Increase In Glutamate Dehydrogenase Activity Research Articles

Changes in growth, ammonium assimilation and amino acid levels in leaves of Arabidopsis thaliana under cadmium treatment

Cadmium is the most harmful soil pollutant due to its long biological half-life. In the present study, the effect of Cd on ammonium assimilation in Arabidopsis thaliana wild-type Col0 was investigated. Thirty-day-old Arabidopsis seedlings were exposed to 20 µM CdCl2 during different exposure times (0, 1, 2, 3, and 7 days). Seedling growth decreased under Cd stress mainly after 7 days of Cd exposure. Cd stress caused a gradual decrease in soluble leaf protein and induced an increase in leaf ammonium and the content of free amino acids such as glutamine (Gln), glutamate (Glu), asparagine (Asn), and proline (Pro), which may be related to the increase in protease activity. The results showed that the activities of Glutamine Synthetase (GS) and glutamate dehydrogenase (GDH) were inversely related. Cd stress led to an increase in GDH activity, whereas GS activity decreased. GDH activity on polyacrylamide gels showed that Cd induced both β- and α-enriched isoforms. Therefore, this study confirms that the ammonium assimilation process plays an important role for plants in adapting to Cd stress.

Assessment of serum glutamate dehydrogenase activity and comparison to serum alanine aminotransferase activity in cats with increased blood total T4 concentration.

Glutamate dehydrogenase (GLDH), a key enzyme in amino acid oxidation and urea production, is mainly derived from the liver and its activity may increase with hepatocellular necrosis. Feline hyperthyroidism is associated with elevated serum activities of various enzymes, but the pattern of serum GLDH activity has not been reported, to our knowledge. Feline clinical biochemistry results from 2 commercial diagnostic laboratories were reviewed retrospectively to assess changes in serum GLDH activity in cats with significantly elevated serum total T4 concentrations, which is highly suggestive of hyperthyroidism. A total of 2,773 records were analyzed, of which 2,370 (85%) had normal total T4 (≤50 nmol/L) and 403 (15%) had increased total T4 (≥60 nmol/L) concentrations. Among cats with an increased total T4 concentration, 26.5% had increased serum GLDH activity. All cats with increased GLDH activity also had increased serum ALT activity. In 42.9% of cats, ALT activity was increased, but GLDH activity was normal. In 30.5% of cats, both serum GLDH and ALT activities were within RIs. The fold-increase of GLDH activity was almost half of the ALT fold-increase. Although serum GLDH activity increased in some cats with hyperthyroidism, serum ALT activity increased more frequently and to a greater extent.

Adverse effects of polystyrene nanoplastic and its binary mixtures with nonylphenol on zebrafish nervous system: From oxidative stress to impaired neurotransmitter system

Micro(nano)plastics generally co-exist with other chemicals in the environment, resulting in inevitable interaction and combined toxic effects on biota. Nevertheless, little is known regarding the interaction of nanoplastics (NPs) with other co-occurring insults. Hereby, we investigated single and combined effects of chronic exposure (45 days) to polystyrene nanoplastic particulates (PS-NPs) and nonylphenol (4-NP) on zebrafish nervous system. Multiple biomarkers concerning with oxidative-stress [catalase (CAT) activity and reduced glutathione (GSH) level], cholinergic system [Acetylcholinesterase (AchE) activity], glutamatergic system [glutamine synthetase (GS) and glutamate dehydrogenase (GDH) activities], energy metabolism [a-ketoglutarate dehydrogenase (a-KGDH) activity], and histological alterations were assessed. Both single and binary exposure to PS-NPs and 4-NP induced oxidative stress through reducing CAT activity and GSH level, in which a more sever effect was noticed in combined exposure. The AchE activity was significantly inhibited only in single treatment groups demonstrating antagonistic interaction between PS-NPs and 4-NP. Effects on GS activity was also alleviated in binary exposure as compared with single exposure to each contaminant. In addition, an increase in GDH activity was noticed in PS-NPs at 10 and 100 μg/L, and simultaneous presence of PS-NPs and 4-NP with a greater response were observed in combined treatments. PS-NPs and 4-NP either in separate or binary mixtures disrupted energy metabolism by deficiency of α-KGDH activity; however, co-exposure to PS-NPs and 4-NP induced more intense adverse impacts on this parameter. Furthermore, histological analysis revealed that 4-NP and PS-NPs, alone or in combination, reduced neural cells. These findings provide new insight into the neurotoxic effects of binary exposure to PS-NPs and 4-NP at environmentally relevant concentrations. Overall, our findings raise concerns about the presence and toxicity of nano-scale plastic particulates and highlight the importance of investigating the interaction of Micro(nano)plastics with other environmental irritants.

