Dissolved oxygen and ammonia affect ammonia production via GDH/AMPK signaling pathway and alter flesh quality in Chinese perch (Siniperca chuatsi)

The dissolved oxygen (DO) and ammonia are crucial to the growth of Chinese perch (Siniperca chuatsi). Information on the effects of DO and total ammonia nitrogen (TAN) in regulating ammonia nitrogen excretion and flesh quality in Chinese perch is scanty. This study aimed to evaluate the effects of dissolved DO at oxygen levels of 3 mg/L and 9 mg/L, as well as the TAN concentrations of 0.3 mg/L and 0.9 mg/L on ammonia excretion and flesh quality. Results showed that the ammonia contents in plasma, muscle, and liver of the 9 mg/L DO group were significantly higher than those of the 3 mg/L DO group (P < 0.05). However, the expression of AMPK-related signaling pathway genes (gdh, lkb1, and ampd) and flesh quality indicators (gumminess, chewiness, hardness) in the 9 mg/L DO group were significantly lower than those in the 3 mg/L DO group. Under long-term exposure to 0.9 mg/L TAN, the ammonia contents in plasma and gill filaments, as well as muscle flesh quality (resilience, gumminess, chewiness, cohesiveness), were significantly lower than those in the 0.3 mg/L TAN group (P < 0.05). However, the activities of GDH and AMPD enzymes in the 0.9 mg/L TAN group were significantly higher than those in the 0.3 mg/L TAN group. In summary, when fish are exposed to 3 mg/L DO and 0.9 mg/L TAN in the environment for a long time, their amino acids are used for transamination and deamination, resulting in insufficient energy supply for Chinese perch, whereas 9 mg/L DO and 0.9 mg/L TAN caused deterioration of the flesh quality.

A comparative analysis of fruit fly and human glutamate dehydrogenases in Drosophila melanogaster sperm development

Glutamate dehydrogenases are enzymes that take part in both amino acid and energy metabolism. Their role is clear in many biological processes, from neuronal function to cancer development. The putative testis-specific Drosophila glutamate dehydrogenase, Bb8, is required for male fertility and the development of mitochondrial derivatives in spermatids. Testis-specific genes are less conserved and could gain new functions, thus raising a question whether Bb8 has retained its original enzymatic activity. We show that while Bb8 displays glutamate dehydrogenase activity, there are significant functional differences between the housekeeping Gdh and the testis-specific Bb8. Both human GLUD1 and GLUD2 can rescue the bb8 ms mutant phenotype, with superior performance by GLUD2. We also tested the role of three conserved amino acids observed in both Bb8 and GLUD2 in Gdh mutants, which showed their importance in the glutamate dehydrogenase function. The findings of our study indicate that Drosophila Bb8 and human GLUD2 could be novel examples of convergent molecular evolution. Furthermore, we investigated the importance of glutamate levels in mitochondrial homeostasis during spermatogenesis by ectopic expression of the mitochondrial glutamate transporter Aralar1, which caused mitochondrial abnormalities in fly spermatids. The data presented in our study offer evidence supporting the significant involvement of glutamate metabolism in sperm development.

Heat shock protein 70, glutamate dehydrogenase, and angiotensin-converting enzyme of Bombyx mori mediate the cell attachment of Cypovirus 1

Dendrolimus punctatus causes great damage to pine forests worldwide. Dendrolimus punctatus cypovirus 1 (DpCPV-1) is an important pathogen of D. punctatus. However, the mechanism of DpCPV-1 cell entry has not been elucidated. In this study, we revealed that both GTase and MTase domains of VP3 (B-spike) and VP4 (A-spike) of DpCPV-1 interacted with the midgut proteins of Bombyx mori. Binding and competition assays revealed that GTase, MTase and VP4 played roles as viral attachment proteins. Far-Western blotting and LC-MS/MS analyses identified that heat shock protein 70 (BmHSP70), glutamate dehydrogenase (BmGDH), and angiotensin-converting enzyme (BmACE) in the midgut proteins as ligand candidates of the viral attachment proteins, and this was further verified by co-immunoprecipitation and fluorescence co-localization assays. Viral binding to the host midgut in vitro was inhibited by pre-treating B. mori midgut proteins with anti-BmHSP70, anti-BmGDH, anti-BmACE antibodies singly and in combination. Incubating DpCPV-1 virions with prokaryotically expressed BmHSP70, BmGDH, and BmACE also decreased viral attachment to the host midgut. In vivo bioassays revealed that viral infection in Helicoverpa armigera was partially neutralized by BmHSP70, BmGDH, and BmACE. Taking together, we concluded that HSP70, GDH, and ACE mediate DpCPV attachment and entry via binding to the viral attachment proteins, VP3 and VP4. The findings provide foundation for further understanding the entry mechanisms of cypoviruses.

Preanthesis changes in freeze resistance, relative water content, and ovary growth preempt bud phenology and signify dormancy release of sour cherry floral buds

Growing degree hours (GDH) predicted floral bud development of 'Montmorency' sour cherry and explained changes in lethal temperatures (LT₅₀) that preempted any visible changes in bud phenology. The gradual warming during late winter and early spring promotes floral bud development and, concomitantly, the de-acclimation of Prunus sp. flowers. In fact, once ecodormancy releases, an approximate 20 °C loss of hardiness occurs prior to any distinguishable changes in external bud phenology. The aim of the following work was to characterize the physiological changes of 'Montmorency' sour cherry floral buds as they transition from endo- and ecodormancy and resume growth, and to determine whether physiological and anatomical characteristics within the buds preempt or signify dormancy release to enable a better prediction of freeze susceptibility. Here, we present a developmental timeline of the preanthesis changes of 'Montmorency' floral buds, ovaries and anthers over 2 years following their completion of chilling and relate these changes to growing degree hours (GDH) and the lethal temperature (LT₅₀) of flowers. Changes in bud dry weight (DW), fresh weight (FW), volume, and external phenology stage including the percentage of green color development of bud scales were predicted by heat accumulation but were not early predictors of the increasing freeze susceptibility of pistils. Between endodormancy and green tip stage, ovary volume increased nearly threefold and relative water content (RWC) increased from ~ 45 to 70% in both years. A linear mixed regression model indicated that RWC and the interaction between RWC and ovary growth were significant predictors of LT₅₀. Importantly, the loss of ~ 20 °C of freeze resistance occurred between 45 and 57% RWC and preceded any detectable changes in bud phenology. Microsporogenesis was observed after dormancy release when measurable changes in the ovary and bud RWC had already occurred. A GDH model estimated freeze sensitivity of pistils and explained 93% of the variation in LT₅₀ during preanthesis development. A simple GDH model to predict critical freeze temperature of pistils should aid producers to manage frost protection.

