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PubMed1987

Effect of lonidamine on the utilization of 14C-labeled glucose by human astrocytoma cells.

The effect of lonidamine (LND), 1-(2,4-dichlorobenzyl)-1H-indazol-3 carboxylic acid, on the utilization of carbon from 14C-labeled glucose by cell cultures of the permanent strain LI derived from a human glioblastoma multiforme (astrocytoma) has been investigated. The results may be summarized as follows. Aerobic glycolysis is the main energy-yielding process as shown by the fact that the greatest part of glucose carbon atoms is incorporated into lactate. Nevertheless, the amount of glucose converted accounts for only 63% of the lactate produced, indicating the presence of an elevated endogenous aerobic glycolysis. The amount of glucose carbon atoms incorporated into CO2, lipids, nucleic acid, and supporting structures is low. LND decreased the incorporation of 14C activity in all the above mentioned isolated compounds because of its ability to inhibit glucose phosphorylation. Consequently, there is a lower concentration of glucose-6-phosphate which, in turn, affects the rate of formation of several metabolites in glycolytic and pentose phosphate pathways. Experiments with [1-14C]-2-deoxy-D-glucose further substantiate the idea of glucose phosphorylation as a main target of LND and strongly suggest the presence of a mitochondrially bound hexokinase. The higher inhibition of glucose phosphorylation in exponentially growing cells indicates a further shift of the enzyme toward mitochondria-bound form and confirms the importance of the energy status of the cell in eliciting the response to LND. The reduced capacity of LND-treated cells to synthetize ATP and glucose-6-phosphate reflects the decreased synthesis of proteins and nucleic acids, which affects cell growth and duplication.

Antineoplastic Agents↗

PubMed1985

Stimulation of the hexose monophosphate pathway by pyrroline-5-carboxylate reductase in the lens.

Addition of pyrroline-5-carboxylate (P5C) or its precursors to rat lenses cultured for 24 hr in TC-199 medium containing 14C-glucose results in an apparent concentration-dependent increase in hexose monophosphate-pentose (HMP) pathway activity. Addition of proline, the reduction product of P5C, did not result in an increase, suggesting that stimulation of the HMP pathway is related to the reduction of P5C to proline by the enzyme P5C reductase. No apparent feedback inhibition on P5C reductase was observed. Stimulation of HMP pathway activity by P5C was also observed in the lenses of Philly and Nakano mouse, two models of congenital osmotic cataracts. Compared with its genetic control, the Swiss--Webster mouse, generally no difference in the lenticular levels of HMP pathway activity was observed in the Philly mouse--even after the onset of cataract. Stimulation of the HMP pathway in the Philly lens by P5C, however, was consistently lower than its control. In the lenses from the Nakano mouse and its genetic control, the Balb/c mouse, no difference in the percentage stimulation of the HMP pathway resulting from the addition of P5C was observed, but HMP pathway activity in the Nakano lens was consistently lower than that of the control.

Aging↗

PubMed1984

Specificity of the rat hepatocyte monosaccharide transporter.

The effect of a number of hexoses and pentoses on 3-O-methyl-D-glucose transport into isolated hepatocytes is reported. The hexoses tested inhibited transport in a competitive manner, with Ki values ranging from 80 to 190 mM. No significant inhibition was seen with either D-ribose or D-arabinose.

3-O-Methylglucose↗

PubMed1994

Glucose metabolism in separated embryos and investing membranes during organogenesis in the rat.