Nitrogen form differently modulates growth, metabolite profile, and antioxidant and nitrogen metabolism activities in roots of Spartina alterniflora in response to increasing salinity

Sodium tolerance and nitrogen-source preferences are two of the most fascinating and ecologically important areas in plant physiology. Spartina alterniflora is a highly salt-tolerant species and appears to prefer ammonium (NH4+) over nitrate (NO3−) as an inorganic N source, presenting a suite of aboveground physiological and biochemical mechanisms that allows growth in saline environments. Here, we tested the interactive effects of salinity (0, 200, 500 mM NaCl) and nitrogen source (NO3−, NH4+, NH4NO3) on some physiological and biochemical parameters of S. alterniflora at the root level. After three months of treatments, plants were harvested to determine root growth parameters and total amino acids, proline, total soluble sugars, sucrose, and root enzyme activity. The control (0 mM NaCl) had the highest root growth rate in the medium containing only ammonium and the lowest in the medium containing only nitrate. Except for NO3−-fed plants, the 200 mM NaCl treatment generally had less root growth than the control. Under high salinity, NH4+-fed plants had better root growth than NO3−-fed plants. In the absence of salinity, NH4+-fed plants had higher superoxide dismutase, ascorbate peroxidase, glutathione reductase, and guaiacol peroxidase activities than NO3−-fed plants. Salinity generally promoted the activity of the principal antioxidant enzymes, more so in NH4+-fed plants. Nitrogen metabolism was characterized by higher constitutive levels of glutamate dehydrogenase (GDH) activity under ammonia nutrition, accompanied by elevated total amino acids levels in roots. The advantage of ammonium nutrition for S. alterniflora under salinity was connected to high amino acid accumulation and antioxidant enzyme activities, together with low H2O2 concentration and increased GDH activity. Ammonium improved root performance of S. alterniflora, especially under saline conditions, and may improve root antioxidant capacity and N-assimilating enzyme activities, and adjust osmotically to salinity by accumulating amino acids.

Salt Stress Induces Differentiated Nitrogen Uptake and Antioxidant Responses in Two Contrasting Barley Landraces from MENA Region

The interaction between salinity and nitrogen metabolism has been investigated in two barley landraces, one tolerant (“100/1B”) and one susceptible to salinity (“Barley medenine”) from the Middle East and North Africa (MENA) region. Barley plants were exposed to 50 mM NaCl for 7 days; then, salinity was increased to 150 mM NaCl in the presence (10 mM) or limitation (1 mM) of ammonium as a nitrogen source. Upon salinity, “100/1B” was shown to support N assimilation by enhancing the glutamine synthetase (GS) and glutamine oxoglutarate aminotransferase (GOGAT) cycle under high N, and the stimulation of the glutamate dehydrogenase (GDH) pathway under low N treatment. In “Barley medenine”, salinity reduced the GS/GOGAT cycle, and increased GDH activity. Upon salinity, Heat Shock Proteins 70 and PEPC remained unchanged in “100/1B”, while they decreased in “Barley medenine”. The tolerance degree is a determining factor in enzymes’ occurrence and regulation: exposed to salinity, “100/1B” rapidly increased APX and PEPC activities, while this was delayed in “Barley medenine”. Salinity increased cyt-G6PDH levels in “100/1B”, while “Barley medenine” showed a decrease in G6PDH isoforms. Correlation analyses confirm GOGAT was related to G6PDH; GDH and APX with PEPC in “100/1B” under moderate salinity; severe salinity correlated GDH with G6PDH and PEPC. In “Barley medenine” under salinity, GOGAT was correlated with G6PDH, while APX showed a relation with PEPC. Therefore, specific enzymatic activities and occurrence can be used to determine stress responsiveness of different landraces. We suggest that the rapid increase in G6PDH, APX, and nitrogen assimilation enzymes activities represents an index of tolerance in “100/1B” and a stress symptom in “Barley medenine”.

