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Anthracyclines' cardiotoxicity involves an accelerated generation of reactive oxygen species. This oxidative damage has been found to accelerate the expression of hexose-6P-dehydrogenase (H6PD), that channels glucose-6-phosphate (G6P) through the pentose phosphate pathway (PPP) confined within the endoplasmic/sarcoplasmic reticulum (SR). To verify the role of SR-PPP in the defense mechanisms activated by doxorubicin (DXR) in cardiomyocytes, we tested the effect of this drug in H6PD knockout mice (H6PD−/−). Twenty-eight wildtype (WT) and 32 H6PD−/− mice were divided into four groups to be treated with intraperitoneal administration of saline (untreated) or DXR (8 mg/Kg once a week for 3 weeks). One week thereafter, survivors underwent imaging of 18F-deoxyglucose (FDG) uptake and were sacrificed to evaluate the levels of H6PD, glucose-6P-dehydrogenase (G6PD), G6P transporter (G6PT), and malondialdehyde. The mRNA levels of SR Ca2+-ATPase 2 (Serca2) and ryanodine receptors 2 (RyR2) were evaluated and complemented with Hematoxylin/Eosin staining and transmission electron microscopy. During the treatment period, 1/14 DXR-WT and 12/18 DXR-H6PD−/− died. At microPET, DXR-H6PD−/− survivors displayed an increase in left ventricular size (p < 0.001) coupled with a decreased urinary output, suggesting a severe hemodynamic impairment. At ex vivo analysis, H6PD−/− condition was associated with an oxidative damage independent of treatment type. DXR increased H6PD expression only in WT mice, while G6PT abundance increased in both groups, mismatching a generalized decrease of G6PD levels. Switching-off SR-PPP impaired reticular accumulation of Ca2+ decelerating Serca2 expression and upregulating RyR2 mRNA level. It thus altered mitochondrial ultrastructure eventually resulting in a cardiomyocyte loss. The recognized vulnerability of SR to the anthracycline oxidative damage is counterbalanced by an acceleration of G6P flux through a PPP confined within the reticular lumen. The interplay of SR-PPP with the intracellular Ca2+ exchanges regulators in cardiomyocytes configure the reticular PPP as a potential new target for strategies aimed to decrease anthracycline toxicity. [ABSTRACT FROM AUTHOR]

PARP‐1 over‐activation results in cell death via excessive PAR generation in different cell types, including neurons following brain ischemia. Glycolysis, mitochondrial function, and redox balance are key cellular processes altered in brain ischemia. Studies show that PAR generated after PARP‐1 over‐activation can bind hexokinase‐1 (HK‐1) and result in glycolytic defects and subsequent mitochondrial dysfunction. HK‐1 is the neuronal hexokinase and catalyzes the first reaction of glycolysis, converting glucose to glucose‐6‐phosphate (G6P), a common substrate for glycolysis, and the pentose phosphate pathway (PPP). PPP is critical in maintaining NADPH and GSH levels via G6P dehydrogenase activity. Therefore, defects in HK‐1 will not only decrease cellular bioenergetics but will also cause redox imbalance due to the depletion of GSH. In brain ischemia, whether PAR‐mediated inhibition of HK‐1 results in bioenergetics defects and redox imbalance is not known. We used oxygen–glucose deprivation (OGD) in mouse cortical neurons to mimic brain ischemia in neuronal cultures and observed that PARP‐1 activation via PAR formation alters glycolysis, mitochondrial function, and redox homeostasis in neurons. We used pharmacological inhibition of PARP‐1 and adenoviral‐mediated overexpression of wild‐type HK‐1 (wtHK‐1) and PAR‐binding mutant HK‐1 (pbmHK‐1). Our data show that PAR inhibition or overexpression of HK‐1 significantly improves glycolysis, mitochondrial function, redox homeostasis, and cell survival in mouse cortical neurons exposed to OGD. These results suggest that PAR binding and inhibition of HK‐1 during OGD drive bioenergetic defects in neurons due to inhibition of glycolysis and impairment of mitochondrial function. [ABSTRACT FROM AUTHOR]