Glucose metabolism provides an essential energy source in the mammalian embryo. We used the rat embryo culture system to investigate the activity of several critical pathways for glucose metabolism during early organogenesis, before (day 10 of gestation) and during (day 11) the establishment of the chorioallantoic circulation and closure of the neural tube. We studied glucose metabolism in the intact conceptus, the separated embryo, and its investing membranes, including the visceral yolk sac, allantois, and amnion. Short-term incubations were performed for 4 hours in culture media containing U-14C-, 14C-1-, or 14C-6-labeled D-glucose on day 10 and day 11 of gestation, and the rates of glucose utilization by glycolysis and oxidative metabolism, including the pentose phosphate pathway (PPP), were measured. Glycolytic metabolism, estimated by the accumulation of lactate, was high on day 10 in the intact conceptus, embryo, and membranes (92 +/- 6, 63 +/- 5, and 99 +/- 8 nmol/micrograms protein/4 h, respectively) and decreased by two thirds by day 11 in each tissue. Of note, the rate of glycolysis was greater in membranes than in the embryo on both days (P < .01). On the other hand, oxidative metabolism, reflected in the production of 14CO2, was relatively low on day 10 (0.78 +/- 0.04, 0.73 +/- 0.05, and 0.6 +/- 0.06 nmol/micrograms protein/4 h for intact conceptus, embryo, and membranes, respectively) and increased significantly in each tissue by day 11 (P < .01 for each).

Animals↗

PubMed1991

Metabolic changes of several adipose depots as caused by aging.

In this study, metabolic changes of several adipose depots as caused by aging were investigated. Key enzyme activity of glutaminolysis, pentose-phosphate pathway and Krebs cycle were measured. The rates of lipogenesis from 3H2O, lipoprotein lipase (LPL) activity and rate of lipolysis in vitro were also determined. The results obtained indicate a reduced capacity for lipogenesis in several adipose depots by aging. The authors concluded that hypertrophy of adipose tissue reported during aging is possible due to increased LPL activity and reduced rate of lipolysis.

Adipose Tissue↗

PubMed1994

Changes in pancreatic islets in aging Wistar and Zucker rats: a histochemical and ultrastructural morphometric study.

Morphometrical and cytochemical techniques have been applied to characterize the islets of Langerhans tissue in lean and obese Zucker fa/fa and Wistar rats. The changes in cytologic composition correlated with levels of serum glucose and lipids in obese rats and progressed significantly with increasing body weight. Histochemical and enzyme abnormalities observed in Zucker fa/fa and Wistar rats reflect the degenerative and reactive processes in the pancreas: a decrease in Krebs cycle and pentose pathway and increased lysosomal acid phosphatase reflect the degeneration of the islets. Changes consisted of pronounced insulin cell hyperplasia and disruption of islet architecture. The raised functional activity in the islet B-cells of the Zucker fa/fa and Wistar rats was reflected in enlargement and fragmentation of the Golgi apparatus. An increased proportion of light granules is associated with increased insulin secretion, which reinforces the idea that light granules are responsible for immediate insulin secretion, whereas the dark granules represent the insulin stored in the cell for a longer period The islets of Langerhans of the Zucker fa/fa and Wistar rats show marked differences in morphological, histochemical and morphometrical characteristics when compared with littermates. There is a marked difference in insulin secretion between the obese Zucker fa/fa and Wistar rats and its non-obese littermate. These differences may be related to the development with obesity of aging and genetically-conditioned animals.

Aging↗

PubMed1994

Cobalt and possible oxidant-mediated toxicity.

The occurrence of interstitial lung disease similar to hard metal lung disease in diamond polishers who had been exposed to cobalt (in the absence of tungsten carbide) through the use of polishing disks containing microdiamonds sintered with cobalt, led us to experimentally test the hypothesis that cobalt has pro-oxidant activity in lung tissue. Several experiments were carried out in which we measured indices of oxidant stress, mainly changes in the oxidation state of glutathione and in the activity of the pentose phosphate pathway, upon exposure of hamster pulmonary tissue to CoCl2 in vivo by intratracheal instillation, or in vitro by incubating lung slices. These experiments indicated that cobalt ions are capable of causing thiol oxidation in lung tissue as an early manifestation of oxidant stress, but more studies are needed to establish the relevance of this mechanism in the causation of lung disease in subjects exposed to cobalt-containing dusts.

Animals↗

PubMed1996

Hemolytic anemias due to erythrocyte enzyme deficiencies.