Rescue of myocardial energetic dysfunction in diabetes through the correction of mitochondrial hyperacetylation by honokiol.

Cardiac energetic dysfunction has been reported in patients with type 2 diabetes (T2D) and is an independent predictor of mortality. Identification of the mechanisms driving mitochondrial dysfunction, and therapeutic strategies to rescue these modifications, will improve myocardial energetics in T2D. We demonstrate using 31P-magnetic resonance spectroscopy (31P-MRS) that decreased cardiac ATP and phosphocreatine (PCr) concentrations occurred before contractile dysfunction or a reduction in PCr/ATP ratio in T2D. Real-time mitochondrial ATP synthesis rates and state 3 respiration rates were similarly depressed in T2D, implicating dysfunctional mitochondrial energy production. Driving this energetic dysfunction in T2D was an increase in mitochondrial protein acetylation, and increased ex vivo acetylation was shown to proportionally decrease mitochondrial respiration rates. Treating T2D rats in vivo with the mitochondrial deacetylase SIRT3 activator honokiol reversed the hyperacetylation of mitochondrial proteins and restored mitochondrial respiration rates to control levels. Using 13C-hyperpolarized MRS, respiration with different substrates, and enzyme assays, we localized this improvement to increased glutamate dehydrogenase activity. Finally, honokiol treatment increased ATP and PCr concentrations and increased total ATP synthesis flux in the T2D heart. In conclusion, hyperacetylation drives energetic dysfunction in T2D, and reversing acetylation with the SIRT3 activator honokiol rescued myocardial and mitochondrial energetics in T2D.

RETRACTED: L-leucine stimulates glutamate dehydrogenase activity and glutamate synthesis by regulating mTORC1/SIRT4 pathway in pig liver

The liver is the most essential organ for the metabolism of ammonia, in where most of ammonia is removed by urea and glutamine synthesis. Regulated by leucine, glutamate dehydrogenase (GDH) catalyzes the reversible inter-conversion of glutamate to ammonia. To determine the mechanism of leucine regulating GDH, pigs weighing 20 ± 1 kg were infused for 80 min with ammonium chloride or alanine in the presence or absence of leucine. Primary pig hepatocytes were incubated with or without leucine. In the in vivo experiments with either ammonium or alanine as the nitrogen source, addition of leucine significantly inhibited ureagenesis and promoted the production of glutamate and glutamine in the perfused pig liver (P < 0.05). Similarly, leucine stimulated GDH activity and inhibited sirtuin4 (SIRT4) gene expression (P < 0.01). Leucine could also activate mammalian target of rapamycin complex 1 (mTORC1) signaling (P < 0.05), as evidenced by the increased phosphorylation levels of ribosomal protein S6 kinase 1 (S6K1) and ribosomal protein S6 (S6). Interestingly, the leucine-induced mTORC1 pathway activation suitably correlated with increased GDH activity and decreased expression of SIRT4. Similar results were observed in primary cultured hepatocytes. Notably, leucine exerted no significant change in GDH activity in SIRT4-deficient hepatocytes (P > 0.05), while mTORC1 signaling was activated. Leucine exerted no significant changes in both GDH activity and SIRT4 gene expression in rapamycin treated hepatocytes (P > 0.05). In conclusion, L-leucine increases GDH activity and stimulates glutamate synthesis from different nitrogen sources by regulating mTORC1/SIRT4 pathway in the liver of pigs.