Electron cycler-mediated extracellular reduction of the water-soluble tetrazolium salt 1 (WST1) is frequently used as tool for the determination of cell viability. We have adapted this method to monitor by determining the extracellular WST1 formazan accumulation the cellular redox metabolism of cultured primary astrocytes via the NAD(P)H-dependent reduction of the electron cycler β-lapachone by cytosolic NAD(P)H:quinone oxidoreductase 1 (NQO1). Cultured astrocytes that had been exposed to β-lapachone in concentrations of up to 3 µM remained viable and showed an almost linear extracellular accumulation of WST1 formazan for the first 60 min, while higher concentrations of β-lapachone caused oxidative stress and impaired cell metabolism. β-lapachone-mediated WST1 reduction was inhibited by the NQO1 inhibitors ES936 and dicoumarol in a concentration-dependent manner, with half-maximal inhibition observed at inhibitor concentrations of about 0.3 µM. β-lapachone-mediated WST1 reduction depended strongly on glucose availability, while mitochondrial substrates such as lactate, pyruvate or ketone bodies allowed only residual β-lapachone-mediated WST1 reduction. Accordingly, the mitochondrial respiratory chain inhibitors antimycin A and rotenone hardly affected astrocytic WST1 reduction. Both NADH and NADPH are known to supply electrons for reactions catalysed by cytosolic NQO1. Around 60% of the glucose-dependent β-lapachone-mediated WST1 reduction was prevented by the presence of the glucose-6-phosphate dehydrogenase inhibitor G6PDi-1, while the glyceraldehyde-3-phosphate dehydrogenase inhibitor iodoacetate had only little inhibitory potential. These data suggest that pentose phosphate pathway-generated NADPH, and not glycolysis-derived NADH, is the preferred electron source for cytosolic NQO1-catalysed reductions in cultured astrocytes. [ABSTRACT FROM AUTHOR]

To adapt to the tumor environment or to escape chemotherapy, cancer cells rapidly reprogram their metabolism. The hallmark biochemical phenotype of cancer cells is the shift in metabolic reprogramming towards aerobic glycolysis. It was thought that this metabolic shift to glycolysis alone was sufficient for cancer cells to meet their heightened energy and metabolic demands for proliferation and survival. Recent studies, however, show that cancer cells rely on glutamine, lipid, and mitochondrial metabolism for energy. Oncogenes and scavenging pathways control many of these metabolic changes, and several metabolic and tumorigenic pathways are post-transcriptionally regulated by microRNA (miRNAs). Genes that are directly or indirectly responsible for energy production in cells are either negatively or positively regulated by miRNAs. Therefore, some miRNAs play an oncogenic role by regulating the metabolic shift that occurs in cancer cells. Additionally, miRNAs can regulate mitochondrial calcium stores and energy metabolism, thus promoting cancer cell survival, cell growth, and metastasis. In the electron transport chain (ETC), miRNAs enhance the activity of apoptosis-inducing factor (AIF) and cytochrome c, and these apoptosome proteins are directed towards the ETC rather than to the apoptotic pathway. This review will highlight how miRNAs regulate the enzymes, signaling pathways, and transcription factors of cancer cell metabolism and mitochondrial calcium import/export pathways. The review will also focus on the metabolic reprogramming of cancer cells to promote survival, proliferation, growth, and metastasis with an emphasis on the therapeutic potential of miRNAs for cancer treatment. [ABSTRACT FROM AUTHOR]

Proteins destined for transport to specific organelles usually contain targeting information, which are embedded in their sequence. Many enzymes are required in more than one cellular compartment and different molecular mechanisms are used to achieve dual localization. Here we report a cryptic type 2 peroxisomal targeting signal encoded in the 5′ untranslated region of fungal genes coding for 6-phosphogluconate dehydrogenase (PGD), a key enzyme of the oxidative pentose phosphate pathway. The conservation of the cryptic PTS2 motif suggests a biological function. We observed that translation from a non-AUG start codon generates an N-terminally extended peroxisomal isoform of Ustilago maydis PGD. Non-canonical initiation occurred at the sequence AGG AUU, consisting of two near-cognate start codons in tandem. Taken together, our data reveal non-AUG translation initiation as an additional mechanism to achieve the dual localization of a protein required both in the cytosol and the peroxisomes.

Astrocytes (also, astroglia) consume huge amounts of glucose and produce lactate regardless of sufficient oxygen availability, indicating a high capacity for aerobic glycolysis. Glycolysis in astrocytes is activated in accordance with neuronal excitation and leads to increases in the release of lactate from astrocytes. Although the fate of this lactate remains somewhat controversial, it is believed to fuel neurons as an energy substrate. Besides providing lactate, astrocytic glycolysis plays an important role in neuroprotection. Among the minor pathways of glucose metabolism, glucose flux to the pentose-phosphate pathway (PPP), a major shunt pathway of glycolysis, is attracting research interest. In fact, PPP activity in astrocytes is five to seven times higher than that in neurons. The astrocytic PPP plays a key role in protecting neurons against oxidative stress by providing neurons with a reduced form of glutathione, which is necessary to eliminate reactive oxygen species. Therefore, enhancing astrocytic glycolysis might promote neuronal protection during acute ischemic stroke. Contrariwise, the dysfunction of astrocytic glycolysis and the PPP have been implicated in the pathogenesis of various neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease, and amyotrophic lateral sclerosis, since mitochondrial dysfunction and oxidative stress trigger and accelerate disease progression.

