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PubMed2005

Contribution of extracellular glutamine as an anaplerotic substrate to neuronal metabolism: a re-evaluation by multinuclear NMR spectroscopy in primary cultured neurons.

Multinuclear NMR spectroscopy is used to investigate the effect of glutamine on neuronal glucose metabolism. Primary neurons were incubated with [1-(13C)]glucose in the absence or presence of glutamine (2 mM) and/or NH4Cl (5 mM). After ammonia-treatment, the concentrations of high-energy phosphates decreased up to 84% of control, which was aggravated in glutamine-containing medium (up to 42% of control). These effects could not be attributed to changes in mitochondrial glucose oxidation. Withdrawal of glutamine decreased amino acid concentrations, e.g. of glutamate to 53%, but also considerably lessened the 13C enrichment in [4-(13C)]glutamate to 8.3% of control, and decreased the 13C-enrichment in acetyl-CoA entering the Krebs cycle (P < 0.001). Thus, although glutamine is potent in replenishing neuronal glutamate stores, glutamate formation is mainly attributed to its de novo synthesis from glucose. Furthermore, mitochondrial glucose metabolism strongly depends on the supply of carbons from glutamine, indicating that exogenous glutamine is a well-suited substrate to replenish neuronal Krebs cycle intermediates.

Ammonium Chloride↗

PubMed1994

A cost-evaluation of glutamine-supplemented parenteral nutrition in adult bone marrow transplant patients.

OBJECTIVE: In a randomized, double-blind, prospective clinical trial, we evaluated the metabolic effects of glutamine-supplemented parenteral nutrition in patients with bone marrow transplants. We compared hospital charge and cost data for the two groups of patients in the trial. DESIGN: Retrospective review. SETTING: Bone Marrow Transplant Unit, Brigham and Women's Hospital, Boston, Mass. SUBJECTS: Forty-three patients admitted to the Bone Marrow Transplant Unit were assigned randomly to receive either standard parenteral nutrition or an isocaloric, isonitrogenous parenteral nutrition solution containing glutamine starting on day 1 after bone marrow transplant. The two groups were well matched for diagnosis, antineoplastic treatment, and sex. MEASURES: The primary clinical end points evaluated were nitrogen balance, length of hospitalization, incidence of infection, and results of microbial culture. After completion of the study, we compared the hospital charges for the categories of room and board, surgery, laboratory, pharmacy, radiology, ancillary, and miscellaneous between the two groups of patients. STATISTICAL ANALYSIS PERFORMED: The two groups were compared using the unpaired t test or Mann-Whitney test for nonparametric measurements. A P value of < .05 was considered significant. RESULTS: Nitrogen balance improved in the glutamine-supplemented group compared with control subjects (-1.4 +/- 0.5 g/day vs 4.2 +/- 1.2 g/day, respectively; P = .002). Length of hospitalization was significantly shorter in the glutamine-supplemented group than in the control group (29 +/- 1 day vs 36 +/- 2 days, respectively; P = .017). The incidence of positive microbial cultures and clinical infection was also significantly lower with glutamine supplementation. Hospital charges were $21,095 per patient less in the glutamine-supplemented group compared with charges for patients who received standard therapy. Room and board charges were significantly different: $51,484 +/- 2,647 for the glutamine-supplemented group vs $61,591 +/- 3,588 in the control group (P = .02). CONCLUSION: This intervention study using a new therapy demonstrated clinical and nutritional benefits to patients and cost savings to the hospital.

Adult↗

PubMed1987

Glutamine and glutamate: automated quantification and isotopic enrichments by gas chromatography/mass spectrometry.

A method is described for simultaneous quantification of glutamine and glutamate plasma levels and isotopic enrichments in these compounds. Glutamine and glutamate are analyzed intact as their tertiary-butyldimethylsilyl derivatives. Deuterated glutamine and glutamate are used as internal standards for quantification by reverse isotope dilution. Preparation of plasma samples is accomplished by adding ammonium formate as an ion-pairing agent followed by extraction of the amino acids into 4.3:1 methanol:water. Negligible amounts of glutamine to glutamate conversion are observed during the sample preparation and GC/MS analysis. Since glutamine is analyzed intact, both single and double [15N]glutamine labels can be quantified. [15N]Glutamine at 0.2 to 11 mol% excess was measured in plasma with an average relative standard error of 3.8%, and [15N]glutamate over a range of 0.4 to 9 mol% excess was measured with a mean relative standard error of 12%. At glutamate levels above 1 mol% excess 15N, the mean relative standard error was 6%. Finally, automated sample injection into the GC/MS and automated data reduction are used for the analysis of samples by GC/MS.