Downregulation of SIRT4 Expression Is Associated with Poor Prognosis in Esophageal Squamous Cell Carcinoma

Objective: SIRT4, a mitochondria-localized sirtuin, represses glutamine metabolism by inhibiting glutamate dehydrogenase (GDH). The current study aimed to evaluate the clinical and biological significance of SIRT4 in esophageal squamous cell carcinoma (ESCC). Methods: The study comprised 172 patients with surgically resected ESCC in two independent cohorts. SIRT4 mRNA expression was analyzed in Cohort 1 (n = 79) and SIRT4 protein expression in Cohort 2 (n = 93). The association of SIRT4 expression with clinicopathological parameters and prognosis was assessed. Furthermore, the biological role of SIRT4 in ESCC cell lines was examined. Results: SIRT4 expression was not correlated with any clinicopathological parameters in both cohorts. In Cohort 1, low-SIRT4-expression cases had poorer overall survival than high-SIRT4-expression cases (p = 0.016). In Cohort 2, SIRT4-negative cases had poorer overall survival and disease-free survival than SIRT4-positive cases (p = 0.011 and 0.0026). Multivariate analysis revealed that SIRT4 expression was an independent prognostic factor for overall survival (HR = 2.06, p = 0.038). The rate of distant recurrence was significantly higher in SIRT4-negative cases than in SIRT4-positive cases (39.4 vs. 7.4%; p = 0.0023). In vitro, SIRT4 knockdown significantly increased GDH activity and promoted cell proliferation and migration. Conclusion: SIRT4 is a potential prognostic biomarker in ESCC.

Utilizing camelid-derived single domain antibodies to enhance immunotherapy of ovarian cancer

growth, and cancer cells are well known to be “glutamine-addicted.” Glutamine is converted by glutaminase to glutamate, and glutamate is converted by glutamate dehydrogenase (GDH) to α-ketoglutarate, which enters the tricarboxylic acid cycle for the production of adenosine triphosphate (ATP). In addition, glutamine generates the antioxidant glutathione, which removes reactive oxygen species (ROS) and regulates critical cell signaling pathways. Our objective was to explore the effects of glutamine on ovarian cancer (OC) cell growth and metabolism. Methods: We used the OC cell lines HEY, SKOV3, and IGROV1 and assessed dell proliferation by MTT assay. Cell cycle progression and apoptosis were evaluated by Cellometer. Western immunoblotting was performed to evaluate the effects of glutamine on downstream targets of the mTOR and MAPK pathways and proteins related to cellular stress. Glucose uptake, GDH activity, lactate, ATP, and ROS production were all assessed by enzyme-linked immunosorbent assay. The effect of mTOR pathway inhibition on glutaminestimulated cell proliferation was assessed by 1) treatment with rapamycin, an mTOR inhibitor, and 2) knockdown of S6 by siRNA transfection. Results: Glutamine stimulated cell proliferation in a dose-dependent manner in the three OC cell lines. In addition, glutamine increased GDH activity, glucose uptake, and lactate and ATP production and resulted in increased phosphorylation of S6 and p42/44. As expected, glutamine starvation had the opposite effect on the OC cell lines, leading to inhibition of cell proliferation, induction of apoptosis and G1 cell cycle arrest, reduced glucose uptake, and decreased lactate and ATP production. Glutamine depletion also induced ROS production and increased expression of the cellular stress proteins PERK, PARP, Bip, and calnexin. Inhibition of S6 by siRNA or rapamycin resulted in inhibition of glutamine-induced cell proliferation as well as a decrease in GDH activity. Conclusions: Glutamine potently increased cell proliferation, glucose uptake, and ATP production whereas glutamine depletion had the opposite effects on OC cells. Glutamine-induced cell proliferation appeared dependent on the mTOR pathway. These studies suggest that targeting glutamine may be a promising therapeutic strategy for ovarian cancer.