Abstract Background Biologically, hydrogen (H2) can be produced through dark fermentation and photofermentation. Dark fermentation is fast in rate and simple in reactor design, but H2 production yield is unsatisfactorily low as

Anaphase-promoting complex (APC) with its coactivator Cdh1 is required to maintain the postmitotic state of neurons via degradation of Cyclin B1, which aims to prevent aberrant cell cycle entry that causes neuronal apoptosis. Interestingly, evidence is accumulating that apart from the cell cycle, APC-Cdh1 also involves in neuronal metabolism via modulating the glycolysis promoting enzyme, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3). Here, we showed that under oxygen-glucose deprivation and reperfusion (OGD/R), APC-Cdh1 was decreased in primary cortical neurons. Likewise, the neurons exhibited enhanced glycolysis when oxygen supply was reestablished during reperfusion, which was termed as the "neuronal Warburg effect." In particular, the reperfused neurons showed elevated PFKFB3 expression in addition to a reduction in glucose 6-phosphate dehydrogenase (G6PD). Such changes directed neuronal glucose metabolism from pentose-phosphate pathway (PPP) to aerobic glycolysis compared to the normal neurons, resulting in increased ROS production and apoptosis during reperfusion. Pretreatment of neurons with Cdh1 expressing lentivirus before OGD could reverse this metabolic shift and attenuated ROS-induced apoptosis. However, the metabolism regulation and neuroprotection by Cdh1 under OGD/R condition could be blocked when co-transfecting neurons with Ken box-mut-PFKFB3 (which is APC-Cdh1 insensitive). Based on these data, we suggest that the Warburg effect may contribute to apoptotic mechanisms in neurons under OGD/R insult, and targeting Cdh1 may be a potential therapeutic strategy as both glucose metabolic regulator and apoptosis suppressor of neurons in brain injuries. [ABSTRACT FROM AUTHOR]

Ribose-5-phosphate isomerase deficiency, a disorder of the pentose phosphate shunt, was described in 1999. There are 2 previously reported cases of ribose-5-phosphate isomerase deficiency. Here, we describe the clinical course, diagnostic odyssey, and molecular findings in the third case of ribose-5-phosphate isomerase deficiency to further delineate the syndrome. Whole-exome sequencing demonstrated 2 mutations in the ribose-5-phosphate isomerase gene, RPIA, in a child with neonatal onset leukoencephalopathy and psychomotor delays. Urine polyols were elevated confirming deficiency of ribose-5-phosphate isomerase (RPI, EC. 5.3.1.6) and pathogenicity of the variants. Measurement of urine polyols should be considered in cases of early-onset white-matter disease. [ABSTRACT FROM AUTHOR]

Metabolomic markers associated with incident central adiposity gain were investigated in young adults. In a 9-mo prospective study of university freshmen (n = 264). Blood samples and anthropometry measurements were collected in the first 3 d on campus and at the end of the year. Plasma from individuals was pooled by phenotype [incident central adiposity, stable adiposity, baseline hemoglobin A1c (HbA1c) > 5.05%, HbA1c < 4.92%] and assayed using GC-MS, chromatograms were analyzed using MetaboliteDetector software, and normalized metabolite levels were compared using Welch's t test. Assays were repeated using freshly prepared pools, and statistically significant metabolites were quantified in a targeted GC-MS approach. Isotope tracer studies were performed to determine if the potential marker was an endogenous human metabolite in men and in whole blood. Participants with incident central adiposity gain had statistically significantly higher blood erythritol [P < 0.001, false discovery rate (FDR) = 0.0435], and the targeted assay revealed 15-fold [95% confidence interval (CI): 13.27, 16.25] higher blood erythritol compared with participants with stable adiposity. Participants with baseline HbA1c > 5.05% had 21-fold (95% CI: 19.84, 21.41) higher blood erythritol compared with participants with lower HbA1c (P < 0.001, FDR = 0.00016). Erythritol was shown to be synthesized endogenously from glucose via the pentose-phosphate pathway (PPP) in stable isotope-assisted ex vivo blood incubation experiments and through in vivo conversion of erythritol to erythronate in stable isotope-assisted dried blood spot experiments. Therefore, endogenous production of erythritol from glucose may contribute to the association between erythritol and obesity observed in young adults. [ABSTRACT FROM AUTHOR]

Parkinson disease (PD) is a neurodegenerative disorder characterized by a selective loss of dopaminergic neurons in the substantia nigra . The earliest biochemical signs of the disease involve failure in mitochondrial-endoplasmic reticulum cross talk and lysosomal function, mitochondrial electron chain impairment, mitochondrial dynamics alterations, and calcium and iron homeostasis abnormalities. These changes are associated with increased mitochondrial reactive oxygen species (mROS) and energy deficiency. Recently, it has been reported that, as an attempt to compensate for the mitochondrial dysfunction, neurons invoke glycolysis as a low-efficient mode of energy production in models of PD. Here, we review how mitochondria orchestrate the maintenance of cellular energetic status in PD, with special focus on the switch from oxidative phosphorylation to glycolysis, as well as the implication of endoplasmic reticulum and lysosomes in the control of bioenergetics. [ABSTRACT FROM AUTHOR]

