinositols. The incorporation of myo-[2-3H]inositol into phosphatidylinositol, phosphatidylinositol monophosphate and phosphatidylinositol bisphosphate were inhibited by lindane and its delta-HCH isomer. The inhibitory effects on phosphatidylinositol synthesis are not prominent in alpha-HCH and they are not significant with the beta-HCH and cyclodienes. The results presented here indicate that the inhibitory effect of lindane and delta-HCH on the phosphatidylinositol metabolism was no exclusively due to an interference with glucose transport. Lindane-treated miniprisms showed decreased myo-[2-3H]inositol uptake and, proportionately, an even greater inhibition of inositol phospholipid synthesis. Cellular uptake can, therefore, not account for all of the lindane inhibition.

Regulation by thyroid hormones of glucose transport in cultured rat myotubes

Primary cultures of skeletal muscle obtained from neonatal rats possess a saturable process for active glucose uptake, the myotubes having a relatively high affinity for the substrate with a Km of 1 mM. The expression of the glucose transport system was most apparent after fusion of single myoblasts to multinucleated myotubes [3-4 days in vitro (DIV)], at which time glucose uptake increased sharply to reach plateau values at about 6-8 DIV. Treatment of the cells at age 6 DIV with triiodothyronine or thyroxine caused a marked increase in glucose uptake beginning 4 h after treatment and reaching a maximum at 24 h. Thyroid hormone-induced increase in glucose uptake was not reduced by either tetrodotoxin or verapamil, thus indicating that the effect was not secondary to the ability of the hormone to increase contractile activity. The effect of thyroid hormones was eliminated completely by inhibition of protein synthesis. The results indicate that thyroid hormones play an important role in regulation of glucose transport in skeletal muscle.

Effects of lindane on the glucose metabolism in rat brain cortex cells

The influence of 0.5 mM gamma-hexachlorocyclohexane (gamma-HCH, lindane) on glucose transport has been investigated using the analog 3-O-methyl-D-(U-14C)glucose. The glucose uptake was lineal for at least 10 sec. Preincubation of dissociated brain cortex cells with lindane decreased the transport of glucose with respect to the controls. The treatment of brain cortex cells with other organochlorine compounds indicated that the alpha-, delta-HCH isomers and dieldrin reproduced the same inhibitory pattern, while beta-HCH and endrin were inactive. The total radioactivity incorporated into CO2 from (U-14C) glucose in the cerebral cortex is also inhibited by lindane in a time dependent manner.

Transport and metabolism of glucose by dissociated brain cells: effects of trypsin

A study was carried out to determine the effect of trypsin on glucose transport into brain cells. Two suspensions of dissociated cells were prepared from the two brain hemispheres of adult rats--one using only mechanical means to dissociate the cells and one using trypsin. The use of trypsin for preparation of dissociated brain cells caused a marked reduction in the rate of transport of [1,2-3H]-2-deoxy-D-glucose compared to uptakes of this glucose analog by cells prepared without trypsin. Responses of the two cell preparations to inhibitors of glucose transport (cytochalasin B and phloretin) were similar. Rates of oxidation of [6-14C]glucose to 14CO2 by trypsin-treated cells were nearly double those in cells prepared without trypsin. Electron microscopic examination of the two preparations revealed much less preservation of structural integrity if trypsin was used to prepare the cells. The findings suggest that trypsin alters cell structure and affects receptor-regulated events in brain cells.

