Key Enzymes Of Glucose Metabolism Research Articles

Re-sensitization of 5-FU resistance by SPARC through negative regulation of glucose metabolism in hepatocellular carcinoma

Secreted protein, acidic and rich in cysteine (SPARC), a calcium-binding matricellular glycoprotein, is implicated in the progression of many cancers. Currently, there is growing evidence for important functions of SPARC in a variety of cancers and its role in cancer depends on tumor types. In this study, we reported SPARC negatively regulated glucose metabolism in hepatocellular carcinoma (HCC). Overexpression of SPARC inhibited glucose uptake and lactate product through downregulation of key enzymes of glucose metabolism. On the other hand, knock down of SPARC reversed the phenotypes. Meanwhile, exogenous expression of SPARC in HepG2 cells resulted in tolerance to low glucose and was correlated with AMPK pathway. Interestingly, the 5-fluorouracil (5-FU)-resistant HepG2 cells showed increased glucose metabolism and downregulated SPARC levels. Finally, we reported the overexpression of SPARC re-sensitize 5-FU-resistant cells to 5-FU through inhibition of glycolysis both in vitro and in vivo. Our study proposed a novel function of SPARC in the regulation of glucose metabolism in hepatocellular carcinoma and will facilitate the development of therapeutic strategies for the treatments of liver tumor patients.

Effects of N-adamantyl-4-methylthiazol-2-amine on hyperglycemia, hyperlipidemia and oxidative stress in streptozotocin-induced diabetic rats

Thiazole derivatives are attractive candidates for drug development because they can be efficiently synthesized and are active against a number of diseases and conditions, including diabetes. In our present study, we investigated the anti-inflammatory and antioxidant properties of N-adamantyl-4-methylthiazol-2-amine (KHG26693), a new thiazole derivative, in a streptozotocin (STZ)-induced model of diabetes mellitus. STZ-induced diabetic rats were intraperitoneally administered KHG26693 (3mg/kg-body weight/day) for 4 weeks. KHG26693 administration significantly decreased blood glucose, triglycerides, and cholesterol and increased insulin. KHG26693 also suppressed several inflammatory responses in STZ-induced diabetic rats, as evidenced by decreased levels of serum tumor necrosis factor-α, interleukin-1β, and nitric oxide. Additionally, KHG26693 significantly modulated hepatic lipid peroxidation, catalase and superoxide dismutase activity, and the nonenzymatic antioxidant status (e.g., vitamins C and E), and reduced the glutathione content. These anti-inflammatory/antioxidative actions occurred as a result of the downregulation of inducible nitric oxide synthase and nuclear factor-kappa B. Taken together, our results suggest that KHG26693 successfully reduces the production of oxidative stress in STZ-induced diabetic rats by regulating the oxidation–reduction system, specifically increasing antioxidant capacity. Furthermore, KHG26693 treatment significantly reverted the key enzymes of glucose metabolism, such as glucokinase, glucose-6-phosphatase, glycogen synthase, glycogen phosphorylase, and fructose-1,6-bisphosphatase, to near-normal levels in liver tissues. These results indicate that KHG26693 normalizes disturbed glucose metabolism by enhancing glucose utilization and decreasing liver glucose production via insulin release, suggesting the possibility of future diabetes treatments.

Ameliorating effect of eugenol on hyperglycemia by attenuating the key enzymes of glucose metabolism in streptozotocin-induced diabetic rats