Background: Fermentative hydrogen (H2) production suffers from low carbon-to-H2 yield, to which problem, coproduction of ethanol and H2 has been proposed as a solution. For improved co-production of H2 and ethanol, we developed Escherichia coli BW25113 ΔhycA ΔhyaAB ΔhybBC ΔldhA ΔfrdAB Δpta-ackA ΔpfkA (SH8*) and overexpressed Zwf and Gnd, the key enzymes in the pentose-phosphate (PP) pathway (SH8*_ZG). However, the amount of accumulated pyruvate, which was significant (typically 0.20 mol mol-1 glucose), reduced the co-production yield. Results: In this study, as a means of reducing pyruvate accumulation and improving co-production of H2 and ethanol, we developed and studied E. coli SH9*_ZG with functional acetate production pathway for conversion of acetyl-CoA to acetate (pta-ackA+). Our results indicated that the presence of the acetate pathway completely eliminated pyruvate accumulation and substantially improved the co-production of H2 and ethanol, enabling yields of 1.88 and 1.40 mol, respectively, from 1 mol glucose. These yields, significantly, are close to the theoretical maximums of 1.67 mol H2 and 1.67 mol ethanol. To better understand the glycolytic flux distribution, glycolytic flux prediction and RT-PCR analyses were performed. Conclusion: The presence of the acetate pathway along with activation of the PP pathway eliminated pyruvate accumulation, thereby significantly improving co-production of H2 and ethanol. Our strategy is applicable to anaerobic production of biofuels and biochemicals, both of which processes demand high NAD(P)H. [ABSTRACT FROM AUTHOR]

The article presents a study that determines the contribution of pentose-phosphate pathway (PPP) to neuronal glucose consumption. It describes the method of the study which catalyses of glucose-6- phosphate (G6P) by glucose-6-c(G6PD) and 6-phosphogluconate dehydrogenase (6PGD). It discusses the findings of the study which indicates the uncertainties of the role of PPP on neuronal survival.

Vitamin C is an essential factor for neuronal function and survival, existing in two redox states, ascorbic acid ( AA), and its oxidized form, dehydroascorbic acid ( DHA). Here, we show uptake of both AA and DHA by primary cultures of rat brain cortical neurons. Moreover, we show that most intracellular AA was rapidly oxidized to DHA. Intracellular DHA induced a rapid and dramatic decrease in reduced glutathione that was immediately followed by a spontaneous recovery. This transient decrease in glutathione oxidation was preceded by an increase in the rate of glucose oxidation through the pentose phosphate pathway ( PPP), and a concomitant decrease in glucose oxidation through glycolysis. DHA stimulated the activity of glucose-6-phosphate dehydrogenase, the rate-limiting enzyme of the PPP. Furthermore, we found that DHA stimulated the rate of lactate uptake by neurons in a time- and dose-dependent manner. Thus, DHA is a novel modulator of neuronal energy metabolism by facilitating the utilization of glucose through the PPP for antioxidant purposes. [ABSTRACT FROM AUTHOR]

Abstract: Unlike most other cell types, neurons preferentially metabolize glucose via the pentose phosphate pathway (PPP) to maintain their antioxidant status. Inhibiting the PPP in neuronal cell models causes cell death. In rodents, inhibition of this pathway causes selective dopaminergic cell death leading to motor deficits resembling parkinsonism. Using postmortem human brain tissue, we characterized glucose metabolism via the PPP in sporadic Parkinson's disease (PD), Alzheimer's disease (AD), and controls. AD brains showed increased nicotinamide adenine dinucleotide phosphate (NADPH) production in areas affected by disease. In PD however, increased NADPH production was only seen in the affected areas of late-stage cases. Quantifying PPP NADPH-producing enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase by enzyme-linked immunosorbent assay, showed a reduction in the putamen of early-stage PD and interestingly in the cerebellum of early and late-stage PD. Importantly, there was no decrease in enzyme levels in the cortex, putamen, or cerebellum of AD. Our results suggest that down-regulation of PPP enzymes and a failure to increase antioxidant reserve is an early event in the pathogenesis of sporadic PD. [Copyright &y& Elsevier]

Abstract: Red blood cells (RBCs) contain large amounts of iron and operate in highly oxygenated tissues. As a result, these cells encounter a continuous oxidative stress. Protective mechanisms against oxidation include prevention of formation of reactive oxygen species (ROS), scavenging of various forms of ROS, and repair of oxidized cellular contents. In general, a partial defect in any of these systems can harm RBCs and promote senescence, but is without chronic hemolytic complaints. In this review we summarize the often rare inborn defects that interfere with the various protective mechanisms present in RBCs. NADPH is the main source of reduction equivalents in RBCs, used by most of the protective systems. When NADPH becomes limiting, red cells are prone to being damaged. In many of the severe RBC enzyme deficiencies, a lack of protective enzyme activity is frustrating erythropoiesis or is not restricted to RBCs. Common hereditary RBC disorders, such as thalassemia, sickle-cell trait, and unstable hemoglobins, give rise to increased oxidative stress caused by free heme and iron generated from hemoglobin. The beneficial effect of thalassemia minor, sickle-cell trait, and glucose-6-phosphate dehydrogenase deficiency on survival of malaria infection may well be due to the shared feature of enhanced oxidative stress. This may inhibit parasite growth, enhance uptake of infected RBCs by spleen macrophages, and/or cause less cytoadherence of the infected cells to capillary endothelium. [Copyright &y& Elsevier]