3-O-methyl-D-glucose uptake in isolated bovine adrenal chromaffin cells

The characteristics and regulatory nature of sugar transport in freshly isolated bovine adrenal chromaffin cells were investigated. Transport was measured by following the cell/medium distribution of non-metabolizable glucose analogue, 3-O-methyl-D-glucose. The uptake of 3-O-methyl-D-glucose was was mediated by a saturable transport system with a Km of 8.2 mM and a Vmax of 0.69 nmol/mg protein per min. Basal 3-O-methyl-D-glucose transport was competitively inhibited by D-glucose and a countertransport effect was demonstrated. Cytochalasin B and phloretin, which are specific inhibitors of carrier-mediated glucose transport, significantly decreased basal 3-O-methyl-D-glucose uptake. Basal transport was stimulated by 50 mU/ml insulin, an effect associated with an increase in Vmax. The stimulatory effect of insulin was depressed in medium lacking external Ca2+, or containing the Ca2+-antagonistic ion, La3+, or the Ca2+ channel blocker, methoxyverapamil (D-600). The data suggest that the uptake of 3-O-methyl-D-glucose in freshly isolated bovine adrenal chromaffin cells is mediated by a specific facilitated diffusion mechanism, and is subject to regulation by insulin, thus resembling sugar transport in muscle. In addition, the insulin effect appears to depend on the presence of extracellular Ca2+.

Glucose transport in astrocytes: regulation by thyroid hormone

Primary cultures of astrocytes from newborn rat brain showed evidence of a substrate-saturable process for glucose transport. The system shows a relatively high affinity for the substrate, with an apparent Km of approximately 1 mM. Maintenance of the cells in medium containing thyroid-hormone-free serum for 3, 6, or 9 days resulted in significantly reduced rates of hexose transport. Addition of exogenous triiodothyronine to the transport incubation medium of these "hypothyroid" cells markedly increased the net rate of 2-deoxyglucose uptake within 60 s to values equal to or above those of control cultures (cells maintained in normal serum). These findings support a key role for thyroid hormone in the transport of glucose across plasma membranes of brain cells and demonstrate the presence of this regulatory system in astrocytes.

Transport of 2-deoxy-D-glucose by dissociated brain cells

The characteristics of glucose transport into dissociated cells from rat brain were determined using [1,2-3H]2-deoxyglucose as substrate. The rate of net uptake exhibited biphasic saturation kinetics with increasing substrate concentration; two values each for Km (8.85 and 1.05 mM) and Vmax (20.41 +/- 5.99 nmol/min/mg protein) were obtained, indicating the presence of two transport systems. D-glucose competed with [1,2-3H]2-deoxyglucose as shown by increasing degrees of inhibition of uptake of labeled substrate with increasing concentrations of D-glucose. The presence of an accelerative exchange mechanism was demonstrated by enhanced rates of uptake of labeled substrate by cells pre-loaded with high levels of unlabeled 2-deoxyglucose. Transport was inhibited by cytochalasin B, phloretin and phloridzin in a manner suggesting that the system is sodium-independent. Transport was also inhibited by sodium cyanide, potassium cyanide and dinitrophenol, but not by sodium arsenite or ouabain. Insulin status of the animals had no effect on the rate of transport of this substrate. Net transport was significantly lower in neonatal (4-day-old) rats than in either older sucklings (14-16-day-old) or adult animals; no significant difference between the latter two groups was observed. These findings demonstrate that two carrier-mediated systems for glucose transport are present on the membranes of these mixed brain cells suggesting that the kinetic characteristics of glucose transport may differ between neurons and glial cells. The age change in transport rate may reflect age-associated glial cell proliferation and/or an age-dependent increase in the number of transporters per cell in one brain cell type.

Unidirectional influx and phosphorylation of glucose analogues in cultured astroblasts

Unidirectional influx of 14C-3OMG (3-O-methyl-D-glucose) and rate of phosphorylation of 14C-2DG (2-deoxy-D-glucose) were determined in primary cultures of astroblasts under conditions with negligible unstirred layers. The influx exhibited rate constants between 7.2 and 8.3 min-1 in the concentration range 2.5-25 mM of unlabeled 3OMG and was considered constant, irrespective of concentration of 3OMG. The rate of phosphorylation of 14C-2DG declined for rising concentrations of 2DG and hence showed saturability. The rate constants ranged from 7.9 to 0.1 min-1 in the concentration range 0.04-25 mM of 2DG. These results are not consistent with the view that the influx limits the rate of phosphorylation. They support the notion that the influx is not rate limiting for the phosphorylation.