Red blood cells can only fulfil their functions over the normal period of approximately 120 days with 1.7 x 10(5) circulatory cycles efficiently if they withstand external and internal loads. This requires ATP and redox equivalents, which have to be permanently regenerated by the energy and redox metabolism. These pathways are necessary to maintain the biconcave shape of the cells, their specific intracellular cation concentrations, the reduced state of hemoglobin with a divalent iron and the sulfhydryl groups of enzymes, glutathione and membrane components. If an enzyme deficiency of one of these metabolic pathways limits the ATP and/or NADPH production, distinct membrane alterations result causing a removal of the damaged cells by the monocyte-macrophage system. Most metabolic needs of erythrocytes are covered by glycolysis, the oxidative pentose phosphate pathway (OPPP), the glutathione cycle, nucleotide metabolism and MetHb reductase. Hereditary enzyme deficiencies of all these pathways have been identified; those that cause non-spherocytic hemolytic anemia are listed in Table 4. Their frequencies differ markedly both with respect to the affected enzyme and geographic distribution. Glucose-6-phosphate dehydrogenase enzymopathies (G6PD) are with more than 400 million cases by far the most common deficiency. The highest gene frequency has been found with 0.7 among Kurdish Jews. G6PD deficiencies are furthermore prevalent with frequencies of about 0.1 among Africans, Black Americans, and populations of Mediterranean countries and South East Asia. In Middle and Northern Europe the frequency of G6PD is much lower, and with approximately 0.0005, comparable with the frequency of pyruvate kinase (PK) enzymopathies, the most frequent enzyme deficiency in glycolysis in this area (Luzzatto, 1987; Beutler and Kuhl, 1990). The relationship between the degree of enzyme deficiency and the extent of metabolic dysfunction in red blood cells and other tissues depend on several factors: on the importance of the affected enzyme; its expression rate; the stability of the mutant enzyme against proteolytic degradation and functional abnormalities; the possibility to compensate the deficiency by an overexpression of the corresponding isoenzyme or by the use of an alternative metabolic pathway. Difficulties in estimating the quantitative degree of disorder in severe cases are due to the fact that these populations contain many reticulocytes, which generally have higher enzyme activities and concentrations of intermediates than erythrocytes. An alternative approach to predict metabolic changes is the analysis by mathematical modeling. Mathematical modeling of the main metabolic pathways of human erythrocytes has reached an advanced level (Rapoport et al., 1976; Holzhütter et al., 1985; Schuster et al., 1988). Models have been successfully employed to describe stationary and time-dependent metabolic states of the cell under normal conditions as well as in the presence of enzyme deficiencies. Figure 5 shows computational results of erythrocyte enzyme deficiencies. This analysis is based on the comprehensive mathematical model of the energy and redox metabolism for human erythrocyte presented in Fig. 6. Stationary states of the cell metabolism have been calculated by varying the activity of each of the participating enzymes by several orders of magnitude. To predict consequences of enzyme deficiencies a performance function has been introduced (Schuster and Holzhütter, 1995). It takes into account the homeostasis of three essential metabolic variables: the energetic state (ATP), the reductive capacity (reduced glutathione) and the osmotic state. From the data given in Fig. 5 one can conclude that generally the metabolic impairment resulting in deficiencies occurs earlier for enzymes with high control coefficients than for those catalyzing equilibrium reactions. On the other hand the flux curves of latter enzymes decrease more steeply below a critica

Anemia, Hemolytic↗

PubMed1994

Purine metabolism in promyelocytic HL60 and dimethylsulphoxide-differentiated HL60 cells.

Purine metabolism was studied in the human promyelocytic leukaemic cell line HL60 both before and after differentiation by dimethylsulphoxide (DMSO) treatment in vitro. DMSO-induced differentiation had no effect on the steady-state concentration of 5-phosphoribosylpyrophosphate (PRPP), even though the activity of the oxidative segment of the pentose phosphate pathway (OPP) increased two-fold and the activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were enhanced 3-6 times. [14C]-formate incorporation, on the other hand, showed that undifferentiated HL60 cells produced purines by the de novo pathway at six-fold the rate of the differentiated cells and at three times the rate measured in polymorphonuclear leukocytes (PMNs) separated from human blood. This is consistent with significantly higher activities (two to five-fold) of the key regulatory enzymes of the de novo purine synthesis pathway (PRPP synthetase, amido-phosphoribosyl transferase and adenylosuccinate synthase) in the undifferentiated cells. Labelling the cells with [14C]-hypoxanthine showed that there was an active salvage pathway in the HL60 cells which remained unaltered by differentiation. The activities of the salvage enzymes were also the same, although hypoxanthine was taken up at twice the rate by the undifferentiated cells. Human PMNs had an active salvage pathway, but their rate was five times lower than that of the HL60 cells, consistent with much lower activities (three to eight-fold) of the salvage pathway enzymes. These observations suggest that regulation of the synthesis and activities of the purine nucleotide synthesis enzymes may play an important role in the regulation of differentiation of myeloid cells.