Epidemiological studies have demonstrated that diabetes mellitus is a serious health burden for both governments and healthcare providers. This study was hypothesized to evaluate the antihyperglycemic potential of eugenol by determine the activities of key enzymes of glucose metabolism in streptozotocin (STZ)-induced diabetic rats. Diabetes was induced into male albino Wistar rats by intraperitoneal administration of STZ (40 mg/kg body weight (b.w.)). Eugenol was administered to diabetic rats intragastrically at 2.5, 5, and 10 mg/kg b.w. for 30 days. The dose 10 mg/kg b.w. significantly reduced the levels of blood glucose and glycosylated hemoglobin (HbA1c) and increased plasma insulin level. The altered activities of the key enzymes of carbohydrate metabolism such as hexokinase, pyruvate kinase, glucose-6-phosphate dehydrogenase, glucose-6-phosphatase, fructose-1,6-bisphosphatase, and liver marker enzymes (AST, ALT, and ALP), creatine kinase and blood urea nitrogen in serum and blood of diabetic rats were significantly reverted to near normal levels by the administration of eugenol. Further, eugenol administration to diabetic rats improved body weight and hepatic glycogen content demonstrated the antihyperglycemic potential of eugenol in diabetic rats. The present findings suggest that eugenol can potentially ameliorate key enzymes of glucose metabolism in experimental diabetes, and it is sensible to broaden the scale of use of eugenol in a trial to alleviate the adverse effects of diabetes.

Modulatory effect of green tea extract on hepatic key enzymes of glucose metabolism in streptozotocin and high fat diet induced diabetic rats

The study was undertaken to evaluate the antidiabetic effect of green tea extract on carbohydrate metabolic key enzymes in control and streptozotocin high fat diet -induced diabetic rats. The daily oral treatment of green tea extract (300mg/kg body weight) to diabetic rats for 30 days resulted in a significant reduction in the levels of plasma glucose, glycosylated hemoglobin (HbA1c) and increase in the levels of insulin and hemoglobin. The altered activities of the key enzymes of carbohydrate metabolism such as hexokinase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphatase, fructose-1,6-bisphosphatase, glucose-6-phosphate dehydrogenase, glycogen synthase and glycogen phosphorylase in liver of diabetic rats were significantly reverted to near normal levels by the administration of green tea extract. Further, green tea extract administration to diabetic rats improved muscle and hepatic glycogen content suggesting the antihyperglycemic potential of green tea extract in diabetic rats. The obtained results were compared with metformin, a standard oral hypoglycemic drug. Thus, this study indicates that the administration of green tea extract to diabetic rats resulted in alterations in the metabolism of glucose with subsequent reduction in plasma glucose levels.

Effects of linalool on inflammation, matrix accumulation and podocyte loss in kidney of streptozotocin-induced diabetic rats

Context: This study aimed to evaluate the renoprotective action of linalool (LIN) on streptozotocin (STZ)-induced diabetic rats.Objective: The pathological changes in diabetic nephropathy (DN) include oxidative stress, renal injury, matrix accumulation and podocyte abnormalities. We investigated the renoprotective actions of LIN, a monoterpene alcohol, present in herbal essential oils in STZ-induced diabetic rats with renal injury.Materials and methods: STZ-diabetic rats were administered LIN (25 mg/kg) for 45 days, after which the activities of key enzymes of glucose metabolism, collagen content, oxidative damage and expression of glucose transporter-1 (GLUT-1), transforming growth factor-β1 (TGF-β1), nuclear factor-κBp65 (NF-κB p65) and nephrin were analyzed.Results: Diabetic rats displayed altered glucose metabolism, collagen accumulation and increased TGF-β1 and NF-κB expression in kidney. LIN treatment restored glucose-metabolizing enzymes, collagen content and GLUT-1 expression and also prevented nephrin loss. LIN also rescued kidney from oxidative stress and inflammation by decreasing the expression of TGF-β1 and NF-κB. Ultrastructural changes such as basement membrane thickening, reduction in podocyte number and loss of filtration barrier integrity in diabetic rats were mitigated by LIN.Discussion and conclusion: The results of this study suggest that LIN can attenuate nephropathic changes induced in kidney of diabetic rats. These findings highlight the utility of LIN as a potential drug to treat renal damage in diabetic subjects.