Animals↗

PubMed1986

The transport of glutamine into rat mesenteric lymphocytes.

The transport of glutamine into isolated rat mesenteric lymphocytes was studied. This transport appears to be dependent upon the Na+ gradient. The Km for glutamine transport was about 1.0 mM. A large number of amino acids were shown to inhibit the rate of transport of both serine and glutamine into lymphocytes. The transport of glutamine was competitively inhibited by serine and that for serine was similarly inhibited by glutamine. In contrast, histidine and 2-(methylamino)isobutyrate inhibited the transport of both serine and glutamine noncompetitively. It is concluded that glutamine is transported into rat mesenteric lymphocytes by a process similar to System ASC described for other cells.

Amino Acids↗

PubMed1979

Glutamate as a CNS transmitter. I. Evaluation of glucose and glutamine as precursors for the synthesis of preferentially released glutamate.

Slices of the molecular layer of the dentate gyrus of the hippocampal formation were incubated with either [14C]glucose, [14C]pyruvate or 14C glutamine and the efflux of endogenous and radioactive glutamate was monitored under various conditions. After prelabeling with either [14C]glutamine or [14C]glucose elevation of K+ concentration to 56 mM (Ca2+ free) increased efflux of endogenous and [14C]glutamate. Introduction of Ca2+ into the elevated K+ medium further increased the efflux of endogenous glutamate and radioactive glutamate derived from any of the precursors tested. In glutamine containing media, the increase in glutamate efflux as well as basal efflux was considerably higher than in the absence of glutamine and the specific activity of glutamate release was higher than that in tissue. Thus glutamine was superior to glucose or pyruvate as precursor and most specifically labeled the putative transmitter pool of glutamate. Similar experiments were carried out 4 and 14 days after a unilateral lesion in the entorhinal cortex which provides about 60% of the total synaptic input to the dentate granule cells. The Ca2+ dependent release of glutamate derived from either glucose or glutamine was markedly reduced on the operated side. This result suggests that the transmitter pool of glutamate is in perforant path terminals and can be synthesized from glucose or glutamine.

Animals↗

PubMed1982

Glutamine and glutamate transport in cultured neuronal and glial cells.

The uptake of L-glutamine in neuronal and glial cultures derived from rat cerebral hemispheres was found to be mediated by a low affinity-high capacity mechanism which was concentrative in both cell types; the calculated Km and Vmax were twice as high in glial than in neuronal cultures. In contrast L-glutamate was taken up by a high affinity system which was particularly efficient and concentrative in the glial cells. Different transport mechanisms for L-glutamine appeared to operate in the two cell types: L-glutamine uptake in neurons was sodium-dependent, specifically inhibited by L-glutamine but not affected by high potassium concentrations in the external medium; on the other hand, glial glutamine transport was decreased when potassium concentration increased, was sodium-independent and significantly inhibited by 3 structurally related amino acids. No significant contribution of homoexchange could be detected in either cell type. After [14C]glutamine preincubation, the radioactivity released into the superfusion medium by neuronal cells was increased in the presence of a high potassium concentration; no such effect could be seen in the case of glial cultures. A regulatory mechanism is suggested where astrocyte depolarization and repolarization would channel a flux of glutamine toward the neurons, subsequent to a glutamate flux in the opposite direction.

Animals↗

PubMed1982

Determination of [amide-15N]glutamine in plasma with gas chromatography-mass spectrometry.

A gas chromatographic-mass spectrometric method is described for determination of isotopic enrichment in [amide-15N]glutamine. The method involves the isolation of glutamine with an anionic exchange resin and the enzymatic hydrolysis of glutamine with glutaminase. The ammonia derived from the amide group is converted enzymatically to glutamic acid and isotopic enrichment in the latter compound is determined following formation of the N-TFA-glutaminate derivative. The method gave a linear result for [amide-15N]glutamine in the 0.5--21.5 atom % excess range with a mean coefficient of variance of 7.8%. Determination of plasma glutamine by isotope dilution showed a mean recovery of 94%. The appearance of plasma [amide-15N]glutamine was measured in a healthy adult following the intravenous administration of 15NH4Cl (350 mumol). A peak enrichment of 12 atom % excess was observed by 3.5 min.