Substrate oxidation by isolated rat brain mitochondria and synaptosomes

The rates of [6-14C]-glucose oxidation by reconstituted systems of cytosol and mitochondria or cytosol and synaptosomes were essentially the same as the rate of oxidation of [3-14C]-3-hydroxybutyrate. However, the rate of [U-14C]-glutamine oxidation by mitochondria was 2.5 times that by synaptosomes. The addition of glutamine (5 mM) caused a reduction in the rates of oxidation [6-14C]-glucose of 20% and 40% by mitochondria and synaptosomes, respectively. Conversely, the addition of glucose (5 mM) had little or no effect on the rate of [U-14C]-glutamine oxidation by either organelle. Amino-oxyacetate decreased [U-14C]-glutamine oxidation by mitochondria more than 35% but had little or no effect on the rate of glutamine oxidation by synaptosomes. When glucose (5 mM) was added to [3-14C]-3-hydroxybutyrate, the rates of oxidation by the mitochondria and synaptosomes were increased by 65% and 77%, respectively. However, in the reverse situation the addition of 3-hydroxybutyrate decreased [6-14C]-glucose oxidation by synaptosomes (35%) but did not decrease the rate by mitochondria. These results suggest that differences in the rates of substrate utilization by mitochondria and synaptosomes and differences in substrate interactions in these two subcellular organelles may contribute to metabolic compartmentation in the brain.

Rapid cellular regulation of D-glucose transport in cultured neural cells

Previous studies have revealed two different kinds of regulation of glucose utilization in cell lines derived from the nervous system (Keller et al., 1981). We found glucose metabolism of C-6 glioma cells to be limited and regulated by membrane transport. In contrast, glucose utilization of C-1300 neuroblastoma (N2A) cells was limited by the known regulatory enzymes of the Embden-Meyerhof pathway. Under the given experimental conditions the "membrane-limited" C-6 glioma cells were characterized by periodically changing glucose transport rates and very low intracellular glucose concentrations, which remained constant in spite of widely differing transport rates. These findings suggest the close functional coupling between transport and phosphorylation required for the regulation of glucose transport by cellular metabolic needs.

3-O-methylglucose transport in internally dialysed giant axons of Loligo

1. The transport of the non-metabolized sugar, 3-O-methylglucose, has been studied in the squid axon under conditions where the intracellular environment of the axon is controlled by internal dialysis. 2. Sugar transport is passive, shows saturation kinetics and is asymmetric. At 15 degrees C, the Michaelis and velocity constants for exit are approximately four times those for uptake. The asymmetry of transport is increased by raising the temperature. 3. Sugar uptake is not affected by intracellular sugar levels as high as 100 mM. Sugar exit is, however, reduced by external sugars although the apparent Km for exit is unaffected. 4. The kinetics of sugar exit under exchange conditions are determined by the kinetics of sugar uptake. These results can be accounted for by the asymmetric mobile-carrier and simultaneous-carrier models for transport. 5. Both sugar uptake and exit are reduced in the absence of ATPi. Kinetic analysis of transport under these conditions show that the capacity of the system to transport sugar is unchanged but that the affinity of the system for sugar is reduced. Internal cyclic AMP, AMP, ADP or GTP (2 mM) do not mimic this action of ATP. The hydrolysable analogue of ATP, alpha, beta-methylene-5-ATP (2 mM), (but not the nonhydrolysable analogue beta, gamma-methylene-5-ATP, 2 mM) has an ATP-like action on sugar transport. 6. Transport is unaffected by internal Ca2+ concentrations in the range 4 X 10(-8)--9 X 10(-7) M.

Growth dependent induction of high affinity gamma-amino-butyric acid transport in cultures of a normal human brain cell line

Dense, growth inhibited cultures of the human putative glial cell line U-787CG were found to take up gamma-aminobutyric acid (GABA) via a high-affinity transport mechanism (Km = 1.2 microM) not detectable in sparse, rapidly growing cultures. The uptake of GABA was essentially the same in young and old dense cultures indicating that the induction of the high-affinity GABA transport was dependent on cell density and/or growth rate rather than time in culture after trypsinization.

