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PubMedDate not supplied

Glutamine as an immunoenhancing nutrient.

New strategies for immunonutritional support include administration of special nutrients such as glutamine. Glutamine is important in several key metabolic processes of immune cells and enterocytes. Exogenous glutamine augments the functions of lymphocytes and macrophages. Neutrophils also reportedly utilize glutamine at a significant rate. Our recent studies demonstrated that glutamine enhances neutrophil function. This article focuses on the effects of glutamine on neutrophil function in surgical stress. Enteral glutamine administration enhanced peritoneal and hepatic bacterial clearance in our rat peritonitis model. Furthermore, IV glutamine supplementation improved the outcome of animals with severe surgical stress. Our in vitro study revealed that supplemental glutamine augmented the bacterial killing function of neutrophils from postoperative patients. Glutamine increased phagocytosis of the neutrophils. In addition, glutamine dose-dependently increased production of reactive oxygen intermediates (ROI) by neutrophils. Thus, our studies suggest that glutamine supplementation may improve bactericidal function of neutrophils by increasing both phagocytosis and ROI production. In conclusion, glutamine plays an important role in neutrophil function. Glutamine may be useful for the prevention, and treatment, of severe infection in critical illness and trauma.

Animals↗
PubMed2002

Glutamine supplementation and deprivation: effect on artificially reared rat small intestinal morphology.

The mechanisms of how glutamine benefits critically ill patients have not been established. The purpose of this study was to determine the effects of dietary and endogenously produced glutamine on small intestinal morphology using light and transmission electron microscopy in artificially reared rat pups. It was hypothesized that deprivation of dietary glutamine leads to intestinal disease that is exacerbated by inhibition of glutamine synthetase by methionine sulfoximine (MS). Rat pups were placed into five different test groups: The first was a reference group that was reared by their mother. The other four groups were reared artificially and received a 10% Travasol amino acid solution at 5 g/kg per day, which does not contain glutamine, added to a mixture containing carbohydrates, lipids, and vitamins. This dose was chosen because it represents an approximation of the amount of glutamine these rats would be receiving in a normal rat diet (approximately 40 g/kg per day total protein, 10 to 15% of which is glutamine + glutamate). The glutamine was manipulated by adding glutamine (Q) or MS or both. The four groups were as follows: MS-Q-, MS-Q+, MS+Q-, and MS+Q+. Light microscopy revealed the greatest blunting of villus height in the ileum of rats from the MS+Q- group when compared with the MS-Q+ group (123 +/- 48.9 micro m versus 207 +/- 36 microm, p < 0.05). The other two groups exhibited intermediate villus heights, but all were shorter than the villi from the mother-reared animals. The number of villi per unit length of bowel was also lowest in the animals that were treated with MS and not provided with dietary glutamine. Transmission electron microscopy demonstrated breakdown of the epithelial junctions in the glutamine-deprived and glutamine synthetase-inhibited intestines. Glutamine-deprived animals also displayed sloughing of microvilli, decreased actin cores, and degeneration of the terminal web. In summary, these studies support the hypothesis that glutamine is involved with maintenance of intestinal epithelial integrity.

Amino Acids↗
PubMed2026

A novel glutamine metabolism-based classification system for characterizing the heterogeneity of hepatocellular carcinoma.