Cell Differentiation↗

PubMed1991

Selective stimulation of in situ intermediary metabolism by free calcium in permeabilized rat adipocytes.

The hypothesis that ionized calcium [Ca2+]i may stimulate in situ rat adipocyte intermediary metabolism distal to glucose transport was tested. A metabolically active porous adipocyte model was employed in which pathway metabolism is exclusively pore-dependent using glucose 6-phosphate (G6P) as substrate. Cellular [Ca2+]i was, furthermore, directly adjusted to between 0-2.5 microM via the membrane pores. Three metabolic fluxes were examined, (1) glycolysis-Krebs ([6-14C]G6P oxidation), (2) glycolysis to lactate ([U-14C]G6P to [14C]lactate) and (3) pentose pathway ([1-14C]G6P oxidation). Glycolysis-Krebs oxidation was was found to be selectively (33% above basal P less than 0.001) stimulated by 0.625 microM free calcium. In contrast, there was no effect of [Ca2+]i on the other, exclusively cytoplasmic, pathways. The stimulation of glycolysis-Krebs by [Ca2+]i was inhibited by a mitochondrial calcium channel blocker (Ruthenium red) and persisted over a range of ATP/ADP ratios. Separate studies demonstrated that 2-[1-14C]ketoglutarate oxidation was also calcium-stimulated in the porous adipocytes (160% over baseline at 1 microM [Ca2+]i). These studies thus demonstrate that physiologically relevant increments in porous adipocyte [Ca2+]i enhance overall in situ glycolytic-Krebs pathway oxidation by a mechanism which entails mitochondrial calcium uptake. Methodologically, this metabolically active porous adipocyte model presents a novel experimental approach to investigations regarding the effects of ionized calcium on intermediary metabolism beyond glucose transport.

Adipose Tissue↗

PubMed1994

Control of glucose metabolism in newborn pig enterocytes: evidence for the role of hexokinase.

The objective of the present work was to identify the regulatory step(s) in the post-natal development of a high glycolytic capacity previously evidenced in newborn pig enterocytes (Darcy-Vrillon et al. (1994) Pediat. Res., 36, 175-181. Glucose entry via the Na+/glucose cotransporter, estimated by the uptake of the non-metabolizable analogue methyl alpha-D-[U-14C]glucopyranoside, slightly decreased between birth and 2 days of sucking. The flux of glucose metabolized into the pentose cycle pathway slightly increased but could not account for the 3-fold increase observed in the glycolytic capacity. Whereas the maximal activity of 6-phosphofructo-1-kinase did not change between stages, there was a significant increase in hexokinase activity as well as in the flux of glucose phosphorylated. These findings suggest that the stimulation of glucose phosphorylation through hexokinase is the key event leading to an increased glycolytic capacity of small intestinal cells at the onset of sucking.

Animals↗

PubMed1991

Metabolism of glucose, glutamine, long-chain fatty acids and ketone bodies by lungs of the rat.