Hypoxia Promotes Glycogen Accumulation through Hypoxia Inducible Factor (HIF)-Mediated Induction of Glycogen Synthase 1

When oxygen becomes limiting, cells reduce mitochondrial respiration and increase ATP production through anaerobic fermentation of glucose. The Hypoxia Inducible Factors (HIFs) play a key role in this metabolic shift by regulating the transcription of key enzymes of glucose metabolism. Here we show that oxygen regulates the expression of the muscle glycogen synthase (GYS1). Hypoxic GYS1 induction requires HIF activity and a Hypoxia Response Element within its promoter. GYS1 gene induction correlated with a significant increase in glycogen synthase activity and glycogen accumulation in cells exposed to hypoxia. Significantly, knockdown of either HIF1α or GYS1 attenuated hypoxia-induced glycogen accumulation, while GYS1 overexpression was sufficient to mimic this effect. Altogether, these results indicate that GYS1 regulation by HIF plays a central role in the hypoxic accumulation of glycogen. Importantly, we found that hypoxia also upregulates the expression of UTP:glucose-1-phosphate urydylyltransferase (UGP2) and 1,4-α glucan branching enzyme (GBE1), two enzymes involved in the biosynthesis of glycogen. Therefore, hypoxia regulates almost all the enzymes involved in glycogen metabolism in a coordinated fashion, leading to its accumulation. Finally, we demonstrated that abrogation of glycogen synthesis, by knock-down of GYS1 expression, impairs hypoxic preconditioning, suggesting a physiological role for the glycogen accumulated during chronic hypoxia. In summary, our results uncover a novel effect of hypoxia on glucose metabolism, further supporting the central importance of metabolic reprogramming in the cellular adaptation to hypoxia.

Anti-diabetic activity of Tinospora cordifolia (Willd.) in streptozotocin diabetic rats; does it act like sulfonylureas?

As an alternative medicine to treat diabetes mellitus, many herbal drugs are being studied throughout the world. In the present study, an attempt was made to investigate the anti-diabetic activity of Tinospora cordifolia (Willd.) (TC) stem extracts (both aqueous and alcoholic) in different dosages (200 and 400 mg/kg b.w.) in streptozotocin diabetic albino rats. The probable mechanism by which TC may act as an anti-hyperglycemic drug was also investigated. Materials and methods: The drug was administered orally for 10 days and 30 days in different groups of animal, with each group containing 6 animals. The efficacy of this drug was compared with the Lante Zinc Insulin (6 U/kg b.w. daily, i.p.) treated diabetic rats. The serum insulin levels, histology of endocrine pancreas and activity of key enzymes of glucose metabolism, i.e. glycogen synthase and glycogen phosphorylase, were studied. Results: Our study clearly showed that TC has significant (P < 0.05) anti-diabetic activity in diabetic animals and has an efficacy of 40% to 80% compared to insulin. TC administration in diabetic animals did not cause any increase in serum insulin levels or regeneration of pancreatic \beta cells but caused increased hepatic glycogen synthase and decreased glycogen phosphorylase activity. Conclusion: The probable mechanism by which TC may act as an anti-hyperglycemic drug is not through insulin secretion like sulfonylureas. It may be through some peripheral mechanisms, such as increasing the glycogen storage in the liver or decreasing the glucose release from the liver.

Efficacy of coumarin on hepatic key enzymes of glucose metabolism in chemical induced type 2 diabetic rats

The study was undertaken to evaluate the antidiabetic effect of coumarin on carbohydrate metabolic key enzymes in control and streptozotocin (STZ)–nicotinamide (NA)-induced diabetic rats. On oral administration of coumarin at a dose of 100 mg/kg body weight per day to diabetic rats for 45 days; resulted in a significant reduction in the levels of plasma glucose, glycosylated hemoglobin (HbA 1c) and increase in the levels of insulin and hemoglobin. Administration of coumarin caused a significant increase in the levels of glycolytic enzyme (hexokinase) and hepatic shunt enzyme (glucose-6-phophate dehydrogenase) whereas significant decrease in the levels of gluconeogenic enzymes (glucose-6-phosphatase and fructose-1,6-bisphosphatase) in diabetic treated rats. Furthermore, protection against body weight loss of diabetic animals also observed. This study indicates that the administration of coumarin to diabetic rats resulted in alterations in the metabolism of glucose with subsequent reduction in plasma glucose levels.