BACKGROUND: Glutamine dependence is a hallmark of tumor cell metabolism, and further molecular classification based on glutamine metabolism in patients with hepatocellular carcinoma (HCC) may provide clinical value. This study thus comprehensively examined the patterns of HCC-specific alterations in glutamine metabolism. METHODS: Consensus clustering analysis was conducted on samples from The Cancer Genome Atlas-Liver Hepatocellular Carcinoma (TCGA-LIHC) dataset based on glutamine metabolism-related genes, which was validated in the GSE76427, the Liver Cancer-France (LICA-FR) cohort, and the Liver Cancer-Japan (LIRI-JP) cohort from the ICGC. Somatic mutation features were evaluated with the Maftools package in R. The activity of oncogenic pathways was estimated via gene set enrichment analysis (GSEA) or single-sample GSEA (ssGSEA). The tumor microenvironment was analyzed using both the CIBERSORT algorithm (for immune cell infiltration estimation) and the ESTIMATE algorithm (for stromal and immune score calculation). Drug sensitivity and immune checkpoint blockade (ICB) response were also analyzed, for which a classifier was built via least absolute shrinkage and selection operator (LASSO). Immunohistochemistry (IHC) was performed to validate the protein expression levels of key differentially expressed genes (DEGs). Intracellular glutamine content under different glutamine concentrations was measured. The viability of HCC cell lines under varying glutamine concentrations was assessed via Cell Counting Kit-8 (CCK-8) assays. Cell migration and invasion were evaluated through Transwell assays, and protein expression was analyzed via Western blotting. RESULTS: HCC samples were classified into two glutamine metabolism-based clusters, with cluster 1 having a more advanced stage of disease and shorter survival than cluster 2. A higher frequency of genetic mutations and stronger activation of oncogenic pathways was found in cluster 1. There were substantial differences in immune cell infiltration and stromal scores between clusters 1 and 2. Cluster 1 exhibited significantly higher infiltration of immunosuppressive cells and lower stromal scores compared to cluster 2. Cluster 1 had a stronger response to ICB due as indicated by a higher tumor mutation burden (TMB) and T cell-inflamed gene expression profile score, immune checkpoints, and Tumor Immune Dysfunction and Exclusion (TIDE)-predicted data. Moreover, the LASSO classifier accurately differentiated the two clusters. The DEGs between the two clusters were validated in clinical samples. IHC confirmed the differential expression of glutamine metabolism-related genes in HCC samples. CCK-8 assays showed no significant effect of glutamine concentration on cell proliferation. However, Transwell assays revealed that glutamine deprivation (0.2 mM) reduced migration and invasion, while high-glutamine conditions (10 mM) promoted them. Western blotting showed increased expression of metabolism-related proteins under high-glutamine conditions and reduced expression under deprivation. CONCLUSIONS: Altogether, these findings indicate the involvement of glutamine metabolism in HCC and may help inform patient stratification and the formulation of precision therapeutics for this population.

Hepatocellular carcinoma (HCC)↗
PubMed1998

Glutamine, exercise and immune function. Links and possible mechanisms.

Glutamine is the most abundant free amino acid in human muscle and plasma and is utilised at high rates by rapidly dividing cells, including leucocytes, to provide energy and optimal conditions for nucleotide biosynthesis. As such, it is considered to be essential for proper immune function. During various catabolic states including surgical trauma, infection, starvation and prolonged exercise, glutamine homeostasis is placed under stress. Falls in the plasma glutamine level (normal range 500 to 750 mumol/L after an overnight fast) have been reported following endurance events and prolonged exercise. These levels remain unchanged or temporarily elevated after short term, high intensity exercise. Plasma glutamine has also been reported to fall in patients with untreated diabetes mellitus, in diet-induced metabolic acidosis and in the recovery period following high intensity intermittent exercise. Common factors among all these stress states are rises in the plasma concentrations of cortisol and glucagon and an increased tissue requirement for glutamine for gluconeogenesis. It is suggested that increased gluconeogenesis and associated increases in hepatic, gut and renal glutamine uptake account for the depletion of plasma glutamine in catabolic stress states, including prolonged exercise. The short term effects of exercise on the plasma glutamine level may be cumulative, since heavy training has been shown to result in low plasma glutamine levels (< 500 mumol/L) requiring long periods of recovery. Furthermore, athletes experiencing discomfort from the overtraining syndrome exhibit lower resting levels of plasma glutamine than active healthy controls. Therefore, physical activity directly affects the availability of glutamine to the leucocytes and thus may influence immune function. The utility of plasma glutamine level as a marker of overtraining has recently been highlighted, but a consensus has not yet been reached concerning the best method of determining the level. Since injury, infection, nutritional status and acute exercise can all influence plasma glutamine level, these factors must be controlled and/or taken into consideration if plasma glutamine is to prove a useful marker of impending overtraining.

Animals↗
PubMed1980

Dibutyryl cyclic AMP decreases glutamine synthetase in cultured 3T3-L1 adipocytes.