Abstract: Recent advances in the field of brain energy metabolism strongly suggest that glutamate receptor-mediated neurotransmission is coupled with molecular signals that switch-on glucose utilization pathways to meet the high energetic requirements of neurons. Failure to adequately coordinate energy supply for neurotransmission ultimately results in a positive amplifying loop of receptor over-activation leading to neuronal death, a process known as excitotoxicity. In this review, we revisited current concepts in excitotoxic mechanisms, their involvement in energy substrate utilization, and the signaling pathways that coordinate both processes. In particular, we have focused on the novel role played by the E3 ubiquitin ligase, anaphase-promoting complex/cyclosome (APC/C)-Cdh1, in cell metabolism. Our laboratory identified 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3) –a key glycolytic-promoting enzyme– as an APC/C-Cdh1 substrate. Interestingly, APC/C-Cdh1 activity is inhibited by over-activation of glutamate receptors through a Ca2+-mediated mechanism. Furthermore, by inhibiting APC/C-Cdh1 activity, glutamate-receptors activation promotes PFKFB3 stabilization, leading to increased glycolysis and decreased pentose-phosphate pathway activity. This causes a loss in neuronal ability to regenerate glutathione, triggering oxidative stress and delayed excitotoxicity. Further investigation is critical to identify novel molecules responsible for the coupling of energy metabolism with glutamatergic neurotransmission and excitotoxicity, as well as to help developing new therapeutic strategies against neurodegeneration. [Copyright &y& Elsevier]

Yeast has been established as an efficient model system to study biological principles underpinning human health. In this review we focus on yeast models covering two aspects of cancer formation and progression (i) the activity of pyruvate kinase (PK), which recapitulates metabolic features of cancer cells, including the Warburg effect, and (ii) chromosome bridge-induced translocation (BIT) mimiking genome instability in cancer. Saccharomyces cerevisiae is an excellent model to study cancer cell metabolism, as exponentially growing yeast cells exhibit many metabolic similarities with rapidly proliferating cancer cells. The metabolic reconfiguration includes an increase in glucose uptake and fermentation, at the expense of respiration and oxidative phosphorylation (the Warburg effect), and involves a broad reconfiguration of nucleotide and amino acid metabolism. Both in yeast and humans, the regulation of this process seems to have a central player, PK, which is up-regulated in cancer, and to occur mostly on a post-transcriptional and posttranslational basis. Furthermore, BIT allows to generate selectable translocation-derived recombinants ("translocants"), between any two desired chromosomal locations, in wild-type yeast strains transformed with a linear DNA cassette carrying a selectable marker flanked by two DNA sequences homologous to different chromosomes. Using the BIT system, targeted non-reciprocal translocations in mitosis are easily inducible. An extensive collection of different yeast translocants exhibiting genome instability and aberrant phenotypes similar to cancer cells has been produced and subjected to analysis. In this review, we hence provide an overview upon two yeast cancer models, and extrapolate general principles for mimicking human disease mechanisms in yeast. [ABSTRACT FROM AUTHOR]

This study aims to investigate the expression and significance of glucose-6-phosphate dehydrogenase (G6PD) in human gastric cancer progression and prognosis. Using immunohistochemistry and real-time RT-PCR assay, we identified abnormally elevated expression of G6PD in gastric cancer tissues compared to paired normal stomach mucosa tissues in 24 patients ( p < 0.05). In order to investigate the correlations between G6PD and the clinicopathological features of gastric cancer, the expression of G6PD in 167 patients with gastric cancer were detected by immunohistochemistry, and the results showed that overexpression of G6PD was associated with the size of tumor ( p = 0.039), depth of invasion ( p = 0.039), lymph node metastasis ( p = 0.044), distant metastasis ( p = 0.003), TNM stage ( p = 0.030), and survival rate ( p = 0.010). Further, Cox multivariates analysis indicated that G6PD expression level was an independent prognostic factor for patients after radical resection ( p = 0.013). In conclusion, overexpression of G6PD is closely related to progression of gastric cancer, and might be regarded as an independent predictor of poor prognosis for gastric cancer. [ABSTRACT FROM AUTHOR]