Enhanced Fenton Reaction for Xenobiotic Compounds and Lignin Degradation Fueled by Quinone Redox Cycling by Lytic Polysaccharide Monooxygenases

The Fenton reaction is considered to be of great significance in the initial attack of lignocellulose in wood-decaying fungi. Quinone redox cycling is the main way to induce the Fenton reaction in fungi. We show that lytic polysaccharide monooxygenases (LPMOs), through LPMO-catalyzed oxidation of hydroquinone, can efficiently cooperate with glucose dehydrogenase (GDH) to achieve quinone redox cycling. The LPMO/GDH system can enhance Fe3+-reducing activity, H2O2 production, and hydroxyl radical generation, resulting in a fueled Fenton reaction. The system-generated hydroxyl radicals exhibited a strong capacity to decolorize different synthetic dyes and degrade lignin. Our results reveal a potentially critical connection between LPMOs and the Fenton reaction, suggesting that LPMOs could be involved in xenobiotic compound and lignin degradation in fungi. This new role of LPMOs may be exploited for application in biorefineries.

Vital Role of Glutamate Dehydrogenase Gene in Ammonia Detoxification and the Association Between its SNPs and Ammonia Tolerance in Sinonovacula constricta

Increasing evidence has revealed accumulated ammonia will cause adverse effects on the growth, reproduction, and survival of aquatic animals. As a marine benthic mollusk, the razor clam Sinonovacula constricta shows better growth and survival under high ammonia nitrogen environment. However, little is known about its adaptation mechanisms to high ammonia stress in an integrated mariculture system. In this study, we analyzed the association between the polymorphism of glutamate dehydrogenase gene (GDH), a key gene involved in ammonia nitrogen detoxification, and ammonia tolerance. The results showed that 26 and 22 single-nucleotide polymorphisms (SNPs) of GDH in S. constricta (denoted as Sc-GDH) were identified from two geographical populations, respectively. Among them, two SNPs (c.323T > C and c.620C > T) exhibited a significant and strong association with ammonia tolerance, suggesting that Sc-GDH gene could serve as a potential genetic marker for molecular marker–assisted selection to increase survival rate and production of S. constricta. To observe the histological morphology and explore the histocellular localization of Sc-GDH, by paraffin section and hematoxylin–eosin staining, the gills were divided into gill filament (contains columnar and flattened cells) and gill cilia, whereas hepatopancreas was made up of individual hepatocytes. The results of immunohistochemistry indicated that the columnar cells of gill filaments and the endothelial cells of hepatocytes were the major sites for Sc-GDH secretion. Under ammonia stress (180 mg/L), the expression levels of Sc-GDH were extremely significantly downregulated at 24, 48, 72, and 96 h (P < 0.01) after RNA interference. Thus, we can speculate that Sc-GDH gene may play an important role in the defense process against ammonia stress. Overall, these findings laid a foundation for further research on the adaptive mechanisms to ammonia–nitrogen tolerance for S. constricta.

How to easily detect plant NADH-glutamate dehydrogenase (GDH) activity? A simple and reliable in planta procedure suitable for tissues, extracts and heterologous microbial systems

Plant NADH glutamate dehydrogenase (GDH) is an intriguing enzyme, since it is involved in different metabolic processes owing to its reversible (anabolic/catabolic) activity and due to the oligomeric nature of the enzyme, that gives rise to several isoforms. The complexity of GDH isoenzymes pattern and the variability of the spatial and temporal localization of the different isoforms have limited our comprehension of the physiological role of GDH in plants. Genetics, immunological, and biochemical approaches have been used until now in order to shed light on the regulatory mechanism that control GDH expression in different plant systems and environmental conditions. We describe here the validation of a simple in planta GDH activity staining procedure, providing evidence that it might be used, with different purposes, to determine GDH expression in plant organs, tissues, extracts and also heterologous systems.

Glutamate-glutamine homeostasis is perturbed in neurons and astrocytes derived from patient iPSC models of frontotemporal dementia