Glutamine synthetase specific activity increases greater than 100-fold during the insulin-mediated differentiation of confluent 3T3-L1 cells into adipocytes. Incubation of the adipocytes for 22 h with 0.5 mM dibutyryl cyclic AMP plus 0.5 mM theophylline, 0.2 mM 8-bromo-cyclic AMP, 10 micro M epinephrine, or 1 microgram of alpha 1-24 adrenocorticotropic hormone/ml decreased glutamine synthetase by greater than 60%. During the same incubation period, there was no effect of these compounds on protein or on the specific activities of glucose-6-P dehydrogenase or hexokinase. In the presence of 0.5 mM theophylline, the dibutyryl cyclic AMP-mediated decrease in glutamine synthetase activity was half-maximal at 50 micro M dibutyryl cyclic AMP. Furthermore, between 10 micro M and 5 mM dibutyryl cyclic AMP, the dibutyryl cyclic AMP-mediated decrease in glutamine synthetase was similar in the absence or presence of 1 microgram of insulin/ml. Immunotitration of glutamine synthetase activity from 3T3 adipocytes indicates that the dibutyryl cyclic AMP-mediated decrease in the activity is due to a decrease in the cellular content of glutamine synthetase molecules. We studied the effects of dibutyryl cyclic AMP on the synthesis and degradation of glutamine synthetase. Synthesis rate was estimated from the incorporation of L-[35S]methionine into glutamine synthetase during a 60-min incubation period. Degradation rate was estimated from the first order disappearance of radioactivity from glutamine synthetase in 3T3 adipocytes previously incubated with L-[35S]methionine. Glutamine synthetase was isolated by immunoprecipitation followed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Incubation of 3T3 adipocytes with dibutyrl cyclic AMP resulted in a rapid decline in the apparent synthesis rate of glutamine synthetase. In addition, dibutyryl cyclic AMP treatment increased the initial rate of glutamine synthetase degradation. The half-life of glutamine synthetase was 24.5 h in control cultures and 16 h in dibutyryl cyclic AMP-treated cultures. In contrast, dibutyryl cyclic AMP had little effect on the synthesis or degradation of soluble protein. Our data indicate that the dibutyryl cyclic AMP-mediated decrease in 3T3 adipocyte glutamine synthetase activity results from a decrease in the synthesis rate and an increase in the initial degradation rate of the enzyme.

Adipose Tissue↗
PubMed1997

Alterations in oxidative metabolism and glutamine transport support glucose production in the tumor-influenced hepatocyte.

Glutamine is the primary substrate whose hepatic transport is upregulated in the tumor-bearing host; however, the subsequent metabolism of transported glutamine is currently unknown. The purpose of this study was to determine if glutamine is an important oxidative fuel source for hepatocytes in cancer. Specifically we compare rates of glutamine transport and oxidation in hepatocytes from control and tumor-bearing animals. We also compare rates of glucose oxidation and rates of glucose production from glutamine in control hepatocytes versus those from tumor-bearing animals. Hepatocytes from rats bearing the MCA fibrosarcoma were isolated when tumors comprised 5 and 15% of total body weight and compared to sham-implanted and pair-fed control animals. [3H]GLN transport, GLN and glucose oxidation to CO2, and glucose production from glutamine were assayed. Tumor burden of 5% stimulated a 2.52-fold increase in hepatocyte glutamine transport and a 2-fold increase when tumor burden reached 15%. Rates of oxidation of glutamine were suppressed by 1.5-fold when tumors comprised 5% of body weight compared to sham animals and were equivalent to sham animals when tumors comprised 15% of body weight. Significant alterations in glucose oxidation were observed when tumors were both small and large-glucose oxidation was suppressed by 3.6- and 3.7-fold when tumors comprised 5 and 15% of body weight respectively compared to sham-implanted rats. Incubation of hepatocytes from tumor-bearing animals with glutamine as a gluconeogenic substrate induced a 1.84-fold increase in glucose production compared to sham hepatocytes. In conclusion, (i) despite a doubling of GLN transport by the tumor-influenced hepatocyte, GLN oxidation by hepatocytes was not increased. (ii) Glucose oxidation by hepatocytes from tumor-bearing animals was decreased compared to sham hepatocytes and, simultaneously, glucose production by tumor-influenced hepatocytes from glutamine was increased. The augmentation of hepatic glutamine transport and decreased glutamine oxidation seen in tumor-influenced hepatocytes appear to support hepatocyte gluconeogenesis from glutamine.