Thiamine deficiency (TD) impairs hippocampal neurogenesis. However, the mechanisms involved are not identified. In this work, TD mouse model was generated using a thiamine-depleted diet at two time points, TD9 and TD14 for 9 and 14 days of TD respectively. The activities of pyruvate dehydrogenase (PDH), α-ketoglutamate dehydrogenase (KGDH), glucose-6-phosphate dehydrogenase (G6PD), and transketolase (TK), as well as on the contents of NADP+ and NADPH were determined in whole mouse brain, isolated cortex, and hippocampus of TD mice model. The effects of TK silencing on the growth and migratory ability of cultured hippocampal progenitor cells (HPC), as well as on neuritogenesis of hippocampal neurons were explored. The results showed that TD specifically reduced TK activity in both cortex and hippocampus, without significantly affecting the activities of PDH, KGDH, and G6PD in TD9 and TD14 groups. The level of whole brain and hippocampal NADPH in TD14 group were significantly lower than that of control group. TK silencing significantly inhibited the proliferation, growth, and migratory abilities of cultured HPC, without affecting neuritogenesis of cultured hippocampal neurons. Taken together, these results demonstrate that decreased TK activity leads to pentose-phosphate pathway dysfunction and contributes to impaired hippocampal neurogenesis induced by TD. TK and pentose-phosphate pathway may be considered new targets to investigate hippocampal neurogenesis. [ABSTRACT FROM AUTHOR]

Abstract: Our aim was to identify the product formed by sedoheptulokinase and to understand the mechanism of formation of erythritol in patients with sedoheptulokinase deficiency. Mouse recombinant sedoheptulokinase was found to be virtually specific for sedoheptulose and its reaction product was identified as sedoheptulose 7-phosphate. Assays of sedoheptulose in plant extracts disclosed that this sugar is present in carrots (≈7μmol/g) and in several fruits. Sedoheptulose 1-phosphate is shown to be a substrate for aldolase B, which cleaves it to dihydroxyacetone-phosphate and erythrose. This suggests that, in patients deficient in sedoheptulose-7-kinase, sedoheptulose is phosphorylated by fructokinase to sedoheptulose 1-phosphate. Cleavage of the latter by aldolase B would lead to the formation of erythrose, which would then be reduced to erythritol. [Copyright &y& Elsevier]

Abstract: Besides its essential role at regulating neural functions through cyclic GMP, nitric oxide is emerging as an endogenous physiological modulator of energy conservation for the brain. Thus, nitric oxide inhibits cytochrome c oxidase activity in neurones and glia, resulting in down-regulation of mitochondrial energy production. The subsequent increase in AMP facilitates the activation of 5′-AMP-dependent protein kinase, which rapidly triggers the activation of 6-phosphofructo-1-kinase – the master regulator of the glycolytic pathway – and Glut1 and Glut3 — the main glucose transporters in the brain. In addition, nitric oxide activates glucose-6-phosphate dehydrogenase, the first and rate-limiting step of the pentose–phosphate pathway. Here, we review recent evidences suggesting that nitric oxide exerts a fine control of neuronal energy metabolism by tuning the balance of glucose-6-phosphate consumption between glycolysis and pentose–phosphate pathway. This may have important implications for our understanding of the mechanisms controlling neuronal survival during oxidative stress and bioenergetic crisis. [Copyright &y& Elsevier]

Astrocytes (also, astroglia) consume huge amounts of glucose and produce lactate regardless of sufficient oxygen availability, indicating a high capacity for aerobic glycolysis. Glycolysis in astrocytes is activated in accordance with neuronal excitation and leads to increases in the release of lactate from astrocytes. Although the fate of this lactate remains somewhat controversial, it is believed to fuel neurons as an energy substrate. Besides providing lactate, astrocytic glycolysis plays an important role in neuroprotection. Among the minor pathways of glucose metabolism, glucose flux to the pentose-phosphate pathway (PPP), a major shunt pathway of glycolysis, is attracting research interest. In fact, PPP activity in astrocytes is five to seven times higher than that in neurons. The astrocytic PPP plays a key role in protecting neurons against oxidative stress by providing neurons with a reduced form of glutathione, which is necessary to eliminate reactive oxygen species. Therefore, enhancing astrocytic glycolysis might promote neuronal protection during acute ischemic stroke. Contrariwise, the dysfunction of astrocytic glycolysis and the PPP have been implicated in the pathogenesis of various neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis, since mitochondrial dysfunction and oxidative stress trigger and accelerate disease progression. [ABSTRACT FROM AUTHOR]

Activity of the pentose-phosphate pathway in several rat tissues was investigated, developing a new method that gives the activity of each phase (oxidative and non-oxidative) as well as the whole pathway separately. Our results demonstrate that this method is easy to carry out and that it has not the problems of indirect determinations of the previous ones. The activities of the oxidative and non-oxidative phases assayed separately gives us new information on the design of the pathway in the different tissues, from which several conclusions about the physiological role of this pathway can be derived. In all cases the activity of the oxidative phase was much higher than the non-oxidative one, and the global activity of the whole pathway was the same as the activity of the non-oxidative phase. The highest activity was found in lactating mammary gland and adipose tissue. Lung and liver showed to have a moderately high activity. Brain, kidney, skeletal muscle, and intestinal mucosa showed to have also a significant activity although less than other tissues. The switch in the mammary gland from the non-lactating state to the lactating one causes a very high increase of activity of 22 times, remaining the same ratio between the activity of the two phases. [ABSTRACT FROM AUTHOR]