D-Glucose transport in cultured cells of neural origin: the membrane as possible control point of glucose utilization

The function of plasma membrane as control point of glucose metabolism has been studied in confluent monolayer of C1300 neuroblastoma (N2A) and glioma (C6) cells. In neuroblastoma, steady state intracellular glucose concentration reached the extracellular levels, while intracellular contents in C6 glioma cells remained very low. In C6 glial cells the amount of glycogen as source of energy was much higher than that found in C1300 neuroblastoma cells. Influx rates of D-glucose in C6 glioma cells were only half those found in neuroblastoma cells. During the influx period (0-40 s) the transport of glucose in these cells did not exceed the phosphorylation rate, whereas a steady, time-dependent increase in glucose content was observed in neuroblastoma cells. While glucose uptake in neuroblastoma cells seems to be regulated at the level of phosphorylating enzymes, the control point in C6 glioma is believed to be membrane transport.

Increased activity of a phospholipid base-exchange system by the differentiation of neoplastic cells from the nervous system

The activity of a base-exchange enzyme system, specific for the polar head-groups of brain phospholipids, was measured in both C 1300 mouse neuroblastoma (clone 41A3) and human glioma 138 MG cell lines. This base-exchange is thought to occur between free nitrogenous bases and membrane-bound phospholipids. The incorporation of free 14C-labeled ethanolamine and L-serine was determined in undifferentiated and morphologically differentiated cells. Both cell lines showed a significant increase in ethanolamine and L-serine incorporation upon differentiation.

Drug-induced differentiation of a rat glioma in vitro: II. the expression of S-100, a glial specific protein and steroid sulfatase

Amethopterin and 5-bromodeoxyuridine (BUdR) were used to induce morphological changes in cloned rat glioma (C6). The expression of S-100 protein, an acidic protein localized in glial cells, and steroid sulfatase, an ubiquitously distributed enzyme found in high concentration in glial cells, were followed during cell growth, from subculture to well into the stationary phase of control and drug-treated cultures. Amethopterin and BUdR differed in their effects on glioma morphology and in the expression of the biochemical parameters. Amethopterin coordinately stimualted both the production of S-100 protein and steroid sulfatase activity when cell division was inhibited during early logarithmic growth phase. BUdR stimulated steroid sulfatase activity but repressed production of S-100 protein. The results are discussed with respect to the mechanism of regulation of the differentiated state of tumor cells.

Uptake of radiolabeled glucose analogues by organotypic cerebellar cultures

Permeability of brain cells to radiolabeled glucose analogues with sucrose or inulin or L-glucose was studied in the living, intact state of the organotypic cerebellar cultures. In vitro uptake of 3H 3-O-methyl D-glucose and 3H 2-deoxy-D-glucose exhibited saturation kinetics with increasing substrate concentrations. Each of the labeled sugars uptake could be self-inhibited in the presence of unlabeled (cold) substrate and cross-inhibited with cold glucose or xylose or phlorizin present in the incubating medium. The uptake was Na-independent and stereo-specific for D-form.

Cytochalasin B inhibition of brain glucose transport and the influence of blood components on inhibitor concentration

The effect of cytochalasin B on cerebral glucose transport and metabolism was investigated in 19 isolated perfused dog brain preparations. Cytochalasin B is a potent, non-competitive inhibitor of glucose transport at the blood-brain interface. Both glucose transport into (Ki = 6.6 +/- 1.9 micrometer) and out of the capillary endothelial cell are inhibited. The inhibition is readily reversible by perfusion with blood containing no cytochalasin B. After 2 min of exposure to 30 micrometer cytochalasin B, the cerebral oxygen consumption decreases by 31% probably due to decreased availability of glucose for oxidative metabolism. About one-half of the cytochalasin B that is dissolved in blood is bound to erythrocytes and other blood components while the remainder is free.