Animals↗
PubMed1999

Glutamine and the immune system.

Glutamine is utilised at a high rate by cells of the immune system in culture and is required to support optimal lymphocyte proliferation and production of cytokines by lymphocytes and macrophages. Macrophage-mediated phagocytosis is influenced by glutamine availability. Hydrolysable glutamine dipeptides can substitute for glutamine to support in vitro lymphocyte and macrophage functions. In man plasma and skeletal muscle glutamine levels are lowered by sepsis, injury, burns, surgery and endurance exercise and in the overtrained athlete. The lowered plasma glutamine concentrations are most likely the result of demand for glutamine (by the liver, kidney, gut and immune system) exceeding the supply (from the diet and from muscle). It has been suggested that the lowered plasma glutamine concentration contributes, at least in part, to the immunosuppression which accompanies such situations. Animal studies have shown that inclusion of glutamine in the diet increases survival to a bacterial challenge. Glutamine or its precursors has been provided, usually by the parenteral route, to patients following surgery, radiation treatment or bone marrow transplantation or suffering from injury. In most cases the intention was not to stimulate the immune system but rather to maintain nitrogen balance, muscle mass and/or gut integrity. Nevertheless, the maintenance of plasma glutamine concentrations in such a group of patients very much at risk of immunosuppression has the added benefit of maintaining immune function. Indeed, the provision of glutamine to patients following bone marrow transplantation resulted in a lower level of infection and a shorter stay in hospital than for patients receiving glutamine-free parenteral nutrition.

Animals↗
PubMed1984

Glutamine promotes colony formation in bone marrow and HL-60 cells; accelerates myeloid differentiation in induced HL-60 cells.

Several studies indicate that glutamine is a critical requirement for growth of cultured cells. The present studies describe the effect of deprivation of glucose or glutamine on mouse bone marrow cell or HL-60 cell colony formation in soft agar. The mouse bone marrow cells were induced to undergo granulocyte/macrophage type differentiation by colony-stimulating factor. Glutamine, but not glucose, was found to be an indispensable metabolite for the cloning of HL-60 cells or differentiated mouse bone marrow cells. In addition, the effect of glucose or glutamine on the rate of differentiation of dimethylsulfoxide (DMSO)-induced HL-60 cells in liquid culture was studied. Glutamine was found to be superior to glucose in its ability to support the proliferation and myeloid differentiation of HL-60 cells. When an optimal concentration of DMSO was used, the rate of differentiation of induced HL-60 cells was found to be a function of the concentration of glutamine. In addition to these studies glutamine utilization and product formation was studied in induced and uninduced HL-60 cells after 60 min incubation with 1 mM initial glutamine concentration. The fractional distribution of the glutamine carbon into its metabolic products remained unchanged in induced versus uninduced HL-60 cells. However, the rate of utilization of glutamine and product formation by terminally differentiated HL-60 cells was less than the rate of utilization of glutamine by undifferentiated HL-60 cells. The data do not explain the role of glutamine in the complex process of differentiation but establish the critical requirements for glutamine, but not glucose, in myelopoiesis.

Animals↗
PubMed2005

Glutamine regulates amino acid transport and glutathione levels in a human neuroblastoma cell line.