Ammonia↗

PubMed1987

A positive relationship between protein synthetic rate and intracellular glutamine concentration in perfused rat skeletal muscle.

During muscle-protein wasting associated with injury and disease the distribution ratio of free glutamine between muscle and blood falls. In pursuing possible consequences of this, we investigated the relationship between the rate of muscle protein synthesis and intramuscular glutamine concentration, manipulated acutely in the isolated perfused rat hindquarter. Increasing perfusate glutamine from 0.67 to 5.0 mM caused a 200% increase in intracellular glutamine and a 66% increase in protein synthesis in the absence of insulin; in the presence of insulin a 30% increase in intramuscular glutamine was accompanied by an 80% increase in protein synthesis. Analysis of variance of the results confirmed the existence of positive relationships between intramuscular glutamine and protein synthesis in the presence or absence of insulin. Control of the size of the intramuscular free pool of glutamine may be important in determining the muscle protein mass.

Animals↗

PubMed1990

Effect of chemically induced diabetes mellitus on glutamine transport in rat intestine.

The effect of chemically induced diabetes mellitus on the intestinal transport of glutamine was examined using a brush-border membrane vesicle technique. Diabetes was induced by a single intraperitoneal injection of streptozotocin (100 mg/kg body weight). Control and diabetic rats were studied 5 days following the induction of diabetes. Na(+)-dependent and Na(+)-independent glutamine (0.5 mM) transport was found to be significantly higher in the diabetic rats than in the control rats. This increase was found to be caused by a significant increase in the Vmax of the Na(+)-dependent and the Na(+)-independent glutamine transport processes in the diabetic rats (Vmax of 3742 +/- 487 and 2055 +/- 279 pmol/mg protein per 7 s, respectively) compared with that of the control rats (2183 +/- 75 and 1271 +/- 83 pmol/mg protein per 7 s, respectively). The apparent Km values of glutamine transport systems, on the other hand, were similar in the two rat groups. Insulin treatment of the diabetic rats significantly reduced the Vmax of glutamine transport by both the Na(+)-dependent and the Na(+)-independent processes to a level similar to that of the control rats (Vmax in the insulin-treated diabetic rats of 2036 +/- 123 and 1247 +/- 105 pmol/mg protein per 7 s, respectively). This study demonstrates that chemically induced diabetes mellitus is associated with an increase in intestinal glutamine transport. This increase is the result of the diabetic condition itself and appears to be mediated through an increase in the number of the transport carriers of glutamine.

Animals↗

PubMed1989

Skeletal muscle glutamine metabolism during sepsis in the rat.

1. The effect of sepsis, induced by caecal ligation plus puncture (CLP) or endotoxin injection, on glutamine metabolism was studied in rat skeletal muscle. 2. The concentration of glutamine in muscle was decreased by CLP or after 24 or 48 hr after injection of endotoxin. However, the concentration was increased 3 hr after injection of endotoxin. 3. The plasma glutamine concentration was decreased by CLP, but it was unchanged after injection of endotoxin. 4. The rate of glutamine release from incubated stripped soleus muscles was increased in the muscles removed from animals subjected to CLP or from animals injected with endotoxin. 5. It is concluded that sepsis results in marked changes in skeletal muscle glutamine metabolism, which may be used as an early indicator of the septic state. During sepsis there is likely to be an increased demand for glutamine by the immune system, kidney and intestine. 6. This study provides evidence that during sepsis the rate of release of glutamine from the skeletal muscle per se is increased to a sufficient extent to satisfy this increased requirement.

Animals↗

PubMed1993

The concentrations of glutamine and ammonia in commercially available cell culture media.