The pentose phosphate pathway plays several key roles in metabolism including supply of biosynthetic carbon skeletons and reducing power. Previous research has focused on determining the fluxes through the reactions of this pathway using carbon-labeled substrates and models that make certain assumptions about the reversibility of the transketolase and transaldolase reactions in the nonoxidative pathway. These assumptions, however, have resulted in inconsistencies between the predicted carbon label distributions using these models and those determined experimentally. A general metabolic reaction network model developed in this paper and applied to the pentose phosphate pathway not only incorporates reaction reversibility but also accounts for the effect of individually varying extents of reaction reversibility on labeled carbon fractional enrichment values for intermediate metabolites. In addition, an algorithm is presented that can be used to calculate the three individual transaldolase and transketolase extents of reversibility. The results of this method show that varying extents of reaction reversibility have an observable effect on the metabolite carbon label distributions which can in turn affect flux calculation for other parts of the metabolic network such as the tricarboxylic acid cycle. In addition, the observability of reversibility extent and accuracy of flux calculations depend on the particular choice of metabolite carbon enrichments measured. In particular, [6-13C]hexose 6-phosphate and [4-13C]erythrose 4-phosphate carbon enrichment values resulting from [1-13C]glucose feeding contained more information as compared to those from ribose 5-phosphate. This analysis was applied to literature data of metabolite carbon labeling that resulted from supplying either 13C- or 14C-enriched substrates to several cell types growing under various conditions. The specific activities of metabolite carbon atoms... [ABSTRACT FROM AUTHOR]

Plastids from roots of barley ( Hordeum vulgare L.) seedlings were isolated by discontinuous Percoll-gradient centrifugation. Coinciding with the peak of nitrite reductase (NiR; EC 1.7.7.1, a marker enzyme for plastids) in the gradients was a peak of a glucose-6-phosphate (Glc6P) and NADP-linked nitrite-reductase system. High activities of phosphohexose isomerase (EC 5.3.1.9) and phosphoglucomutase (EC 2.7.5.1) as well as glucose-6-phosphate dehydrogenase (Glc6PDH; EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) were also present in the isolated plastids. Thus, the plastids contained an overall electron-transport system from NADPH coupled with Glc6PDH and 6PGDH to nitrite, from which ammonium is formed stoichiometrically. However, NADPH alone did not serve as an electron donor for nitrite reduction, although NADPH with Glc6P added was effective. Benzyl and methyl viologens were enzymatically reduced by plastid extract in the presence of Glc6P+ NADP. When the plastids were incubated with dithionite, nitrite reduction took place, and ammonium was formed stoichiometrically. The results indicate that both an electron carrier and a diaphorase having ferredoxin-NADP reductase activity are involved in the electron-transport system of root plastids from NADPH, coupled with Glc6PDH and 6PGDH, to nitrite. [ABSTRACT FROM AUTHOR]

Plastids were separated from extracts of pea ( Pisum sativum L.) roots by sucrose-density-gradient centrifugation. The incubation of roots of intact pea seedlings in solutions containing 10 mM KNO resulted in increased plastid activity of nitrite reductase and to a lesser extent glutamine synthetase. There were also substantial increases in the activity of glucose-6-phosphate and 6-phosphogluconate dehydrogenases. No other plastid-located enzymes of nitrate assimilation or carbohydrate oxidation showed evidence of increased activity in response to the induction of nitrate assimilation. Studies with [1-C]-and [6-C]glucose indicated that there was an increased flow of carbon through the plastid-located pentose-phosphate pathway concurrent with the induction of nitrate assimilation. It is suggested that there is a close interaction through the supply and demand for reductant between the pathway of nitrite assimilation and the pentose-phosphate pathway located in the plastid. [ABSTRACT FROM AUTHOR]

Isozymes of hexose-phosphate isomerase (HPI; EC 5.3.1.9), pyruvate kinase (PK; EC 2.7.1.40) and 6-phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) have been detected in the developing cotyledons of soybean ( Glycine max (L.) Merr.), safflower ( Carthamnus tinctorius L.) and sunflower ( Helianthus annuus L.). In each seed there are two isozymes each of PK and HPI. The isozyme patterns of 6PGDH are more complex: soybean has two forms of the enzyme, safflower three, and sunflower six. In each tissue, at least 25% of the activity of each of the three enzymes is in the plastids. This supports the proposal that the glycolytic and pentose-phosphate pathways are operating in the plastids and that the plastids are the site of long-chain fatty-acid biosynthesis in developing oilseeds. [ABSTRACT FROM AUTHOR]