Both amino acid transport and glutathione play a key role in regulating cancer cell growth. Glutamine can serve as an important ATP source for cancer cells, and it can supply glutamate, a precursor for the synthesis of glutathione, by the hydrolysis of glutamine. We examined the effects of glutamine concentrations [2 mM (control), 400 microM, 200 microM, and 0 microM] on cell growth, amino acid transport, and glutathione levels in a human neuroblastoma cell line, SK-N-SH, by using cell culture technique. Cell growth rates were dependent on glutamine concentrations in culture media. Glutamate transport significantly increased in glutamine-deprived groups, and this increase was remarkable in lower glutamine groups (200 microM and 0 microM glutamine). Glutamine deprivation resulted in a significant decrease in glutathione levels by 20% compared with control, but glutathione in 0 microM glutamine was maintained with the same levels found in 400 microM and 200 microM glutamine. DNA and protein synthesis correlated directly with glutamine concentrations in culture media. Our results suggest that glutamine mediates neuroblastoma cell proliferation by regulating amino acid transport and glutathione synthesis, both when sufficient nutrients are present and when key nutrients such as glutamine are in limited supply.

Amino Acids↗
PubMed2001

Glutamine distribution in patients with ulcerative colitis and in patients with familial adenomatous polyposis coli before and after restorative proctocolectomy.

BACKGROUND AND AIMS: Restorative proctocolectomy with construction of an ileoanal pouch (IPAA) is the surgical treatment of choice for patients with ulcerative colitis (UC) or familial adenomatous polyposis (FAP). This procedure imposes an essential change in function on the terminal ileal mucosa and pouch mucosa. Glutamine is one of the major nutrients for the small-bowel mucosa; it is metabolized into glutamate and subsequently alanine in the human enterocyte. In a prospective clinical trial we compared glutamine distribution in patients with UC to that in patients with FAP before and after restorative proctocolectomy. METHODS AND PATIENTS: Concentrations of glutamine, glutamate, and alanine were measured pre- and postoperatively in the terminal ileal mucosa, pouch mucosa, skeletal muscle and venous blood of patients undergoing IPAA for UC or FAP. Healthy individuals served as controls for skeletal muscle glutamine concentration. RESULTS: After IPAA the glutamine concentration in UC patients was decreased in skeletal muscle. In the mucosa glutamine remained unaltered while glutamate and alanine concentrations increased. In plasma the glutamine concentration increased, the glutamate level fell, and the alanine level increased. In FAP patients the glutamine level was unchanged in skeletal muscle after IPAA. In mucosa the glutamine level did not change, but glutamate and alanine increased. In plasma the glutamine level remained unaltered, glutamate decreased, and alanine increased. CONCLUSION: Patients with UC or FAP before surgical therapy do not suffer from glutamine depletion. IPAA resulted in changes in the distribution of glutamine and its metabolites in skeletal muscle, plasma, and ileal pouch mucosa, particularly in patients with UC. Further studies should investigate whether characteristics in the glutamine distribution have any impact for the long-term outcome after IPAA.

Adenomatous Polyposis Coli↗
PubMed1989

Glutamine transport by rat basolateral membrane vesicles.

Glutamine, a neutral amino acid, is unlike most amino acids, has two amine moieties which underlies its importance as a nitrogen transporter and a carrier of ammonia from the periphery to visceral organs. The gastrointestinal tract utilizes glutamine as a respiratory substrate. The intestinal tract receives glutamine from the luminal side and from the arterial side through the basolateral membranes of the enterocyte. This study characterizes the transport of glutamine by basolateral membrane vesicles of the rat. Basolateral membranes were prepared by a well validated technique of separation on a percoll density gradient. Membrane preparations were enriched with Na+/K+-ATPase and showed no 'overshoot' phenomena with glucose under sodium-gradient conditions. Glutamine uptake represented transport into the intravesicular space as evident by an osmolality study. Glutamine uptake was temperature sensitive and driven by an inwardly directed sodium gradient as evident by transient accumulation of glutamine above the equilibrium values. Kinetics of glutamine uptake under both sodium and potassium gradients at glutamine concentrations between 0.01 and 0.6 mM showed saturable processes with Vmax of 0.39 +/- 0.008 and 0.34 +/- 0.05 nmol/mg protein per 15 s for both sodium-dependent and sodium-independent processes, respectively. Km values were 0.2 +/- 0.01 and 0.55 +/- 0.01 mM, respectively. pH optimum for glutamine uptake was 7.5. Imposition of negative membrane potential by valinomycin and anion substitution studies enhanced the sodium-dependent uptake of glutamine suggesting an electrogenic process, whereas the sodium-independent uptake was not enhanced suggesting an electroneutral process. Other neutral amino acids inhibited the initial uptake of glutamine under both sodium-dependent and sodium-independent conditions. We conclude that glutamine uptake by basolateral membranes occurs by carrier-mediated sodium-dependent and sodium-independent processes. Both processes exhibit saturation kinetics and are inhibited by neutral amino acids. The sodium-dependent pathway is electrogenic whereas the sodium-independent pathway is electroneutral.