Frontotemporal dementia (FTD) is amongst the most prevalent early onset dementias and even though it is clinically, pathologically and genetically heterogeneous, a crucial involvement of metabolic perturbations in FTD pathology is being recognized. However, changes in metabolism at the cellular level, implicated in FTD and in neurodegeneration in general, are still poorly understood. Here we generate induced human pluripotent stem cells (hiPSCs) from patients carrying mutations in CHMP2B (FTD3) and isogenic controls generated via CRISPR/Cas9 gene editing with subsequent neuronal and glial differentiation and characterization. FTD3 neurons show a dysregulation of glutamate-glutamine related metabolic pathways mapped by ¹³C-labelling coupled to mass spectrometry. FTD3 astrocytes show increased uptake of glutamate whilst glutamate metabolism is largely maintained. Using quantitative proteomics and live-cell metabolic analyses, we elucidate molecular determinants and functional alterations of neuronal and glial energy metabolism in FTD3. Importantly, correction of the mutations rescues such pathological phenotypes. Notably, these findings implicate dysregulation of key enzymes crucial for glutamate-glutamine homeostasis in FTD3 pathogenesis which may underlie vulnerability to neurodegeneration. Neurons derived from human induced pluripotent stem cells (hiPSCs) of patients carrying mutations in CHMP2B (FTD3) display major metabolic alterations compared to CRISPR/Cas9 generated isogenic controls. Using quantitative proteomics, ¹³C-labelling coupled to mass spectrometry metabolic mapping and seahorse analyses, molecular determinants and functional alterations of neuronal and astrocytic energy metabolism in FTD3 were characterized. Our findings implicate dysregulation of glutamate-glutamine homeostasis in FTD3 pathogenesis. In addition, FTD3 neurons recapitulate glucose hypometabolism observed in FTD patient brains. The impaired mitochondria function found here is concordant with disturbed TCA cycle activity and decreased glycolysis in FTD3 neurons. FTD3 neuronal glutamine hypermetabolism is associated with up-regulation of PAG expression and, possibly, ROS production. Distinct compartments of glutamate metabolism can be suggested for the FTD3 neurons. Endogenous glutamate generated from glutamine via PAG may enter the TCA cycle via AAT (left side of neuron) while exogenous glutamate taken up from the extracellular space may be incorporated into the TCA cycle via GDH (right side of the neuron) FTD3 astrocytic glutamate uptake is upregulated whilst glutamate metabolism is largely maintained. Finally, pharmacological reversal of glutamate hypometabolism manifesting from decreased GDH expression should be explored as a novel therapeutic intervention for treating FTD3.

Glutamate dehydrogenase plays an important role in ammonium detoxification by submerged macrophytes

Ammonium is a paradoxical chemical because it is a nutrient but also damages ecosystems at high concentration. As the most eco-friendly method of water restoration, phytoremediation technology still faces great challenges. To provide more theoretical support, we exploited six common submerged macrophytes and selected the most ammonium-tolerant and -sensitive species; then further explored and compared the mechanisms underlying ammonium detoxification. Our results showed the activity of glutamate dehydrogenase (GDH) in the ammonium-tolerant species Myriophyllum spicatum leaves performed a dose-response curve (increased 169% for NADH-dependent GDH and 103% for NADPH-dependent GDH) with the [NH₄⁺-N] increasing from 0 to 100 mg/L while glutamine synthetase (GS) activity slightly changed. But for the ammonium-sensitive species, Potamogeton lucens, the activity of GDH recorded no major changes, while the GS increased slightly (17%). Based on this, we conclude that the alternative pathway of GDH is more important than the pathway catalyzed by GS in determining the tolerance of submerged macrophytes to high ammonium concentration (up to 100 mg N/L). Our present study identifies submerged macrophytes that are tolerant of high concentrations of ammonium and provides mechanistic support for practical water restoration by aquatic plants.

Prospective Evaluation of the mariPOC Test for Detection of Clostridioides difficile Glutamate Dehydrogenase and Toxins A/B

The objective of this study was to evaluate a novel automated random-access test, mariPOC CDI (ArcDia Ltd., Finland), for the detection of Clostridioides difficile glutamate dehydrogenase (GDH) and toxins A and B directly from fecal specimens. The mariPOC test was compared with both the GenomEra C. difficile PCR assay (Abacus Diagnostica Oy, Finland) and the TechLab C. diff Quik Chek Complete (Alere Inc.; now Abbot) membrane enzyme immunoassay (MEIA). Culture and the Xpert C. difficile assay (Cepheid Inc., USA) were used to resolve discrepant results. In total, 337 specimens were tested with the mariPOC CDI test and GenomEra PCR. Of these specimens, 157 were also tested with the TechLab MEIA. The sensitivity of the mariPOC test for GDH was slightly lower (95.2%) than that obtained with the TechLab assay (100.0%), but no toxin-positive cases were missed. The sensitivity of the mariPOC test for the detection of toxigenic C. difficile by analyzing toxin expression was better (81.6%) than that of the TechLab assay (71.1%). The analytical specificities for the mariPOC and the TechLab tests were 98.3% and 100.0% for GDH and 100.0% and 99.2% for toxin A/B, respectively. The analytical specificity of the GenomEra method was 100.0%. The mariPOC and TechLab GDH tests and GenomEra PCR had high negative predictive values of 99.3%, 98.3%, and 99.7%, respectively, in excluding infection with toxigenic C. difficile The mariPOC toxin A/B test and GenomEra PCR had an identical analytical positive predictive value of 100%, providing highly reliable information about toxin expression and the presence of toxin genes, respectively.

Non-oncogene Addiction to SIRT3 Plays a Critical Role in Lymphomagenesis

Diffuse large B cell lymphomas (DLBCLs) are genetically heterogeneous and highly proliferative neoplasms derived from germinal center (GC) B cells. Here, we show that DLBCLs are dependent on mitochondrial lysine deacetylase SIRT3 for proliferation, survival, self-renewal, and tumor growth in vivo regardless of disease subtype and genetics. SIRT3 knockout attenuated B cell lymphomagenesis in VavP-Bcl2 mice without affecting normal GC formation. Mechanistically, SIRT3 depletion impaired glutamine flux to the TCA cycle via glutamate dehydrogenase and reduction in acetyl-CoA pools, which in turn induce autophagy and cell death. We developed a mitochondrial-targeted class I sirtuin inhibitor, YC8-02, which phenocopied the effects of SIRT3 depletion and killed DLBCL cells. SIRT3 is thus a metabolic non-oncogene addiction and therapeutic target for DLBCLs.