The amino acid glutamine is an essential nutrient for cells in culture. In aqueous solutions such as liquid culture media, glutamine spontaneously decomposes into ammonia. In this study, we examined the toxicity of ammonia for two different cell lines. In mouse hybridoma cell cultures, viable cell counts were reduced at exogenous ammonia concentrations of 1000 microM. In the human promyelocytic cell line however, viable cell counts were shown to be reduced at exogenous ammonia concentrations of 300 microM. Next, we determined ammonia and glutamine levels in 11 commercially available media on the day of delivery. It was found that all media contained significantly less glutamine than prescribed. Ammonia was found in all media with concentrations ranging up to 1000 microM. Storage at both 4 degrees C and 20 degrees C caused a further degradation of glutamine and significant accumulation of ammonia in all media. The degradation curves of the various media were used to calculate the first order degradation constant k, which can be used to determine the kinetics of the spontaneous decomposition in culture media. These results suggest that precautions must be taken to avoid the deterioration of commercially available culture media, because of the decay of glutamine. Long storage times lead to a rapid decay of glutamine and an accumulation of the toxic degradation product ammonia.

Ammonia↗

PubMed1994

Glutamine protects Chinese hamster ovary cells from radiation killing.

Chinese Hamster Ovary (CHO) cells were propagated in vitro and exposed to varying doses of ionizing radiation. The surviving fraction of cells was determined, being found to be a function of the radiation dose. The cell survival curves obtained as a function of radiation dose were modified by the inclusion of varying doses of glutamine in the medium with glutamine demonstrating a radioprotective effect. The radioprotectant effect of glutamine for CHO cells was more pronounced at higher radiation doses. Glutamine has been categorized as a non-essential amino acid in that it can be synthesized in some tissues; however, a number of cell lines require glutamine to survive and grow in vitro and supplementation of glutamine has been found to ameliorate the stress of surgery or irradiation to the gastrointestinal tract. It may be appropriate to consider glutamine as a conditionally essential amino acid.

Animals↗

PubMed1988

Glutamine and glucose metabolism in human peripheral lymphocytes.

The metabolism of glutamine and glucose in resting and concanavalin A-stimulated human peripheral lymphocytes was investigated. Glutamine was metabolized at a high rate by resting and mitogen-stimulated human peripheral lymphocytes and the major end-products of glutamine metabolism were glutamate, aspartate, CO2, and ammonia: the carbon from glutamine may contribute about 21% to respiration. Concanavalin A enhanced the formation of all end-products except glutamate, indicating that more glutamine was metabolized beyond the stage of glutamate in the mitogen-stimulated cells. Mitogenic stimulation caused an increase in the rates of glucose utilization, lactate production and 14CO2 from variously labeled [14C] glucose. Concanavalin A caused an increase in the oxidation of pyruvate as indicated by the enhanced release of 14CO2 from [2-14C]-, [3,4-14C]-, and [6-14C]-glucose. When both glucose and glutamine were presented to the cells, the rates of utilization of both substrates increased and the increased rates of glucose and glutamine utilization could be accounted for mainly by increased rates of lactate and glutamate production, respectively.

Adult↗

PubMed1990

Splanchnic, renal, and muscle clearance of alanylglutamine in man and organ fluxes of alanine and glutamine when infused in free and peptide forms.

The present study was designed to investigate organ metabolism of intravenously (IV) infused (100 mumol.h-1.kg-1) alanylglutamine and its amino acid constituents in a group of healthy subjects. The dipeptide clearance (mumol/min) by kidney (51 +/- 3) was significantly (P less than .01) greater than the clearance by either splanchnic organs (19 +/- 6) or skeletal muscle (21 +/- 8). Infusion of alanylglutamine significantly (P less than .01) increased arterial plasma concentrations of free alanine (260 +/- 31 v 330 +/- 38 mumol/L) and free glutamine (620 +/- 66 v 764 +/- 65 mumol/L) when compared with the baseline period. Concurrently, splanchnic uptake of alanine and glutamine increased and muscle release of alanine ceased. However, muscle release of glutamine remained unaffected. Renal balances of alanine and glutamine changed from neutral to negative (net release) and from positive (net uptake) to neutral, respectively. Infusion of a corresponding mixture of alanine and glutamine had similar effects on arterial plasma concentrations and splanchnic and muscle balances of alanine and glutamine, but had no effect on renal balances of these amino acids. From these studies in man, we conclude that kidney predominates over other organs in clearance of alanylglutamine from plasma and that this may account for the different effect of infusion of alanine and glutamine in free and peptide forms on renal fluxes of these amino acids.

Adult↗

PubMed1992

Glutamine and macrophage function.