Animals↗
PubMed1984

Metabolism of the alpha-amino nitrogen of glutamine in rat lens.

Rat lenses were cultured 4-24 h at 37 degrees C in balance salt medium containing 5 mM [15N]-(amino)-glutamine or 5 mM [15N]-glutamate. Free amino acids were extracted with 6% trichloroacetic acid containing alpha-aminoisobutyrate as an internal standard, and trifluoroacetyl-n-butyl (TAB) derivatives were prepared. Amino acids were quantified by gas chromatography, and 15N enrichment in amino groups of several lenticular free amino acids was determined by mass spectrometry. Culture of lenses with [15N]-(amino)-glutamine resulted in more rapid [15N]-labeling of the lenticular glutamate-glutamine pool than with [15N]-glutamate. The [15N]-(amino)-glutamine entered the lenses, and within 4 hr the lenticular glutamine-glutamate pool contained 70% amino-[15N] and had more than doubled in concentration. In contrast, [15N]-glutamate entered the lenses more slowly and lenticular glutamate-glutamine reached 30% 15N in 4 hr and 60% in 24 hr, with little change in concentration. The more rapid entry of [15N]-(amino)-glutamine resulted in more labeling of other amino acids than with [15N]-glutamate. For example, after 8 hr of culture, the lenses in [15N]-(amino)-glutamine contained a % 15N enrichment of 31 in alanine, 8 in glycine, 44 in proline, 24 in serine, 62 in aspartate-asparagine, and 78 in glutamate-glutamine, compared to values of 15, 5, 20, 13, 38, and 37 respectively for the lenses in [15N]-glutamate. The results indicate that in rat lenses the two-step process of glutamine transport and deamidation is more rapid than direct transport of glutamate. Lenses cultured with glutamine released sufficient ammonia into the culture medium to account for most of the added glutamine amido nitrogen. The data indicate that the amido nitrogen of glutamine is not utilized by the lens, but is lost to the surrounding medium. In contrast, the alpha-amino nitrogen can serve as a source of nitrogen for many important pathways of lens amino acid metabolism.

Amino Acids↗
PubMed1990

Dietary modulation of small intestinal glutamine transport in intestinal brush border membrane vesicles of rats.

The effects of a glutamine-enriched diet on the transport of glutamine across brush border membrane vesicles (BBMV) from the rat jejunum were studied to gain further insight into the effects of diet on regulating gut glutamine utilization. Following fasting, rats were randomized to one of three nutritionally complete elemental diets supplemented with glutamine, glutamate, or glycine (control). Brush border membrane vesicles were prepared by a Mg2+ aggregation/differential centrifugation technique and uptake of radioactive [3H]glutamine by the BBMV was studied using a rapid mixing/filtration technique. BBMVs from all test diet groups were enriched in alkaline phosphatase 14-fold. [3H]Glutamine uptake courses for all groups demonstrated sodium dependency, overshoots, and similar 2-hr equilibrium values. Vesicles from animals fed the glutamine-enriched diet had a 75% increase in glutamine uptake compared to those of the control diet and a 250% increase compared to those of the glutamate-enriched diet (P less than 0.05). alpha-Methylamino isobutyric acid and glycine did not significantly inhibit total [3H]glutamine uptake, whereas asparagine and glutamine inhibited total [3H]glutamine uptake compared to the mannitol control. The brush border appears to possess the glutamine selective System N transporter, the activity of which can be stimulated by providing dietary glutamine.

Amino Acids↗
PubMed1988

Role of glucocorticoids in regulating interorgan glutamine flow during chronic metabolic acidosis.