Investigation on the mechanism of dichloroacetate (DCA) induced apoptosis in breast cancer

e14637 Background: DCA is a generic, orally available, small molecule metabolic modulator that has an established history in the treatment of mitochondrial diseases and lactic acidosis. DCA inhibits pyruvate dehydrogenase kinase (PDK), an inhibitor of pyruvate dehydrogenase, a key enzyme in glucose metabolism. DCA preferentially shifts glucose metabolism in cancer cells from glycolysis to glucose oxidation, reversing the unique aerobic glycolysis found in solid tumors. DCA induced apoptosis in cancer cells as evidenced by the efflux of cytochrome c and apoptosis-inducing factor from the mitochondria. Recent studies suggested apoptosis induction by DCA in glioblastoma, endometrial, prostate, and non-small cell lung cancers. In this study we attempt to establish a link between DCA and apoptosis in breast cancer cell lines. Methods: Six breast cancer cell lines were investigated (BT474, MCF-7, MDA-MB231, MDA- MB468, SKBR3, T47D). Quantitative real-time polymerase chain reaction (RT-PCR) was performed using Taqman probes to identify increased DNA templates of PDK isoforms 1–4, using DCA concentrations from 0 to 20mM. Western blots were performed to identify increased expression of PDK isoforms and correlate findings with Taqman. MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)- 2-(4-sulfophenyl)-2H-tetrazolium) assays were performed to measure decreased mitochondrial activity and cytotoxicity. Flow cytometry using annexin V and propidium iodide was performed to measure apoptosis and cell death. Results: RT-PCR showed increased DNA expression of all PDK isoforms in MDA-MB231 cells after DCA treatment. The effect was most pronounced at 10mM concentration. 10mM of DCA also increased DNA expression of all PDK isoforms in MCF-7 cells, and PDK1 in T47D cells. MTS assays showed increased cell kill and decreased mitochondrial activity in all six cell lines, with IC50 ranging between 20mM and 30 mM. Flow cytometry showed increased apoptosis induced by DCA at IC50 for BT474 and MCF-7 cell lines. Conclusions: Apoptosis appears to play a role in the mechanism of DCA in breast cancer, with increased PDK isoform expressions, cytotoxicity and decreased mitochondrial activity. Data from flow cytometry suggested DCA-induced apoptosis in two cell lines. No significant financial relationships to disclose.

Nucleomics: Targeting and Genetic Analysis of Nutrient‐Sensing Cells

Pancreatic β‐cells are the most abundant nutrient sensing cell (NSC) type with fewer seen in the hypothalamus and intestine. It is difficult to study NSC's because they are embedded within other cell types in these organs. We showed that glucokinase (GK), a key enzyme in glucose metabolism in β‐cells, is also expressed in the other NSC's. To study NSC's, we developed a gene construct coding for a nuclear targeted fluorescent protein (FP) with a GK promoter to drive expression. Fluorescent nuclei can be rapidly extracted and purified by cell sorting, and the RNA isolated from these nuclei used to evaluate NSC specific gene expression. MIN6 β‐cells were transfected with this plasmid, and targeting of the FP to nuclei of only GK expressing cells was verified by microscopy. Clonal cell lines expressing the construct are now being expanded. Nuclei were isolated after cell disruption, and differential density centrifugation. All nuclei were labeled with a DNA probe DAPI (blue) and all stained nuclei were sorted by FACS, with NSC specific nuclei purified in the FP window. Results show that NSC nuclei and RNA can be isolated away from other cells, thereby providing a method for NSC specific gene analysis. This study will guide development of a mouse line in which changes in β‐cell (and nutrient sensing cells in general) gene expression can be studied during the onset of obesity and diabetes.