Diets supplemented with glutamate or glutamine improve protein retention and modulate gene expression of key enzymes of hepatic metabolism in gilthead seabream (Sparus aurata) juveniles

Abstract The present study evaluates the effect of dietary glutamate and glutamine supplementation on growth performance, body composition and expression of key enzymes involved in the hepatic metabolism of juvenile gilthead seabream ( Sparus aurata ). Fish were fed for 52 days with four diets, which were identical in composition except for a 4% supplementation with glutamate (GLU diet), glutamine (GLN diet), carbohydrate (CHO diet) or bovine serum albumin (BSA diet). Glutamate and glutamine supplementation improved feed conversion ratio and protein retention compared to carbohydrate supplementation, and, in the case of glutamate, protein retention was improved over that of fish fed the protein supplemented diet. Feeding CHO and GLU diets resulted in up-regulation of glucokinase and lipogenic enzymes compared to fish fed GLN and BSA diets. Consistently, fish fed CHO or GLU diets showed higher triglyceride levels in serum and liver, and feeding the GLU diet resulted in higher body fat content than in fish fed GLN or BSA diets. The liver of fish fed GLN or BSA diets showed increased glutamate dehydrogenase activity in the direction of the glutamate oxidation. In contrast to fish fed the BSA diet, increased glutamate oxidation did not reduce free glutamine and glutamate levels in the liver of fish fed the GLN diet, suggesting that glutamine intake exceeded liver's energy requirements. In conclusion, glutamate supplementation improved hepatic glucose metabolism, whereas supplemented glutamine seems to be preferentially oxidized over amino acids derived from dietary protein, thus promoting higher protein retention in both cases. Our findings indicate that glutamate and glutamine could partly replace dietary protein and that glutamate supplementation could also facilitate protein replacement by carbohydrates in fish feeds.

Silicon improves salinity tolerance and affects ammonia assimilation in maize roots

AbstractThe present study was conducted to evaluate the effect of different salt concentrations (50 and 200 mM NaCl) on growth, permeability properties (electrolyte leakage, cell viability) and activity of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in roots of maize seedlings. Both salt concentrations significantly affected growth and permeability properties of maize seedling roots and this negative effect increased with concentration of salt and duration of experiments. On the other hand salinity induced only small changes in the activities of GS and GDH, usually small increase in the activity was observed. To characterise the possible protective effect of silicon (Si) on maize roots exposed to saline stress, different concentrations of Si were simultaneously applied to both, low (50 mM) and high (200 mM) salt concentrations. Possible protective effects of Si on studied parameters were analysed in time range of 3 days treatment with the most positive effect on salt-induced root growth inhibition at high salt concentration and electrolyte leakage. The results show significant increase in GDH activity under all the tested conditions, although the mechanisms underlying this increase have not been elucidated. The results indicate that silicon may ameliorate the salt-induced root growth inhibition and increase the plant vigour at stressful conditions.

Effect of Nitrogen and Sulphur Nutrition on Nitrogen assimilating Enzymes in Soybean Roots and Nodules

Soybean is an important legume crop with high protein content but deficient in sulphur (S) containing amino acids viz methionine and cysteine. Soybean protein quality can be improved by nutrient fertilization. Present studies report the effect of nitrogen (N) and S nutrition on nodulation, activities of ammonia assimilating enzymes and biochemical parameters in soybean roots and nodules. Nitrogen as urea @ 31.25 kg ha−1 and sulphur as gypsum @ 20 kg ha−1 alone significantly increased nodule number, fresh and dry weight per nodule, root length and nodular leghemoglobin content whereas total soluble proteins, free amino acids, glucose and sucrose content did not vary significantly in nodules and roots. Treatment of N or S significantly increased glutamate dehydrogenase activity in cytosol and bacteroidal fractions from 70 to 90 days after sowing whereas aspartate aminotransferase, glutamate synthase, glutamine synthetase and alanine aminotransferase activities showed non-significant variations in roots at different stages of development under the influence of N or S alone or their combination. Results suggested that N and S could improve nodulation and vegetative growth in soybean but ammonia assimilating enzyme activities in roots/nodules did not vary significantly.