The role of glucocorticoids in external glutamine mobilization and renal utilization was evaluated in three groups of chronically acidotic rats: sham-treated controls, adrenalectomized, and adrenalectomized supplemented with triamcinolone. Chronic acidosis was induced by administering NH4Cl in their drinking solution over a three-day period. Adrenalectomized rats were supplemented by triamcinolone at a dose of 40 micrograms/100 g/d administered by pellet implantation. Interorgan glutamine flow was evaluated in the postabsorptive state by monitoring net balances across the hindquarters, gut, liver, and kidneys. In the adrenal-intact group, acidosis increased the flow of glutamine from the hindquarters to the kidneys; splanchnic bed uptake, the major glutamine sink in nonacidosis, was eliminated by virtue of hepatic reversal from net uptake to release. Adrenalectomy, in the absence of an exogenous acid load, reversed the flow of glutamine with the kidneys releasing and the hindquarters removing glutamine. Acid loading restored hindquarter glutamine release to levels seen in the intact chronically acidotic animals; however, renal extraction is much less than that exhibited by the intact animals. As a consequence, arterial glutamine concentration rose with the overflow removed by the splanchnic bed, the major glutamine sink in adrenalectomized acidotic rats. Supplementing adrenalectomized acidotic rats with triamcinolone restored glutamine extraction to values seen in intact acidotic rats. Despite the renal extraction, the large hindquarter glutamine release led to hepatic uptake and a high rate of ureagenesis. Glucocorticoids, the release of which is enhanced in metabolic acidosis, appear essential for renal glutamine extraction while playing a lesser role in modulating hindquarter glutamine release.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1989

Metabolism of glutamine in lymphocytes.

Pathways of glutamine metabolism in resting and proliferating rat thymocytes and established human T- and B-lymphoblastoid cell lines were evaluated by in vitro incubations of freshly prepared or cultured cells for one to two hours with [U14C]glutamine. Complete recovery of glutamine carbons utilized in products allowed quantification of the pathways of glutamine metabolism under the experimental conditions. Partial oxidation of glutamine via 2-oxoglutarate in a truncated citric acid cycle to CO2 and oxaloacetate, which then was converted to aspartate, accounted for 76% and 69%, respectively, of the glutamine metabolized beyond the stage of glutamate by resting and proliferating thymocytes. Similar results were obtained with the lymphoblastoid T- and B-cell lines. Complete oxidation to CO2 in the citric acid cycle via 2-oxoglutarate dehydrogenase and isocitrate dehydrogenase accounted for only 25% and 7%, respectively. In proliferating cells a substantial amount of glutamine carbons was also recovered in pyruvate, alanine, and especially lactate. The main route of glutamine and glutamate entrance into the citric acid cycle via 2-oxoglutarate in lymphocytes appears to be transamination by aspartate aminotransferase rather than oxidative deamination by glutamate dehydrogenase. In the presence of glucose as a second substrate, glutamine utilization and aspartate formation markedly decreased, but complete oxidation of glutamine carbons to CO2 increased to 37% and 23%, respectively, in resting and proliferating cells. The dipeptide, glycyl-L-glutamine, which is more stable than free glutamine, can substitute for glutamine in thymocyte cultures at higher concentrations.

Ammonia↗
PubMed2004

Stimulation of intestinal glutamine absorption in chronic metabolic acidosis.

BACKGROUND: Amino acid glutamine plays a central role in inter-organ nitrogen transfer in acidosis, a compensatory mechanism that is essential in maintaining acidbase balance. Intestinal glutamine absorption is a key exogenous glutamine source in maintaining glutamine homeostasis. The purpose of this in vivo study was to investigate the regulation of intestinal glutamine absorption during chronic metabolic acidosis. METHODS: Metabolic acidosis in adult male Sprague-Dawley rats was induced by adding 1.5% NH4Cl to drinking water. [3H]-L-glutamine transport activity across brush border membrane vesicles and glutamine transporter ATB0 messenger RNA levels by relative reverse transcriptase-polymerase chain reaction were measured in rat jejunum. Data were analyzed by t test (P < .05). RESULTS: Acidosis occurred as early as 1 day and was partially compensated by 7 days. Glutamine transport in brush border membrane vesicles was increased after 2 days of acidosis. Chronic acidosis (7 days) resulted in an 8-fold increase of glutamine transport activity. The glutamine transport maximal capacity (Vmax) was stimulated 5-fold, while the transport affinity (Km) was not affected by acidosis. Relative reverse transcriptase-polymerase chain reaction showed a 2.5-fold increase of glutamine transporter ATB0 messenger RNA levels. CONCLUSIONS: Chronic metabolic acidosis stimulates intestinal glutamine absorption via a mechanism that involves an increase of functional membrane glutamine transporter units.