S26948, a new specific peroxisome proliferator activated receptor gamma modulator improved in vivo hepatic insulin sensitivity in 48 h lipid infused rats

We examined whether S26948, a new specific peroxisome proliferator activated receptor γ modulator prevented insulin-resistance induced by a 48 h intralipid-infusion in normal rat (IL rats). The effect of S26948 (30 mg/kg) was compared to rosiglitazone (10 mg/kg). Rats were catheterized in the right jugular vein 4 days before the beginning of the 48 h lipid or saline infusions. Animals were intraperitoneally injected once daily with vehicle, S26948 or rosiglitazone. At the end of the infusion the rats underwent either a glucose tolerance test or a euglycemic–hyperinsulinemic clamp. Finally isolation and incubation of hepatocytes in another series of rats were performed. Intralipid infusion leads to a 4-fold increase in plasma free fatty acid concentration compared to controls (C). Both S26948 and rosiglitazone decreased plasma free fatty acid concentration in IL rats compared to vehicle treated IL rats. Glucose-induced insulin secretion was significantly increased in IL compared to C and was associated with insulin resistance. Both S26948 and rosiglitazone treatments normalized glucose-induced insulin secretion and improved insulin action in IL rats. However, S26948 specifically improved hepatic insulin sensitivity whereas rosiglitazone improved both hepatic insulin sensitivity and insulin-stimulated glucose utilization. Finally, studies on isolated hepatocytes showed differential effect of both compounds on gene expression of key enzymes of glucose metabolism. Our data show that non thiazolidinedione S26948 may represent an alternative way for the management of dysregulated hepatic insulin sensitivity.

Biophysical Characterization of the Interaction between Hepatic Glucokinase and Its Regulatory Protein: IMPACT OF PHYSIOLOGICAL AND PHARMACOLOGICAL EFFECTORS

Glucokinase (GK) is a key enzyme of glucose metabolism in liver and pancreatic beta-cells, and small molecule activators of GK (GKAs) are under evaluation for the treatment of type 2 diabetes. In liver, GK activity is controlled by the GK regulatory protein (GKRP), which forms an inhibitory complex with the enzyme. Here, we performed isothermal titration calorimetry and surface plasmon resonance experiments to characterize GK-GKRP binding and to study the influence that physiological and pharmacological effectors of GK have on the protein-protein interaction. In the presence of fructose-6-phosphate, GK-GKRP complex formation displayed a strong entropic driving force opposed by a large positive enthalpy; a negative change in heat capacity was observed (Kd = 45 nm, DeltaH = 15.6 kcal/mol, TDeltaS = 25.7 kcal/mol, DeltaCp = -354 cal mol(-1) K(-1)). With k(off) = 1.3 x 10(-2) s(-1), the complex dissociated quickly. The thermodynamic profile suggested a largely hydrophobic interaction. In addition, effects of pH and buffer demonstrated the coupled uptake of one proton and indicated an ionic contribution to binding. Glucose decreased the binding affinity between GK and GKRP. This decrease was potentiated by an ATP analogue. Prototypical GKAs of the amino-heteroaryl-amide type bound to GK in a glucose-dependent manner and impaired the association of GK with GKRP. This mechanism might contribute to the antidiabetic effects of GKAs.

Proteomic and Metabolomic Analysis of Smooth Muscle Cells Derived From the Arterial Media and Adventitial Progenitors of Apolipoprotein E–Deficient Mice