Glutamate dehydrogenase is essential to sustain neuronal oxidative energy metabolism during stimulation

The enzyme glutamate dehydrogenase (GDH; Glud1) catalyzes the (reversible) oxidative deamination of glutamate to α-ketoglutarate accompanied by a reduction of NAD⁺ to NADH. GDH connects amino acid, carbohydrate, neurotransmitter and oxidative energy metabolism. Glutamine is a neurotransmitter precursor used by neurons to sustain the pool of glutamate, but glutamine is also vividly oxidized for support of energy metabolism. This study investigates the role of GDH in neuronal metabolism by employing the Cns- Glud1^-/- mouse, lacking GDH in the brain (GDH KO) and metabolic mapping using ¹³C-labelled glutamine and glucose. We observed a severely reduced oxidative glutamine metabolism during glucose deprivation in synaptosomes and cultured neurons not expressing GDH. In contrast, in the presence of glucose, glutamine metabolism was not affected by the lack of GDH expression. Respiration fuelled by glutamate was significantly lower in brain mitochondria from GDH KO mice and synaptosomes were not able to increase their respiration upon an elevated energy demand. The role of GDH for metabolism of glutamine and the respiratory capacity underscore the importance of GDH for neurons particularly during an elevated energy demand, and it may reflect the large allosteric activation of GDH by ADP.

Effects of antiepileptic drugs on mitochondrial functions, morphology, kinetics, biogenesis, and survival

OBJECTIVES

Antiepileptic drugs (AEDs) exhibit adverse and beneficial effects on mitochondria, which have a strong impact on the treatment of patients with a mitochondrial disorder (MID) with epilepsy (mitochondrial epilepsy). This review aims at summarizing and discussing recent findings concerning the effect of AEDs on mitochondrial functions and the clinical consequences with regard to therapy of mitochondrial epilepsy and of MIDs in general.

METHODS

Literature review.

RESULTS

AEDs may interfere with the respiratory chain, with non-respiratory chain enzymes, carrier proteins, or mitochondrial biogenesis, with carrier proteins, membrane-bound channels or receptors and the membrane potential, with anti-oxidative defense mechanisms, with morphology, dynamics and survival of mitochondria, and with the mtDNA. There are AEDs of which adverse effects outweigh beneficial effects, such as valproic acid, carbamazepine, phenytoin, or phenobarbital and there are AEDs in which beneficial effects dominate over mitochondrial toxic effects, such as lamotrigine, levetiracetam, gabapentin, or zonisamide. However, from most AEDs only little is known about their interference with mitochondria.

CONCLUSIONS

Mitochondrial epilepsy might be initially treated with AEDs with low mitochondrial toxic potential. Only in case mitochondrial epilepsy is refractory to these AEDs, AEDs with higher mitochondrial toxic potential might be tried. In patients carrying POLG1 mutations AEDs with high mitochondrial toxic potential are contraindicated.

Divergent Metabolic Regulation of Autophagy and mTORC1-Early Events in Alzheimer's Disease?

Alzheimer's disease (AD) is a progressive disease associated with the production and deposition of amyloid β-peptide (Aβ) aggregates and neurofibrillary tangles, which lead to synaptic and neuronal damage. Reduced autophagic flux has been widely associated with the accumulation of autophagic vacuoles (AV), which has been proposed to contribute to aggregate build-up observed in AD. As such, targeting autophagy regulation has received wide review, where an understanding as to how this mechanism can be controlled will be important to neuronal health. The mammalian target of rapamycin complex 1 (mTORC1), which was found to be hyperactive in AD brain, regulates autophagy and is considered to be mechanistically important to aberrant autophagy in AD. Hormones and nutrients such as insulin and leucine, respectively, positively regulate mTORC1 activation and are largely considered to inhibit autophagy. However, in AD brain there is a dysregulation of nutrient metabolism, linked to insulin resistance, where a role for insulin treatment to improve cognition has been proposed. Recent studies have highlighted that mitochondrial proteins such as glutamate dehydrogenase and the human branched chain aminotransferase protein, through metabolism of leucine and glutamate, differentially regulate mTORC1 and autophagy. As the levels of the hBCAT proteins are significantly increased in AD brain relative to aged-matched controls, we discuss how these metabolic pathways offer new potential therapeutic targets. In this review article, we highlight the core regulation of autophagy through mTORC1, focusing on how insulin and leucine will be important to consider in particular with respect to our understanding of nutrient load and AD pathogenesis.

Expression and prognostic value of glutamate dehydrogenase in extrahepatic cholangiocarcinoma patients

Glutamate dehydrogenase (GDH) produces a precursor to glutathione, an important molecule in maintaining cellular redox balance and the cancerous characteristics of tumor cells through intracellular signaling pathways. However, the underlying molecular mechanisms linking glutamate dehydrogenase and extrahepatic cholangiocarcinoma have not been elucidated yet. Herein, we examined GDH expression levels and evaluated its potential correlations with prognosis. Meanwhile, the therapeutic value of GDH targeting the Smad pathways in extrahepatic cholangiocarcinoma was explored. Immunohistochemical studies revealed that GDH expression level was correlated to CD34 expression, cellular differentiation, the presence or absence of capsular and vascular invasion, lymph node metastasis, neural invasion and patient age. Kaplan-Meier survival analysis and COX proportional hazards models demonstrated that the prognosis was closely associated with GDH expression, CD34 positivity, nerve infiltration and cell differentiation. GDH silencing significantly reduced the proliferation, migratory potential and invasive capability. We also demonstrated that GDH promoted cell proliferation and metastasis potentially through Smad-mediated induction of TGF-β signaling pathway. Therefore, GDH may be an important prognostic indicator and may provide a new target for novel treatments of extrahepatic cholangiocarcinoma.