An in vitro analysis of intestinal ammonia handling in fasted and fed freshwater rainbow trout (Oncorhynchus mykiss)

Ammonia transport and metabolism were investigated in the intestinal tract of freshwater rainbow trout which had been either fasted for 7 days, or fasted then fed a satiating meal of commercial trout pellets. In vivo, total ammonia concentrations (T amm) in the chyme were approximately 1 mmol L(-1) across the entire intestine at 24 h after the meal. Highest chyme pH and P NH3 values occurred in the posterior intestine. In vitro gut sac experiments examined ammonia handling with mucosal (Jmamm) and serosal (Js amm) fluxes under conditions of fasting and feeding, with either background (control ≤ 0.013 mmol L(-1)) or high luminal ammonia concentrations (HLA = 1 mmol L(-1)), the latter mimicking those seen in chyme in vivo. Feeding status (fasted or fed) appeared to influence ammonia handling by each individual section. The anterior intestine exhibited the greatest Jm amm and Js amm values under fasted control conditions, but these differences tended to disappear under typical post-feeding conditions when total endogenous ammonia production (Jt amm = Js amm - Jm amm, signs considered) was greatly elevated in all intestinal sections. Under fasted conditions, glutamate dehydrogenase (GDH) and glutaminase (GLN) activities were equal across all sections, but the ammonia-trapping enzyme glutamine synthetase (GS) exhibited highest activity in the posterior intestine, in contradiction to previous literature. Feeding clearly stimulated the total rate of endogenous ammonia production (Jt amm), even in the absence of a high luminal ammonia load. This was accompanied by an increase in GDH activity of the anterior intestine, which was also the site of the largest Jt amm. In all sections, during HLA exposure, either alone or in combination with feeding, there were much larger increases in endogenous Jt amm, most of which was effluxed to the serosal solution. This is interpreted as a response to avoid potential cytotoxicity due to overburdened detoxification mechanisms in the face of elevated mucosal ammonia. Thus T amm of the intestinal tissue remained relatively constant regardless of feeding status and exposure to HLA. Ammonia production by the gut may explain up to 18 % of whole-body ammonia excretion in vivo under fasting conditions, and 47 % after feeding, of which more than half originates from endogenous production rather than from absorption from the lumen.

Ammonia-related metabolism of tobacco varieties differing in their susceptibility to Alternaria alternata

Some studies report that ammonia is an important factor of disease development in tobacco plants and various post-harvest fruits. Four tobacco (Nicotiana tabacum L.) varieties resistant or susceptible to Alternaria alternata (Fries) Keissler, a tobacco pathogenic fungus, were used to investigate whether there are differences in ammonia accumulation and the related metabolism of senescing leaves. The results showed that: (a) the leaves of susceptible varieties had significantly higher apoplastic [NH4+], pH, and ammonia emission potential (Γ-values) than resistant varieties during the period from 40 to 60 days of leaf age; (b) leaf tissue [NH4+] and total N concentrations in the tobacco varieties were not in line with their susceptibility or resistance to disease; (c) the increases in the apoplastic pH, Γ-values, and leaf [NH4+] occurred in parallel with a significant decline in glutamine synthetase activity. Compared with the resistant varieties, apoplastic pH values and Γ values were increased more rapidly in the susceptible varieties due to a steeper decline in glutamine synthetase activity and a slower increase in glutamate dehydrogenase activity. In conclusion, NH3 accumulation or NH3-dependent alkalinization rather than [NH4+] and total N appears to be mainly attributed to the enhanced susceptibility of tobacco plants to A. alternata.

Two genetic forms of hyperinsulinemic hypoglycemia caused by dysregulation of glutamate dehydrogenase

Glutamate dehydrogenase (GDH) has recently been shown to be involved in two genetic disorders of hyperinsulinemic hypoglycemia in children. These include the hyperinsulinism/hyperammonemia syndrome caused by dominant activating mutations of GLUD1 which interfere with inhibitory regulation by GTP and hyperinsulinism due to recessive deficiency of short-chain 3-hydroxy-acyl-CoA dehydrogenase (SCHAD, encoded by HADH1). The clinical manifestations of the abnormalities in pancreatic ß-cell insulin regulation include fasting hypoglycemia, as well as protein-sensitive hypoglycemia. The latter is due to abnormally increased sensitivity of affected children to stimulation of insulin secretion by the amino acid, leucine. In patients with GDH activating mutations, mild hyperammonemia occurs in both the basal and protein-fed state, possibly due to increased renal ammoniagenesis. Some patients with GDH activating mutations appear to be at unusual risk of developmental delay and generalized epilepsy, perhaps reflecting consequences of increased GDH activity in the brain. Studies of these two disorders have been carried out in mouse models to define the mechanisms of insulin dysregulation. In SCHAD deficiency, the activation of GDH is due to loss of a direct inhibitory protein-protein interaction between SCHAD and GDH. These two novel human disorders demonstrate the important role of GDH in insulin regulation and illustrate unexpectedly important reasons for the unusually complex allosteric regulation of GDH.

