Enzymes of glucose metabolism in cultured human gliomas: Neoplasia is accompanied by altered hexokinase, phosphofructokinase, and glucose-6-phosphate dehydrogenase levels

Abstract

The enzymes of glycolysis and selected enzymes of the pentose phosphate pathways were measured by fluorometric methods in extracts prepared from cultures of normal cortical human astrocytes and from cultures derived from low-grade (II) or high-grade (IV) gliomas. The hexokinase and phosphofructokinase levels of the low-grade glioma-derived line were not significantly different from those of the normal astrocyte cultures. However, the activities of hexokinase and phosphofructokinase were consistently and significantly increased in the high-grade glioma-derived lines. The activity of glucose-6-phosphate dehydrogenase was significantly decreased in all glioma-derived lines and by more than 90% in the high-grade-derived lines. Other enzymes of the glycolytic pathway were not significantly different from those of normal astrocytes, or they showed a variation inconsistently related to the neoplastic state. Glucose flux is not apparently regulated to a significant degree of hexokinase in glioma-derived lines, since the measured Vmax values are in substantial excess over the measured flux rates. Reversible binding of hexokinase to the particulate fraction was observed in both the normal astrocytes cultures and the high-grade glioma-derived lines. A twofold displacement of particulate hexokinase by ATP, ADP, 1-O-methylglucose, sorbitol-6-phosphate, and dibutyryl cyclic AMP was observed in the high-grade glioma-derived lines. The degree of displacement by various agents and the basal ratio of free/bound was not significantly different between the transformers and the nontransformants. The hexokinase from both the gliomas and the normal astrocytes was noncompetitively inhibited by the glucose analogue 2-deoxy-d-glucose. Phosphofructokinase activity is close to the observed glucose flux rates in both the normal astrocyte and the glioma-derived cultures. The phosphofructokinase activity of normal astrocytes is activated twofold or more by ADP, AMP, fructose-2,6-diphosphate, and Pi. However, these same ligands activate phosphofructokinase by less than twofold in a typical high-grade glioma-derived line. ATP, dibutyryl cyclic AMP, and citrate inhibit glioma and normal astrocytic phosphofructokinase, but the magnitude of the inhibition is much less than in the glioma-derived lines.

Changes in glucose uptake by malignant gliomas: preliminary study of prognostic significance

“…Glucose consumption is highest among the more biologically malignant and rapidly growing cells. Furthermore, in tissue culture, glioma demonstrates phenotypic changes in the regulatory enzymes of glycolysis, specifically hexokinase and phosphofructokinase, which are consistent with the observed increase in glycolytic rate [21]. In addition, the pentose phosphate pathway in cultured human derived glioma is increased approximately 400% compared to normal astrocytes [22].…”

“…Gliomas, like other malignant neoplasms, possess an accelerated intermediary metabolism as an expression of their transformed state [19][20][21][22]. The rCMRGlu of gliomas, as measured by PET-FDG, and the rate of glucose consumption by cultured cells derived from those tumors are closely correlated [2,28].…”

“…Accordingly, the increased rCMRGlu might represent acceleration of aereobic glycolysis and cellular respiration in order to raise the levels of nucleoside triphosphates (NTP) within the tumor and thus increase its bioenergetic state [16][17][18]. Accelerated shunting of glucose through the phosphogluconate pathway could also increase the levels of reduced nicotinamide adenine dinucleotide phosphate (NADPH) in the neoplasm to maintain an adequate oxidation-reduction balance and scavenge free radicals produced by the cytotoxic drugs [11,[19][20][21][22]. Salvage pathways for nucleoside synthesis could also be activated through the phosphogluconate shunt [19,20].…”

Glycolytic glioma cells with active glycogen synthase are sensitive to PTEN and inhibitors of PI3K and gluconeogenesis

“…Once 2DG is transported into cells and phosphorylated, it is trapped intracellularly and inhibits hexokinase. [41][42][43] Glycogenolysis of glycogen with incorporated 2DG is also inhibited. 42,44 Metformin (MF), or 1,1-dimethylbiguanide, a clinical drug that inhibits gluconeogenesis, 45,46 was dissolved in phosphate-buffered saline (PBS) for testing in migration assays.…”

Effects of 2-Deoxy-d-Glucose on Proliferation of Vascular Smooth Muscle Cells and Endothelial Cells

“…2,3 Increases in glucose transport and the activities of hexokinase, phosphofructokinase and pyruvate kinase were suggested to be responsible for the increased flux of glucose through the Embden-Meyerhof pathway in cancer cells. 4 2-Deoxy-D-glucose (2-DG) is a glucose analogue that is capable of inhibiting glycolysis and glycosylation. Due to its missing hydroxyl group at the second carbon position, this substance can irreversibly block key enzymes of the Embden-Mayerhof pathway.…”