The Glutamate Dehydrogenase Pathway and Its Roles in Cell and Tissue Biology in Health and Disease

Glutamate dehydrogenase (GDH) is a hexameric enzyme that catalyzes the reversible conversion of glutamate to α-ketoglutarate and ammonia while reducing NAD(P)⁺ to NAD(P)H. It is found in all living organisms serving both catabolic and anabolic reactions. In mammalian tissues, oxidative deamination of glutamate via GDH generates α-ketoglutarate, which is metabolized by the Krebs cycle, leading to the synthesis of ATP. In addition, the GDH pathway is linked to diverse cellular processes, including ammonia metabolism, acid-base equilibrium, redox homeostasis (via formation of fumarate), lipid biosynthesis (via oxidative generation of citrate), and lactate production. While most mammals possess a single GDH1 protein (hGDH1 in the human) that is highly expressed in the liver, humans and other primates have acquired, via duplication, an hGDH2 isoenzyme with distinct functional properties and tissue expression profile. The novel hGDH2 underwent rapid evolutionary adaptation, acquiring unique properties that enable enhanced enzyme function under conditions inhibitory to its ancestor hGDH1. These are thought to provide a biological advantage to humans with hGDH2 evolution occurring concomitantly with human brain development. hGDH2 is co-expressed with hGDH1 in human brain, kidney, testis and steroidogenic organs, but not in the liver. In human cerebral cortex, hGDH1 and hGDH2 are expressed in astrocytes, the cells responsible for removing and metabolizing transmitter glutamate, and for supplying neurons with glutamine and lactate. In human testis, hGDH2 (but not hGDH1) is densely expressed in the Sertoli cells, known to provide the spermatids with lactate and other nutrients. In steroid producing cells, hGDH1/2 is thought to generate reducing equivalents (NADPH) in the mitochondria for the biosynthesis of steroidal hormones. Lastly, up-regulation of hGDH1/2 expression occurs in cancer, permitting neoplastic cells to utilize glutamine/glutamate for their growth. In addition, deregulation of hGDH1/2 is implicated in the pathogenesis of several human disorders.

Hypoxia promotes mitochondrial glutamine metabolism through HIF1α-GDH pathway in human lung cancer cells

Drug-resistance is common in human lung cancer therapy. Hypoxia remarkably contributes to drug-resistance in lung cancer but the underlying mechanism remains elusive. Here we demonstrate that hypoxia-induced glutamine metabolism is involved in drug resistance in lung cancer cells. Hypoxia increases glutamine up-take, glutamate to α-ketoglutarate flux and the generation of ATP in lung cancer cells by up-regulating the expression of glutamate dehydrogenase (GDH). Hypoxia-induced expression of GDH relies on the up-regulation of HIF1α but not HIF2α. HIF1α binds the promoter of GDH and promotes the transcription of GDH gene in lung cancer cells. Finally, we show that GDH represses cisplatin-induced cell apoptosis and repression of colony formation, indicating that GDH contributes to drug-resistance in lung cancer cells. In conclusion, HIF1α-GDH pathway regulates glutamine metabolism and ATP production upon hypoxia stress and contributes to drug-resistance in human lung cancer cells.

Laboratory Experience with the Liaison Analyzer in the Diagnosis of Clostridium Difficile-Associated Diarrhea

Background

Chemiluminescent or enzyme-linked fluorescent immunoassays are commonly used to diagnose Clostridium difficile-associated diarrhea.

Methods

The LIAISON analyzer (DiaSorin, Italy) was compared to miniVIDAS (bioMérieux, France) and, furthermore, to culture of toxigenic strains. In total, 249 native stool samples were analyzed. Sensitivities, specificities, and positive and negative predictive values were investigated. Furthermore, performance under routine conditions was assessed.

Results

The glutamate dehydrogenase chemiluminescent immunoassay (GDH-CLIA) assay revealed a high sensitivity and negative predictive value. The toxins A&B assays exhibited approximately the same low sensitivity and high specificity. Technical drawbacks experienced with the LIAISON analyzer in 48% of the analyses considerably delayed the time to the first diagnostic report and interfered with laboratory routine workflow.

Conclusion

The analytical performance of the investigated platforms should be reflected in the context of implementation into the laboratory workflow.

Growing degree hours - a simple, accurate, and precise protocol to approximate growing heat summation for grapevines

Despite its low accuracy and consistency, growing degree days (GDD) has been widely used to approximate growing heat summation (GHS) for regional classification and phenological prediction. GDD is usually calculated from the mean of daily minimum and maximum temperatures (GDDmm) above a growing base temperature (T gb). To determine approximation errors and accuracy, daily and cumulative GDDmm was compared to GDD based on daily average temperature (GDDavg), growing degree hours (GDH) based on hourly temperatures, and growing degree minutes (GDM) based on minute-by-minute temperatures. Finite error, due to the difference between measured and true temperatures above T gb is large in GDDmm but is negligible in GDDavg, GDH, and GDM, depending only upon the number of measured temperatures used for daily approximation. Hidden negative error, due to the temperatures below T gb when being averaged for approximation intervals larger than measuring interval, is large in GDDmm and GDDavg but is negligible in GDH and GDM. Both GDH and GDM improve GHS approximation accuracy over GDDmm or GDDavg by summation of multiple integration rectangles to reduce both finite and hidden negative errors. GDH is proposed as the standardized GHS approximation protocol, providing adequate accuracy and high precision independent upon T gb while requiring simple data recording and processing.

Key enzymes catalyzing glycerol to 1,3-propanediol

Biodiesel can replace petroleum diesel as it is produced from animal fats and vegetable oils, and it produces about 10 % (w/w) glycerol, which is a promising new industrial microbial carbon, as a major by-product. One of the most potential applications of glycerol is its biotransformation to high value chemicals such as 1,3-propanediol (1,3-PD), dihydroxyacetone (DHA), succinic acid, etc., through microbial fermentation. Glycerol dehydratase, 1,3-propanediol dehydrogenase (1,3-propanediol-oxydoreductase), and glycerol dehydrogenase, which were encoded, respectively, by dhaB, dhaT, and dhaD and with DHA kinase are encompassed by the dha regulon, are the three key enzymes in glycerol bioconversion into 1,3-PD and DHA, and these are discussed in this review article. The summary of the main research direction of these three key enzyme and methods of glycerol bioconversion into 1,3-PD and DHA indicates their potential application in future enzymatic research and industrial production, especially in biodiesel industry.