We have recently demonstrated that stem cell antigen 1-positive (Sca-1(+)) progenitors exist in the vascular adventitia of apolipoprotein E-deficient (apoE(-/-)) mice and contribute to smooth muscle cell (SMC) accumulation in vein graft atherosclerosis. Using a combined proteomic and metabolomic approach, we now characterize these local progenitors, which participate in the formation of native atherosclerotic lesions in chow-fed apoE(-/-) mice. Unlike Sca-1(+) progenitors from embryonic stem cells, the resident Sca-1(+) stem cell population from the vasculature acquired a mature aortic SMC phenotype after platelet-derived growth factor-BB stimulation. It shared proteomic and metabolomic characteristics of apoE(-/-) SMCs, which were clearly distinct from wild-type SMCs under normoxic and hypoxic conditions. Among the differentially expressed proteins were key enzymes in glucose metabolism, resulting in faster glucose consumption and a compensatory reduction in baseline interleukin-6 secretion. The latter was associated with a marked upregulation of insulin-like growth factor binding proteins (IGFBPs) 3 and 6. Notably, reconstitution of interleukin-6 to levels measured in the conditioned medium of wild-type SMCs attenuated the elevated IGFBP expression in apoE(-/-) SMCs and their vascular progenitors. This coregulation of apoE, interleukin-6, and IGFBPs was replicated in wild-type SMCs from hypercholesterolemic mice and confirmed by silencing apoE expression in SMCs from normocholesterolemic mice. In summary, we provide evidence that Sca-1(+) progenitors contribute to native atherosclerosis in apoE(-/-) mice, that apoE deficiency and hypercholesterolemia alter progenitor cell behavior, and that inflammatory cytokines such as interleukin-6 act as metabolic regulators in SMCs of hyperlipidemic mice.

Nitration of a Critical Tyrosine Residue in the Allosteric Inhibitor Site of Muscle Glycogen Phosphorylase Impairs its Catalytic Activity

Muscle glycogen phosphorylase (GP) is a key enzyme in glucose metabolism, and its impairment can lead to muscle dysfunction. Tyrosine nitration of glycogen phosphorylase occurs during aging and has been suggested to be involved in progressive loss of muscle performance. Here, we show that GP (in its T and R form) is irreversibly impaired by exposure to peroxynitrite, a biological nitrogen species known to nitrate reactive tyrosine residues, and to be involved in physiological and pathological processes. Kinetic and biochemical analysis indicated that irreversible inactivation of GP by peroxynitrite is due to the fast (kinact=3×104 M−1 s−1) nitration of a unique tyrosine residue of the enzyme. Endogenous GP was tyrosine nitrated and irreversibly inactivated in skeletal muscle cells upon exposure to peroxynitrite, with concomitant impairment of glycogen mobilization. Ligand protection assays and mass spectrometry analysis using purified GP suggested that the peroxynitrite-dependent inactivation of the enzyme could be due to the nitration of Tyr613, a key amino acid of the allosteric inhibitor site of the enzyme. Our findings suggest that GP functions may be regulated by tyrosine nitration.

ASSESMENT OF BIOACTIVITY OF A FISCHERELLA SPECIES COLONIZING AZADIRACHTA INDICA (NEEM) BARK

In order to investigate whether a. Fischerella sp. colonizing Azadirachta indica (neem) bark is able to show, like neem derived extracts/products, bioactivity with respect to glucose metabolizing potential in animal models, laboratory cultivated neem colonized cyanobacterial biomass was fed to mice and its effects on liver lactate dehydrogenase (LDH: a key enzyme of glucose metabolism) vis a vis blood glucose level was monitored. Neem bark extract and purified azadirachtin (a bioactive neem product) were also tested simultaneously for comparison. As compared to the control, none of the samples could produce much variation in blood glucose levels except a transitory decline, 34% and 26% at 2 nd & 12 th h, in azadirachtin and Fischerella (isolated from neem) fed mice respectively. However, all the test samples showed significant increase in liver LDH activity after 2nd h of treatment (p< 0.01) followed by a decline at 6th h. Thereafter, the enzyme activity increased progressively up to 24 th h in mice fed with azadirachtin and neem colonized Fischerella only (p < 0.001 at 24 th h). Expression pattern of the enzyme was also studied using polyacrylamide gel electrophoresis. Liver specific M4-LDH (homo-tetramer of M sub-unit) was detected in all the cases and time-dependent changes in expression of the enzyme paralleled the alterations observed in its activities. To ascertain whether such a bioactivity is common with Fischerella sp. colonizing other trees also, liver LDH profile was compared between mice fed with Fischerella isolated from neem and jamun (Eugenia jambolana) barks separately. Though Fischerella from jamun did not alter liver LDH profile, Fischerella isolated from neem could produce significant increase in the enzyme activity (p < 0.001) and corresponding changes in the expression of LDH isozymes. The results suggest that Fischerella sp. inhabiting neem bark, like bioactivity of its host plant products, modulates activity and expression of liver LDH in mice.