The maximum activities of some key enzymes of metabolism were studied in lungs of fed and 48-h-starved rats. The maximum activity of hexokinase in the lung is similar to that of other tissues of the body, but lower than that of phosphorylase and 6-phosphofructokinase. High activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were found in lung tissue, suggesting the importance of the pentose phosphate pathway in the lung. The activities of hexokinase and 6-phosphofructokinase were decreased whereas that of phosphorylase increased in response to starvation. Of the enzymes of the tricarboxylic acid cycle whose activities were measured, that of oxoglutarate dehydrogenase was the lowest, yet its activity (approximately 4.2 nmol/min per mg protein at 37 degrees C) was considerably greater than the flux through the cycle (0.46 nmol/min per mg protein at 37 degrees C; calculated from oxygen consumption by incubated lung slices). The activities of both oxoglutarate dehydrogenase and citrate synthase were decreased by starvation. The activities of 3-oxoacid CoA-transferase and acetoacetyl-CoA thiolase were low in lung tissue compared to those of other tissues (eg kidney, brain) and that of 3-hydroxybutyrate dehydrogenase was very low. The activity of carnitine palmitoyl transferase is higher in the lung, suggesting that fatty acids (and possibly acetoacetate) could provide acetyl-CoA as substrate for the tricarboxylic acid cycle. Very low rates of utilization of 3-hydroxybutyrate were observed during incubation of lung slices, but that of oleate was 1.2 nmol/h per mg of protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

31P nuclear magnetic resonance (NMR) identification of sugar phosphates in isolated rat ovarian follicular granulosa cells and the effects of follicle-stimulating hormone.

Immature female rats (23-30 days old) were implanted subcutaneously with diethylstilbestrol (DES) in silastic capsules. After 48 h their ovaries were removed and the granulosa cells isolated (Foreman et al. (1984) Life Sci. 35, 1273-1279). The cells were incubated in Hepes balanced saline buffer with substrates with or without follicle-stimulating hormone (FSH). At the end of incubation perchloric acid extracts were made for 31P NMR spectroscopy. The resonances of fructose 1-phosphate, fructose 6-phosphate, glucose 1-phosphate, and ribose 5-phosphate were identified in the granulosa cell extracts. The relative intensities of fructose 6-phosphate to ribose 5-phosphate decreased after incubation with FSH in vitro. This suggests that FSH increases the activity of the pentose pathway within 1 h. Thus, FSH can acutely activate those metabolic pathways which provide nicotinamide-adenine dinucleotide phosphate (NADPH) to be used in steroid synthesis and cholesterol mobilization.

Animals↗

PubMed1984

Inhibition of 6-phosphogluconate dehydrogenase by glucose 1,6-diphosphate in human normal and malignant colon extracts.

Increased activity of 6-phosphogluconate dehydrogenase was found in human colon tumors as compared to the adjacent unaffected mucosa. Glucose 1,6-diphosphate (Glc-1,6-P2), an endogenous potent regulator of glucose metabolism, markedly inhibited the activity of 6-phosphogluconate dehydrogenase (6-PGD) in extracts of the normal and malignant human colon. Glc-1,6-P2 also inhibited the activity of hexokinase in these extracts. The endogenous levels of Glc-1,6-P2 in the colon and tumors were measured. Since the pentose cycle can be inhibited by Glc-1,6-P2, means to increase endogenous levels of Glc-1,6-P2 or to introduce it into cells, might result in antitumor effects.

Colonic Neoplasms↗

PubMed1979

Effects of acute starvation on carbohydrate metabolism in rat salivary glands.

1. Effects of acute starvation on enzymes of carbohydrate metabolism were determined in rat submandibular and parotid glands. 2. Activities of glycolytic enzymes were high in submandibular gland, but those of pentose phosphate pathway and glycogen metabolism were high in parotid gland. 3. Enzyme activities were lowered by acute starvation. Refeeding the rats with solid diet restored the enzyme activities, but with liquid diet, only partial recoveries were found in submandibular gland.

Animals↗

PubMed1987

Heterogeneity of regional cerebral glucose metabolism demonstrated in situ in rat brain by 19F NMR rotating frame zeugmatography: one dimensional chemical shift imaging of normal and gliosarcoma implanted brain.

Using 19-fluorine (19F) as nuclear magnetic resonance (NMR) signal probe and 2-fluoro-2-deoxy-D-glucose (2-FDG) as metabolic probe, one dimensional "imaging" (metabolite mapping) of pathway specific glucose metabolism in the pentose monophosphate shunt (PMS) and aldose reductase sorbitol (ARS) pathways were performed in situ in rat brain utilizing one dimensional rotating frame zeugmatography. Normal brain showed highest PMS activities in the brainstem consonant with known spatially heterogeneous concentration of glucose-6-phosphate dehydrogenase, the rate limiting enzyme for the PMS. The brain harboring sufficiently large gliosarcoma in the cerebrum showed a higher PMS/ARS area ratio indicating higher PMS activities in tumor which was localized by zeugmatography. The present study demonstrated the feasibility of studying regional glucose metabolism in the PMS and ARS utilizing 2-FDG.