Absence of keratin 8 or 18 promotes antimitochondrial autoantibody formation in aging male mice

Human mutations in keratin 8 (K8) and keratin 18 (K18), the intermediate filament proteins of hepatocytes, predispose to several liver diseases. K8-null mice develop chronic liver injury and fragile hepatocytes, dysfunctional mitochondria, and Th2-type colitis. We tested the hypothesis that autoantibody formation accompanies the liver damage that associates with K8/K18 absence. Sera from wild-type control, K8-null, and K18-null mice were analyzed by immunoblotting and immunofluorescence staining of cell and mouse tissue homogenates. Autoantibodies to several antigens were identified in 81% of K8-null male mice 8 mo or older. Similar autoantibodies were detected in aging K18-null male mice that had a related liver phenotype but normal colon compared with K8-null mice, suggesting that the autoantibodies are linked to liver rather than colonic disease. However, these autoantibodies were not observed in nontransgenic mice subjected to 4 chronic injury models. The autoantigens are ubiquitous and partition with mitochondria. Mass spectrometry and purified protein analysis identified, mitochondrial HMG-CoA synthase, aldehyde dehydrogenase, and catalase as the primary autoantigens, and glutamate dehydrogenase and epoxide hydrolase-2 as additional autoantigens. Therefore, absence of the hepatocyte keratins results in production of anti-mitochondrial autoantibodies (AMA) that recognize proteins involved in energy metabolism and oxidative stress, raising the possibility that AMA may be found in patients with keratin mutations that associate with liver and other diseases.

Glucose replaces glutamate as energy substrate to fuel glutamate uptake in glutamate dehydrogenase-deficient astrocytes

Cultured astrocytes treated with siRNA to knock down glutamate dehydrogenase (GDH) were used to investigate whether this enzyme is important for the utilization of glutamate as an energy substrate. By incubation of these cells in media containing different concentrations of glutamate (range 100-500 µM) in the presence or in the absence of glucose, the metabolism of these substrates was studied by using tritiated glutamate or 2-deoxyglucose as tracers. In addition, the cellular contents of glutamate and ATP were determined. The astrocytes were able to maintain physiological levels of ATP regardless of the expression level of GDH and the incubation condition, indicating a high degree of flexibility with regard to regulatory mechanisms involved in maintaining an adequate energy level in the cells. Glutamate uptake was found to be increased in these cells when exposed to increasing levels of extracellular glutamate independently of the GDH expression level. Moreover, increased intracellular glutamate content was observed in the GDH-deficient cells after a 2-hr incubation in the presence of 100 µM glutamate. It is significant that GDH-deficient cells exhibited an increased utilization of glucose in the presence of 250 and 500 µM glutamate, monitored as an increase in the accumulation of tritiated 2-deoxyglucose-6-phosphate. These findings underscore the importance of the expression level of GDH for the ability to utilize glutamate as an energy source fueling its own energy-requiring uptake.

Coimmobilization of l-methioninase and glutamate dehydrogenase: Novel approach for L-homoalanine synthesis

L-Homoalanine, a nonnatural amino acid that is rarely found in human and microorganisms, is used in the synthesis of various medically pivotal antiepileptic drugs and antituberculosis compounds. l-Homoalanine can be synthesized by different enzymatic approaches. In this article, the synthesis of l-homoalanine from l-methionine was explored by coimmobilization of Aspergillus flavipes l-methioninase (AfMETase) and glutamate dehydrogenase (GDH) on polyacrylamide and chitosan. Polyacrylamide coimmobilized AfMETase and GDH displayed a maximum reactivity for the synthesis of homoalanine from l-methionine. The chitosan-coimmobilized AfMETase and GDH retain about 70% of their initial activity of l-homoalanine production by the fifth catalytic reusability cycle as compared with 50% for polyacrylamide coimmobilizate. Catalytic conditions were optimized for the maximum yield of homoalanine. Homoalanine was purified by cationic and anionic chromatographs and the proton nuclear magnetic resonance (H-NMR) analysis of the lyophilized sample displayed a unique chemical structure identical to the authentic homoalanine. Using dependable dual action of AfMETase and GDH immobilized on a solid support is a novel approach for in vitro enzymatic synthesis of l-homoalanine from l-methionine, and the immobilized enzymes can be reused many times without any significant loss of their activities.

Detection of nosocomial Clostridium difficile infections with toxigenic strains despite negative toxin A and B testing on stool samples

A two-step diagnostic algorithm is recommended to detect Clostridium difficile infections; however, samples are regularly found that are glutamate dehydrogenase (GDH) positive but stool toxin negative. In the present single-centre prospective study we focused on these 'difficult-to-interpret' samples and characterized them by anaerobic culture, toxigenic culture, slpA sequence typing and multiplex PCR (GenoType CDiff). The majority of stool toxin A and B-negative samples have been caused by toxigenic strains including ribotype 027. The multiplex PCR was faster and more sensitive compared with culture and allowed preliminary identification of hypervirulent strains in stool samples on the same day.

Resistin and visfatin in steatotic and non-steatotic livers in the setting of partial hepatectomy under ischemia-reperfusion

BACKGROUND & AIMS

This study examined whether the regulation of resistin and visfatin could reduce damage and improve regeneration in both steatotic and non-steatotic livers undergoing partial hepatectomy under ischemia-reperfusion, a procedure commonly applied in clinical practice to reduce bleeding.

METHODS

Resistin and visfatin were pharmacologically modulated in lean and obese animals undergoing partial hepatectomy under ischemia-reperfusion.