We have isolated a cDNA encoding transaldolase, an enzyme of the pentose-phosphate pathway, from potato ( Solanum tuberosum). The 1.5 kb cDNA encodes a protein of 438 amino acid residues with a molecular mass of 47.8 kDa. When the potato cDNA was expressed in Escherichia coli a 45 kDa protein with transaldolase activity was produced. The first 62 amino acids of the deduced amino acid sequence represent an apparent plastid transit sequence. While the potato transaldolase has considerable similarity to the enzyme from cyanobacteria and Mycobacterium leprae, similarity to the conserved transaldolase enzymes from humans, E. coli and Saccharomyces cerevisiae is more limited. Northern analysis indicated that the transaldolase mRNA accumulated in tubers in response to wounding. Probing the RNA from various potato tissues indicated that the transaldolase mRNA accumulation to higher levels in the stem of mature potato plants than in either leaves or tubers. These data are consistent with a role for this enzyme in lignin biosynthesis. [ABSTRACT FROM AUTHOR]

We have cloned and characterized the two remaining unknown genes of the non-oxidative part of the pentose-phosphate pathway of Saccharomyces cerevisiae encoding the enzymes D-ribulose-5-phosphate 3-epimerase (Rpe1p) and D-ribose-5-phosphate ketol-isomerase (Rki1p). Rpe1p has an unexpected high specific activity of 2148 mU × (mg protein) in crude extracts. Deletion mutants of RPE1 show no enzyme activity and are unable to grow on D-xylulose. Unexpectedly, haploid rki1 deletion mutants are not viable. Functional expression of RKI1 was demonstrated following an increase of gene dosage in the haploid rki1 deletion mutant, which restored viability and specific D-ribose-5-phosphate ketol-isomerase activity. Both enzymes show high similarity to the deduced protein sequences of various open reading frames, expressed sequence tags or cDNAs from different organisms. [ABSTRACT FROM AUTHOR]

Deletion mutants for the yeast transketolase gene TKL1 were constructed by gene replacement. Transketolase activity was below the level of detection in mutant crude extracts. Transketolase protein could be detected as a single protein band of the expected size by Western-blot analysis in wild-type strains but not in the delection mutant. Deletion of TKL1 led to a reduced but distinct growth in synthetic medium without an aromatic amino-acid supplement. We also isolated double and triple mutants for transketolase ( tkl1), transaldolase ( tal1), and glucose 6-phosphate dehydrogenase ( zwf1) by crossing the different mutants. A tal1 tkl1 double mutant grew nearly like wild-type in rich medium. Only the tkl1 zwf1 double and the tal1 tkl1 zwf1 triple mutant grew more slowly than the wild-type in rich medium. This growth defect could be partly alleviated by the addition of xylulose but not ribose. The triple mutant still grew slowly on a synthetic mineral salts medium without a supplement of aromatic amino acids. This suggests the existence of an alternative but limited source of pentose phosphates and erythrose 4-phosphate in the tkl1 zwf1 double mutants. Hybridization with low stringency showed the existence of a sequence with homology to transketolase, possibly a second gene. [ABSTRACT FROM AUTHOR]

The CO-output in Yoshida ascites-tumour cells is markedly decreased, when washed ascites-tumour cells are incubated in vitro with [1-C]-glucose in the presence of 6-AN. Inhibition of CO-output increases with increasing concentrations of the drug. Similar results are obtained, when the drug (10, 25 or 50 mg/kg body weight) is administered intraperitoneally into mice bearing ascites-tumour and the ascites cells 9 h after treatment are incubated in vitro with [1-C]-glucose. Glucose-uptake in vitro is likewise lowered following treatment with 6-AN (50 mg/kg body weight). Measurements of metabolic intermediates in homogenates of such pretreated ascites-tumour cells reveal an immense accumulation of 6-phosphogluconate (70-fold) paralleled by a moderate increase in the content of glucose-6-phosphate (3-4-fold). The contents of glucose-1-phosphate and fructose-6-phosphate increase concomitantly. A 6-7-fold increase in the content of the triose phosphates (glyceraldehyde-3-phosphate and dihydroxyacetone phosphate) with a concomitant 5-6-fold increase in the content of fructose-1,6-diphosphate is also observed, whereas the contents of glycerol-1-phosphate, pyruvate, lactate, malate, and ATP are decreased; that of phosphoenolpyruvate is slightly raised. The ratio of glucose-6-phosphate to fructose-6-phosphate increases slightly from 3.5 for control assay systems to 4.2 following treatment with the drug. This is no significant increase and may suggest no inhibition of glycolysis by 6-phosphogluconate at the phosphoglucose isomerase level. The simultaneous intraperitoneal injection of nicotinamide (50 mg/kg body weight) abolishes or at least minimizes the metabolic effects caused by 6-AN. The data presented suggest inhibition of glycolysis and more effectively of the pentose phosphate pathway in ascites-tumour cells by in vivo synthesized NAD(P)-analogues of 6-AN. [ABSTRACT FROM AUTHOR]