Aldehyde Reductase↗

PubMed1992

Quantitative histochemical changes in enzymes involved in energy metabolism in the rat brain during postnatal development. II. Glucose-6-phosphate dehydrogenase and beta-hydroxybutyrate dehydrogenase.

The postnatal maturation of glucose-6-phosphate and beta-hydroxybutyrate dehydrogenase activity was assessed by histochemistry in rats at eight postnatal stages, P0, P5, P10, P14, P17, P21, P35 and the adult stage. Enzyme activities were revealed on cryostat brain sections with nitroblue tetrazolium. Both enzyme activities were low and homogeneous at birth, and increased to reach a peak in all areas studied, at P17 for beta-hydroxybutyrate dehydrogenase and at P21 for glucose-6-phosphate dehydrogenase. Then, glucose-6-phosphate dehydrogenase activity decreased regularly by 20-49% from P21 to adult stage, except in cerebellar white matter where activity did not change after P21. beta-hydroxybutyrate dehydrogenase activity decreased regularly from P17 to adult stage in globus pallidus, hippocampus, thalamus, brainstem, genu of corpus callosum and cerebellar white matter. It sensorimotor cortex, medial geniculate body, caudate nucleus, hypothalamus and inferior colliculus, beta-hydroxybutyrate dehydrogenase activity stayed stable between P17 and P35 and decreased thereafter to adult levels. Finally, in parietal, auditory and cerebellar cortices, beta-hydroxybutyrate dehydrogenase activity either stayed stable or slightly increased after P17. The present study shows that there is a quite good correlation between postnatal changes in cerebral glucose-6-phosphate and beta-hydroxybutyrate dehydrogenase activities and the importance of pentose phosphate pathway and ketone body utilization in the developing brain. Our results also reflect the regional heterogeneity of beta-hydroxybutyrate utilization in the adult rat brain, translating into a remaining high activity of beta-hydroxybutyrate dehydrogenase in cerebral cortex.

Aging↗

PubMed2006

The effect of glucose on the progression of the nuclear maturation of pig oocytes.

The progression of the nuclear maturation of oocytes is a useful marker for the estimation of the subsequent developmental competence of oocytes. In this study, we examined the effect of energy substrates in an in vitro maturation medium on the progression of the nuclear maturation of oocytes. In experiment 1, the supplementation of the maturation medium with 0, 5 and 10 mM of glucose lead to increase in the total cell number of the blastocysts. In experiments 2 and 3, the maturation phase was divided into two stages (germinal vesicle (GV) stage: 0-20 h and nuclear maturation stage: 20-44 h), and the effects of glucose or pyruvate added at each stage on the kinetics of nuclear maturation were examined. The addition of glucose at the nuclear maturation stage rather than at the GV stage of maturation effected greater acceleration in the progression of nuclear maturation. However, the addition of pyruvate at both stages had the same effect on the progression of nuclear maturation was the same. In addition, when glucose was added to the medium containing pyruvate, an additive effect on the progression of nuclear maturation was observed (experiment 4). In experiment 5, the inhibitors of glucose-6-phosphate dehydrogenase (G6PD), dehydroepiandrosterone (DHEA) and 6-aminonicotinamide (6-AN) decreased the rate of the final maturation of oocytes and reduced the difference between the rates of the final maturation of oocytes cultured with glucose and those cultured with pyruvate. In the experiment 6, when the activator of G6PD, brilliant cresyle blue (BCB), was added to the maturation medium, the progression of nuclear maturation was significantly accelerated. The results of this study suggested that in addition to the role of an energy substrate, glucose or its metabolites play a role in nuclear maturation. This role was more pronounced at the second stage of maturation (transition from GV breakdown (GVBD) to M2), probably due to the metabolism of glucose via the pentose phosphate pathway (PPP) rather than the glycolysis pathway.

6-Aminonicotinamide↗

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