Astrocytes and Epilepsy

Astrocytes form a significant constituent of seizure foci in the human brain. For a long time it was believed that astrocytes play a significant role in the causation of seizures. With the increase in our understanding of the unique biology of these cells, their precise role in seizure foci is receiving renewed attention. This article reviews the information now available on the role of astrocytes in the hippocampal seizure focus in patients with temporal lobe epilepsy with hippocampal sclerosis. Our intent is to try to integrate the available data. Astrocytes at seizure foci seem to not be a homogeneous population of cells, and in addition to typical glial fibrillary acidic protein, positive reactive astrocytes also include a population of neuron glia-2-like cells The astrocytes in sclerotic hippocampi differ from those in nonsclerotic hippocampi in their membrane physiology, having elevated Na+ channels and reduced inwardly rectifying potassium ion channels, and some having the capacity to generate action potentials. They also have reduced glutamine synthetase and increased glutamate dehydrogenase activity. The molecular interface between the astrocyte and microvasculature is also changed. The astrocytes are also associated with increased expression of many molecules normally concerned with immune and inflammatory functions. A speculative mechanism postulates that neuron glia-2-like cells may be involved in creating a high glutamate environment, whereas the function of more typical reactive astrocytes contribute to maintain high extracellular K+ levels; both factors contributing to the hyperexcitability of subicular neurons to generate epileptiform activity. The functions of the astrocyte vascular interface may be more critical to the processes involved in epileptogenesis.

The effects of L-DOPA on glutamate dehydrogenase activity in the cerebral neurons of rats with different motor activities

We studied the brains of stress-resistant Wistar rats and stress-prone August rats under normal conditions and after long-term L-DOPA administration. We performed a histochemical study of glutamate dehydrogenase (GDH) activity in layers III and V of the sensorimotor cortex, caudate nucleus, nucleus accumbens, and the CA3 field of the hippocampus. We did not find any differences in the GDH activity in the brain structures of the control Wistar and August rats with high or low levels of locomotion in the “open field” test. The activity of GDH was higher in layer V of the sensorimotor cortex and the caudate nucleus and lower in the hippocampus of August rats with low levels of locomotion as compared to Wistar rats with high locomotor activity. Administration of L-DOPA resulted in an increase in GDH activity in the sensorimotor cortex, caudate nucleus, and nucleus accumbens in Wistar rats with high levels of locomotion in the “open field” test. In Wistar rats with low locomotor activity, L-DOPA activated GDH in the hippocampus and decreased its concentration in the caudate nucleus and nucleus accumbens. In August rats with low levels of locomotion, L-DOPA increased GDH activity in the caudate nucleus and nucleus accumbens and decreased it in layer V of the sensorimotor cortex. The local specificity of GDH activity in the rat brain under normal conditions and during dopaminergic system hyperfunction are discussed.

Intestinal osmoregulatory acclimation and nitrogen metabolism in juveniles of the freshwater marble goby exposed to seawater