Effect of pterostilbene on hepatic key enzymes of glucose metabolism in streptozotocin- and nicotinamide-induced diabetic rats

The purpose of this study was to investigate the effect of pterostilbene and its effect on key enzymes of glucose metabolism. Diabetic rats were orally administered with pterostilbene (10, 20, 40 mg/kg) for 2, 4 and 6 weeks on glucose was determined. Administration of pterostilbene at 40 mg/kg significantly decreases plasma glucose. Based on these data, the higher dose, 40 mg/kg pterostilbene, was selected for further evaluation. Oral administration of pterostilbene for 6 weeks on glucose, insulin levels and hepatic enzymes in normal and streptozotocin (STZ)–nicotinamide-induced diabetic rats. A significant decrease in glucose and significant increase in plasma insulin levels were observed in normal and diabetic rats treated with pterostilbene. Treatment with pterostilbene resulted in a significant reduction of glycosylated hemoglobin and an increase in total hemoglobin level. The activities of the hepatic enzymes such as hexokinase was significantly increased whereas glucose-6-phosphatase, fructose-1,6-bisphosphatase were significantly decreased by the administration of pterostilbene in diabetic rats. A comparison was made between the action of pterostilbene and the antidiabetic drug – metformin.

Inhibition of phosphoglucomutase activity by lithium alters cellular calcium homeostasis and signaling in Saccharomyces cerevisiae

Phosphoglucomutase is a key enzyme of glucose metabolism that interconverts glucose-1-phosphate and glucose-6-phosphate. Loss of the major isoform of phosphoglucomutase in Saccharomyces cerevisiae results in a significant increase in the cellular glucose-1-phosphate-to-glucose-6-phosphate ratio when cells are grown in medium containing galactose as carbon source. This imbalance in glucose metabolites was recently shown to also cause a six- to ninefold increase in cellular Ca2+ accumulation. We found that Li+ inhibition of phosphoglucomutase causes a similar elevation of total cellular Ca2+ and an increase in 45Ca2+ uptake in a wild-type yeast strain grown in medium containing galactose, but not glucose, as sole carbon source. Li+ treatment also reduced the transient elevation of cytosolic Ca2+ response that is triggered by exposure to external CaCl2 or by the addition of galactose to yeast cells starved of a carbon source. Finally, we found that the Ca2+ over-accumulation induced by Li+ exposure was significantly reduced in a strain lacking the vacuolar Ca2+-ATPase Pmc1p. These observations suggest that Li+ inhibition of phosphoglucomutase results in an increased glucose-1-phosphate-to-glucose-6-phosphate ratio, which results in an accelerated rate of vacuolar Ca2+ uptake via the Ca2+-ATPase Pmc1p.

Hepatic glucokinase turnover in intact and adrenalectomized rats in vivo.

Regulation of synthesis and degradation of glucokinase, key enzyme of glucose metabolism in liver, was investigated in intact and adrenalectomized rats in vivo, using pulse-labeling experiments and a specific antibody against the enzyme. Refeeding glucose in starved rats resulted in a marked rise in glucokinase activity (from the starvation value 4.8 mU/mg protein to 9.6 mU/mg protein at 4 h, and to 21.8 mU/mg protein at 8 h), which closely correlated to the increase in enzyme synthesis by factor 1.7 at 4 h and 4.1 at 8 h. Similar alterations in enzyme activity and synthesis were observed after glucose refeeding in adrenalectomized/glucocorticoid-restored rats. In contrast, refeeding glucose in adrenalectomized rats led within 8 h only to a small elevation in enzyme activity (from the starvation value 4.2 mU/mg protein to 9.6 mU/mg protein) and a minor rise in enzyme synthesis (factor 1.7). Glucocorticoids per se were without effect on glucokinase activity and synthesis in starved rats. When adapted to pure glucose diet, intact, adrenalectomized and adrenalectomized/glucocorticoid-restored rats showed highly elevated levels in glucokinase (27, 23, 28 mU/mg protein, respectively). However, enzyme synthesis was elevated significantly only in intact and adrenalectomized/glucocorticoid-restored rats. Under these conditions glucokinase degradation was estimated by the double-pulse-labeling technique, applying [14C]leucine and [3H]leucine. From the 3H/14C ratios the apparent half-lives were calculated: 17 h in intact and adrenalectomized/glucocorticoid-restored rats, and 35 h in adrenalectomized rats. It is concluded that in vivo glucocorticoids not only exert a 'permissive' action on glucokinase induction, but also enhance the degradation of the enzyme.