The effects of glutamine concentration on the phagocytosis of an opsonized antigen, the synthesis of RNA, and the production of interleukin-1 (IL-1) by macrophages were investigated in vitro. A minimum A minimum of 0.125 mmol/L glutamine was required for a significant increase in phagocytosis of opsonized sheep erythrocytes, compared with that recorded for macrophages cultured in the absence of glutamine. The synthesis of 3H-RNA by macrophages also required 0.125 mmol/L glutamine in the culture medium before it was significantly increased above the levels of control cultures. A minimum of 0.03 mmol/L glutamine was required for the induction of significant levels of IL-1 by lipopolysaccharide (LPS)-stimulated macrophages. Therefore, recent findings suggesting that decreases in plasma glutamine resulting from major burn injury, sepsis, trauma, and surgery may be partly responsible for the associated impairment of immune function now have a basis in both phagocytosis and in modulation of the synthesis of IL-1 (the first cytokine of the interleukin cascade that leads to specific immunity) by macrophages, in addition to the previously established dependency of lymphocytes on external sources of glutamine for their replication.

Analysis of Variance↗

PubMed1995

Influence of stage of lactation on glucose and glutamine metabolism in isolated enterocytes from dairy cattle.

Pathways of glutamine and glucose metabolism in early-, mid-, and late-lactation dairy cows were evaluated by in vitro incubations of enterocytes for 2 hours with [U-14-C]glutamine and [U-14C]glucose. Enterocytes from early-lactation cows produced greater amounts of CO2 from glutamine in concentrations that ranged from 2 to 8 mmol/L than enterocytes from either mid- or late-lactation cows. Enterocytes from early-lactation cows also produced greater amounts of CO2 from 4 and 6 mmol/L glucose than enterocytes from either mid- or late-lactation cows. Glutamine was metabolized via glutaminolysis mainly to ammonia, alanine, aspartate, glutamate, and CO2, and more of these products were produced in enterocytes from early-lactation cows than from pooled mid- and late-lactation (PML) cows. Glucose was metabolized mainly to lactate, as compared with pyruvate and CO2. Lactate and CO2 production were both greater in enterocytes from early-lactation cows than from PML cows. Glutamine as the sole substrate accounted for all the energy requirements of enterocytes from early-lactation cows but contributed only 31% in the presence of glucose. Similarly, glucose accounted for all the energy requirements of enterocytes from early-lactation cows and contributed 69% in the presence of glutamine. In enterocytes from all cows, the rate of adenosine triphosphate (ATP) production was greater in the presence of both glucose and glutamine compared with that in the presence of either substrate alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1990

The transport of L-glutamine into cultured human fibroblasts.

The transport of L-glutamine has been studied in diploid human fibroblasts in culture. Mathematical discrimination by nonlinear regression, competition analysis, and conditions varying the relative contribution of the various mediations have been used to characterize the systems engaged in the inward transport of this amino acid. The adopted criteria showed that L-glutamine enters the fibroblast by the Na(+)-dependent systems ASC and A and by a Na(+)-independent route identified as system L. The relative contribution of these agencies to the total saturable uptake of glutamine varied with the concentration of the amino acid and with the nutritional state of the cell. At amino acid concentrations approaching those encountered in human plasma: (1) system ASC represented the primary mediation for entry of L-glutamine in human fibroblasts; (2) the contribution of system A was lower, though significant, in unstarved repressed cells and became predominant in starved derepressed cells; (3) the Na(+)-dependent system L accounted for less than one-fifth of glutamine uptake in either nutritional condition. The changes in the relative contribution of the various systems to the uptake of glutamine as a function of its concentration may have implications in pathophysiology under conditions associated with enhanced glutamine concentrations in the extracellular fluids.

Amino Acids↗

PubMed1992

Characterization of glutamine metabolism in two related murine hybridomas.

Aspects of glutamine metabolism were examined in two related hybridomas, a high-producing line (PQX B1/2) and a low-producing line (PQX B2/2). The growth and metabolic characteristics of both cell lines were identical or very similar. During batch growth glutamine was completely exhausted from the medium and an examination of the fate of [14C]glutamine highlighted the importance of this amino acid as an energy source. The relative enzyme activities and the amount of ammonia produced during growth indicated that glutamine is oxidized preferentially via the transamination pathway. The overall rate of glutamine utilization from the growth medium was similar to the rate of [14C]glutamine uptake which suggests that transport may regulate glutamine metabolism.

Animals↗