RESULTS

No evident role for these adipocytokines was observed in non-steatotic livers. However, obese animals undergoing liver surgery showed increased resistin in liver and plasma, without changes in adipose tissue, together with visfatin downregulation in liver and increment in plasma and adipose tissue. Endogenous resistin maintains low levels of visfatin in the liver by blocking its hepatic uptake from the circulation, thus regulating the visfatin detrimental effects on hepatic damage and regenerative failure. Indeed, the administration of anti-resistin antibodies increased hepatic accumulation of adipocyte-derived visfatin, exacerbating damage and regenerative failure. Interestingly, treatment with anti-visfatin antibodies protected steatotic livers, and similar results were obtained with the concomitant inhibition of resistin and visfatin. Thus, when visfatin was inhibited, the injurious effects of anti-resistin antibodies disappeared. Herein we show that upregulation of visfatin increased NAD levels in the remnant steatotic liver, whereas visfatin inhibition decreased them. These later observations suggest that visfatin may favour synthesis of NAD instead of DNA and induces alterations in amino acid metabolism-urea cycle and NO production, overall negatively affecting liver viability.

CONCLUSIONS

Our results indicate the clinical potential of visfatin blocking-based therapies in steatotic livers undergoing partial hepatectomy with ischemia-reperfusion.

Comparison of ascorbic acid biosynthesis in different tissues of three non-heading Chinese cabbage cultivars

Ascorbic acid (L-AsA) is an important antioxidant in plants and humans. Vegetables are one of the main sources of ascorbic acid for humans. For instance, non-heading Chinese cabbage (Brassica campestris ssp. chinensis Makino) is considered as one of the most important vegetables in south China. To elucidate the mechanism by which AsA accumulates, we systematically investigated the expression profiles of D-mannose/L-galactose pathway-related genes. We also investigated the recycling-related genes and AsA contents in different tissues of three non-heading Chinese cabbage cultivars, 'Suzhouqing', 'Wutacai' and 'Erqing' containing different amounts of AsA. Our results showed that six genes [D-mannose-6-phosphate isomerase 1 (PMI1), GDP-L-galactose phosphorylase 1 (GGP1), GGP2, GGP4, GDP-mannose-3', 5'-epimerase1 (GME1), and GME2] were expressed at high level and ascorbate oxidase (AAO) was expressed at low level. This expression pattern contributes, at least partially, to higher AsA accumulation in the leaves and petioles than in the roots. Eight genes (PMI1, GME, GGP, L-galactose-1-phosphate phosphatase, L-galactose dehydrogenase, L-galactono-1, 4-lactone dehydrogenase, monodehydroascorbate reductase 1, and glutathione reductase1) were also expressed at high level; AAO and ascorbate peroxidase (APX) were expressed at low level. This expression pattern may similarly contribute to higher AsA accumulation in 'Wutacai' and 'Suzhouqing' than in 'Erqing'. Therefore, the high expression levels of PMI, GME, and GGP and the low expression level of AAO contributed to the high AsA accumulation in non-heading Chinese cabbage.

Glutamate dehydrogenase isoenzyme 3 (GDH3) of Arabidopsis thaliana is regulated by a combined effect of nitrogen and cytokinin

In higher plants, NAD(H)-glutamate dehydrogenase (GDH; EC 1.4.1.2) is an abundant enzyme that exists in different isoenzymic forms. In Arabidopsis thaliana, three genes (Gdh1, Gdh2 and Gdh3) encode three different GDH subunits (β, α and γ) that randomly associate to form a complex array of homo- and heterohexamers. The modification of the GDH isoenzyme pattern and its regulation was studied during the development of A. thaliana in the gdh1, gdh2 single mutants and the gdh1-2 double mutant, with particular emphasis on GDH3. Investigations showed that the GDH3 isoenzyme could not be detected in closely related Arabidopsis species. The induction and regulation of GDH3 activity in the leaves and roots was investigated following nitrogen deprivation in the presence or absence of sucrose or kinetin. These experiments indicate that GDH3 is likely to play an important role during senescence and nutrient remobilization.

Stereoselective synthesis of (R)-phenylephrine using recombinant Escherichia coli cells expressing a novel short-chain dehydrogenase/reductase gene from Serratia marcescens BCRC 10948

(R)-Phenylephrine [(R)-PE] is an α1-adrenergic receptor agonist and is widely used as a nasal decongestant to treat the common cold without the side effects of other ephedrine adrenergic drugs. We identified a short-chain dehydrogenase/reductase (SM_SDR) from Serratia marcescens BCRC 10948 that was able to convert 1-(3-hydroxyphenyl)-2-(methylamino) ethanone (HPMAE) into (R)-PE. The SM_SDR used NADPH and NADH as cofactors with specific activities of 17.35±0.71 and 5.57±0.07mU/mg protein, respectively, at 30°C and pH 7.0, thereby indicating that this enzyme could be categorized as an NADPH-preferring short-chain dehydrogenase/reductase. Escherichia coli strain BL21 (DE3) expressing SM_SDR could convert HPMAE into (R)-PE with more than 99% enantiomeric excess. The productivity and conversion yield were 0.57mmolPE/lh and 51.06%, respectively, using 10mM HPMAE. Fructose was the most effective carbon source for the conversion of HPMAE to (R)-PE.

Oxidoreduction properties of bound ubiquinone in Complex I from Escherichia coli

The exploration of the redox chemistry of bound ubiquinone during catalysis is a prerequisite for the understanding of the mechanism by which Complex I (nicotinamide adenine dinucleotide (NADH):ubiquinone oxidoreductase) transduces redox energy into an electrochemical proton gradient. Studies of redox dependent changes in the spectrum of Complex I from Escherichia coli in the mid- and near-ultraviolet (UV) and visible areas were performed to identify the spectral contribution, and to determine the redox properties, of the tightly bound ubiquinone. A very low midpoint redox potential (<-300mV) was found for the bound ubiquinone, more than 400mV lower than when dissolved in a phospholipid membrane. This thermodynamic property of bound ubiquinone has important implications for the mechanism by which Complex I catalyzes proton translocation.