Postnatal maturation of cytochrome oxidase and lactate dehydrogenase activity and age-dependent consequences of lithium-pilocarpine status epilepticus in the rat: a regional histoenzymology study.

The lithium-pilocarpine (Li-Pilo) model of epilepsy reproduces some pathophysiological, temporal, and developmental features of human temporal lobe epilepsy. In this model, rates of cerebral glucose utilization measured by the [(14)C]2-deoxyglucose technique increased during the initial status epilepticus (SE) and decreased during the latent or chronic periods. To correlate these metabolic changes with the activities of the enzymes of the glycolytic and tricarboxylic acid cycle pathways, we measured by histoenzymology the regional activity of two key enzymes of glucose metabolism, lactate dehydrogenase (LDH) for the anaerobic pathway and cytochrome oxidase (CO) for the aerobic pathway coupled to oxidative phosphorylation, at various times after SE induced by Li-Pilo in 10- (P10), 21-d-old (P21) and adult rats for CO and in adult rats only for LDH. CO activity was slightly affected in P10 and P21 rats only at 4 and 24 h and normalized by 14 d after SE. In adult rats, CO activity decreased at 4 and 24 h in damaged areas, like entorhinal cortex, hippocampal CA3 area, amygdala, and thalamus. At 14 d after SE, CO activity was decreased only in entorhinal cortex and increased in brainstem regions involved in the remote control of seizures. In adult rats, LDH activity decreased at 24 h and 14 d after SE in sensorimotor and entorhinal cortex. These data show that the enzymatic equipment underlying the metabolism of glucose is not severely affected by Li-Pilo SE and confirm our previous observations concerning the relative metabolic hyperactivity of brain regions involved in the seizure circuit despite marked neuronal loss.

Basal levels of metabolic activity are elevated in Genetic Absence Epilepsy Rats from Strasbourg (GAERS): measurement of regional activity of cytochrome oxidase and lactate dehydrogenase by histochemistry

The Genetic Absence Epilepsy Rats from Strasbourg (GAERS) are considered an isomorphic, predictive, and homologous model of human generalized absence epilepsy. It is characterized by the expression of spike-and-wave discharges in the thalamus and cortex. In this strain, basal regional rates of cerebral glucose utilization measured by the quantitative autoradiographic [ 14C]2-deoxyglucose technique display a widespread consistent increase compared to a selected strain of genetically nonepileptic rats (NE). In order to verify whether these high rates of glucose metabolism are paralleled by elevated activities of the enzymes of the glycolytic and tricarboxylic acid cycle pathways, we measured by histochemistry the regional activity of the two key enzymes of glucose metabolism, lactate dehydrogenase (LDH) for the anaerobic pathway and cytochrome oxidase (CO) for the aerobic pathway coupled to oxidative phosphorylation. CO and LDH activities were significantly higher in GAERS than in NE rats in 24 and 28 of the 30 brain regions studied, respectively. The differences in CO and LDH activity between both strains were widespread, affected all brain systems studied, and ranged from 12 to 63%. The data of the present study confirm the generalized increase in cerebral glucose metabolism in GAERS, occurring both at the glycolytic and at the oxidative step. However, they still do not allow us to understand why the ubiquitous mutation(s) generates spike-and-wave discharges only in the thalamocortical circuit.