The objective of this study was to elucidate the role of the intestine from juveniles of the marble goby, Oxyeleotris marmorata, during seawater (SW) exposure. It has been reported elsewhere that SW-exposed juvenile O. marmorata exhibits hypoosmotic and hypoionic regulation, with the induction of branchial Na(+)/K(+)-ATPase (NKA), Na(+):K(+):2Cl(-) cotransporter (NKCC), and cystic fibrosis transmembrane receptor-like chloride channels. Here, we report that SW exposure also led to significant increases in the activity and protein abundance of NKA in, and probably an increase in Na(+) uptake through, its intestine. Additionally, there was an increase in apical NKCC immunoreactivity in the intestinal epithelium, indicating that there could be increased Cl(-) uptake through the intestine. These results suggest that absorption of ions, and hence water, from the intestinal lumen could be an essential part of the osmoregulatory process in juvenile O. marmorata during exposure to SW. Furthermore, there were significant increases in the glutamate content, and the aminating activity and protein abundance of glutamate dehydrogenase (GDH) in the intestine of fish exposed to SW. Since the intestinal glutamine synthetase activity and protein abundance decreased significantly, and the intestinal glutamine content remained unchanged, in the SW-exposed fish, excess glutamate formed via increased GDH activity in the intestine could be channeled to other organs to facilitate the increased synthesis of amino acids. Taken together, our results indicate for the first time that, besides absorbing ions and water during SW exposure, the intestine of juvenile O. marmorata also participated in altered nitrogen metabolism in response to salinity changes.

Glioblastoma Cells Require Glutamate Dehydrogenase to Survive Impairments of Glucose Metabolism or Akt Signaling

Oncogenes influence nutrient metabolism and nutrient dependence. The oncogene c-Myc stimulates glutamine metabolism and renders cells dependent on glutamine to sustain viability ("glutamine addiction"), suggesting that treatments targeting glutamine metabolism might selectively kill c-Myc-transformed tumor cells. However, many current or proposed cancer therapies interfere with the metabolism of glucose, not glutamine. Here, we studied how c-Myc-transformed cells maintained viability when glucose metabolism was impaired. In SF188 glioblastoma cells, glucose deprivation did not affect net glutamine utilization but elicited a switch in the pathways used to deliver glutamine carbon to the tricarboxylic acid cycle, with a large increase in the activity of glutamate dehydrogenase (GDH). The effect on GDH resulted from the loss of glycolysis because it could be mimicked with the glycolytic inhibitor 2-deoxyglucose and reversed with a pyruvate analogue. Furthermore, inhibition of Akt signaling, which facilitates glycolysis, increased GDH activity whereas overexpression of Akt suppressed it, suggesting that Akt indirectly regulates GDH through its effects on glucose metabolism. Suppression of GDH activity with RNA interference or an inhibitor showed that the enzyme is dispensable in cells able to metabolize glucose but is required for cells to survive impairments of glycolysis brought about by glucose deprivation, 2-deoxyglucose, or Akt inhibition. Thus, inhibition of GDH converted these glutamine-addicted cells to glucose-addicted cells. The findings emphasize the integration of glucose metabolism, glutamine metabolism, and oncogenic signaling in glioblastoma cells and suggest that exploiting compensatory pathways of glutamine metabolism can improve the efficacy of cancer treatments that impair glucose utilization.

Glutamate dehydrogenase activity in lymphocytes of B-cell chronic lymphocytic leukaemia patients

Objectives: To investigate the pattern of glutamate dehydrogenase (GLDH) activity, GLUD1 and GLUD2 expressions in peripheral blood mononuclear cells (PBMC) of untreated B-chronic lymphocytic leukemia (B-CLL) in healthy individuals (HI) and patients with infectious mononucleosis (IM). Design and methods: GLDH activity was determined in a supernatant obtained from pelleted PBMC. GLUD1 and GLUD2 mRNA expression was determined using a quantitative real-time polymerase chain reaction. CD19 + B cells from PBMC were purified by using positive selection. Results: The highest GLDH activity was found in PBMC of the B-CLL group followed by the HI group and IM group. The PBMC GLDH activity was higher in 60% of the B-CLL patients according to the established reference interval for our HI (2.17–5.70 μkat/g protein). The greater GLDH activity was also found in the CD19 + cell preparation of the B-CLL patients (two of the three) but not in HI ( n = 3). The median value of GLUD1 expression was highest in the IM group ( n = 11), followed by the HI ( n = 14) and B-CLL groups ( n = 59) (median 4.69/3.78, P < 0.005 and 4.69/2.91, P < 0.0005, respectively). GLUD2 expression was not significantly different between groups. Conclusions: The increased GLDH activity is specific for the PBMC of B-CLL patients. The GLUD1 but not the GLUD2 gene expression pattern is different between the PBMC of IM and B-CLL patients.