Diagnosis and management of Clostridium difficile infection

Clostridium difficile infection (CDI) is increasing in frequency and severity in and out of the hospital, with a high probability of recurrence after treatment. The recent literature on CDI was reviewed using PubMed to include recent publications dealing with diagnosis and therapy. Real-time polymerase chain reaction is a sensitive and useful diagnostic test for CDI but there are growing concerns of false-positive test results if the rate of CDI is low in the patient population providing samples and/or if the population being studied commonly includes people with C difficile colonization. Recommended therapy of CDI includes oral metronidazole for milder cases of CDI and oral vancomycin or fidaxomicin for more severe cases, each given for 10 days. Colectomy is being performed more frequently in patients with fulminant CDI. For treatment of first recurrences the drug used in the first bout can be used again and for second recurrences longer courses of vancomycin often are given in a tapered dose or intermittently to allow gut flora reconstitution, or other treatments including fidaxomicin may be used. Bacteriotherapy with fecal transplantation is playing an increasing role in therapy of recurrent cases. Metagenomic studies of patients with CDI during successful therapy are needed to determine how best to protect the flora from assaults from antibacterial drugs and to develop optimal therapeutic approaches. Immunotherapy and immunoprophylaxis offer opportunities to prevent CDI, to speed up recovery from CDI, and to eliminate recurrent infection. Humanized monoclonal antitoxin antibodies and active immunization with vaccines against C difficile or its toxins are both in development and appear to be of potential value.

Hydrogen peroxide stress provokes a metabolic reprogramming in Pseudomonas fluorescens: enhanced production of pyruvate

Pseudomonas fluorescens invoked a metabolic reconfiguration that resulted in enhanced production of pyruvate under the challenge of hydrogen peroxide (H₂O₂). Although this stress led to a sharp reduction in the activities of numerous tricarboxylic acid (TCA) cycle enzymes, there was a marked increase in the activities of catalase and various NADPH-generating enzymes to counter the oxidative burden. The upregulation of phosphoenolpyruvate synthase (PEPS) and pyruvate kinase (PK) coupled with the reduction of pyruvate dehydrogenase (PDH) in the H₂O₂-challenged cells appear to be important contributors to the elevated levels of pyruvate found in these bacteria. Increased pyruvate synthesis was evident in the presence of a variety of carbon sources including d-glucose. Intact cells rapidly consumed d-glucose with the concomitant formation of this monocarboxylic acid. At least a 12-fold increase in pyruvate production within 1h was observed in the stressed cells. These findings may be exploited in the development of technologies aimed at the conversion of carbohydrates into pyruvate.

Chicken liver glutamate dehydrogenase (GDH) demonstrates a histone H3 specific protease (H3ase) activity in vitro

Site-specific proteolysis of the N or C-terminus of histone tails has emerged as a novel form of irreversible post-translational modifications assigned to histones. Though there are many reports describing histone specific proteolysis, there are very few studies on purification of a histone specific protease. Here, we demonstrate a histone H3 specific protease (H3ase) activity in chicken liver nuclear extract. H3ase was purified to homogeneity and identified as glutamate dehydrogenase (GDH) by sequencing. A series of biochemical experiments further confirmed that the H3ase activity was due to GDH. The H3ase clipped histone H3 products were sequenced by N-terminal sequencing and the precise clipping sites of H3ase were mapped. H3ase activity was only specific to chicken liver as it was not demonstrated in other tissues like heart, muscle and brain of chicken. We assign a novel serine like protease activity to GDH which is specific to histone H3.

Fas receptor-deficient lpr mice are protected against acetaminophen hepatotoxicity due to higher glutathione synthesis and enhanced detoxification of oxidant stress

Acetaminophen (APAP) overdose is a classical model of hepatocellular necrosis; however, the involvement of the Fas receptor in the pathophysiology remains controversial. Fas receptor-deficient (lpr) and C57BL/6 mice were treated with APAP to compare the mechanisms of hepatotoxicity. Lpr mice were partially protected against APAP hepatotoxicity as indicated by reduced plasma ALT and GDH levels and liver necrosis. Hepatic Cyp2e1 protein, adduct formation and hepatic glutathione (GSH) depletion were similar, demonstrating equivalent reactive metabolite generation. There was no difference in cytokine formation or hepatic neutrophil recruitment. Interestingly, hepatic GSH recovered faster in lpr mice than in wild type animals resulting in enhanced detoxification of reactive oxygen species. Driving the increased GSH levels, mRNA induction and protein expression of glutamate-cysteine ligase (gclc) were higher in lpr mice. Inducible nitric oxide synthase (iNOS) mRNA and protein levels at 6h were significantly lower in lpr mice, which correlated with reduced nitrotyrosine staining. Heat shock protein 70 (Hsp70) mRNA levels were substantially higher in lpr mice after APAP.

CONCLUSION

Our data suggest that the faster recovery of hepatic GSH levels during oxidant stress and peroxynitrite formation, reduced iNOS expression and enhanced induction of Hsp70 attenuated the susceptibility to APAP-induced cell death in lpr mice.

Diagnostic algorithm using a sensitive broth culture method for detection of Clostridium difficile toxin from stool samples

BACKGROUND

The two-step glutamate dehydrogenase antigencytotoxicity neutralization assay algorithm has been found to be reliable for the diagnosis of toxigenic Clostridium difficile. However, the high sensitivity of the screening method is compromised by the relative low sensitivity of the second step, the direct cytotoxin neutralization assay (DCNA) using a fecal filtrate. The objective of the present study was to compare the DCNA with an indirect cytotoxin neutralization assay (ICNA).

METHODS

For ICNA, the cytotoxin B of C difficile was obtained from a broth culture of the stools and neutralized according to a standard cytotoxin assay using MRC-5 fibroblast cells.

RESULTS

A total of 923 stool specimens from adults were tested during a three-month period from June to August 2008. The prevalence of toxigenic C difficile was 13.5%. The sensitivity of the two-step algorithm was 88%. With the ICNA, 12% toxigenic C difficile were detected that were missed by DCNA.

CONCLUSIONS

The use of broth for the ICNA is convenient, and results in increased sensitivity of detection of toxigenic C difficile. It can be implemented in routine diagnosis.