Acidosis↗
PubMed2005

Effects of glutamine on post-thaw motility of stallion spermatozoa: an approach of the mechanism of action at spermatozoa level.

The cryoprotective effect of l-glutamine and an approach of its mechanism of action, in preserving motility of stallion spermatozoa during the freezing-thawing process, were studied. In Experiment 1, thirty-six ejaculates were collected from six stallions (two good, two middle, and two of poor sperm freezability) and were diluted with 10 different freezing media derived from INRA 82 medium supplemented with 20 mM HEPES and 2% (v/v) centrifuged egg yolk (BM). After thawing, sperm motility was evaluated by a computer-assisted semen motility analyser. The effects of glutamine and glycerol at different concentrations on post-thaw sperm motility were studied. A possible interaction between medium and semen freezability was investigated. Only the 50 mM glutamine + 2.5% glycerol medium significantly improved sperm motility compared to classical freezing medium (2.5% glycerol). The presence of glutamine at 50 mM was not sufficient to offset the need to use glycerol in the freezing extender. The use of glutamine at a higher concentration >100 mM in the presence of 2.5% of glycerol was toxic. Reducing the glycerol proportion from 2.5% to 2 or 1.5% in the presence of glutamine at 50, 75, and 100 mM had no influence on post-thaw motility of semen of middle and good freezability. Moreover, the substitution of 2.5% glycerol by 50 mM glutamine in BM, did not significantly change the post-thaw motility of semen of good freezability. In Experiment 2, 3H-glutamine and 3H-glycerol were used to study the kinetics of penetration of glutamine and glycerol in sperm cells. The radioactivity of each radio-labelled semen pellet was measured at different times (0, 15, 30, 60, 90, 120 min), by using a Packard tri-carb 4530 apparatus. The percentages of incorporated radioactivity (%IRA) in semen pellets were calculated at different times. The %IRA of 3H-glycerol in semen pellets were significantly higher than the %IRA of 3H-glutamine. The %IRA of 3H-glycerol in semen pellets increased greatly from time 0 to 60 min, and then it is stabilized from 60 to 120 min. In contrast, the %IRA of 3H-glutamine in semen pellets increased slightly from 0 to 60 min, then it stabilized until 120 min. These experiments demonstrate that glutamine has a synergistic cryoprotective effect with glycerol on cryopreservation of stallion spermatozoa, and suggest that glutamine acts at the extra-cellular level, independently of glycerol.

Animals↗
PubMed1985

Functional hepatocyte heterogeneity in ammonia metabolism. The intercellular glutamine cycle.

In the rat liver acinus area synthesis and glutaminase activity are predominantly localized in the periportal area, whereas glutamine synthetase activity and the transport system for glutamate in the plasma membrane are perivenous. Detoxification of ammonium ions at low concentrations occurs exclusively by glutamine synthesis, but not by urea formation. Therefore, the two pathways of ammonia detoxification in the liver acinus represent the sequence of a low-affinity, but high-capacity system (urea synthesis) and a high-affinity system (glutamine synthesis). In agreement with this finding, obtained in experiments with the metabolically- and structurally-intact perfused rat liver, is also an almost complete inhibition of perivenous glutamine synthesis without impairment of periportal urea synthesis. This was shown after induction of a perivenous liver cell necrosis following CCl4 pretreatment with the consequence of a diminished hepatic ammonia extraction. Periportal glutaminase and perivenous glutamine synthetase are simultaneously active, resulting in an intercellular (as opposed to intracellular) glutamine cycle, being under the control of hormones, pH and portal ammonia and glutamine concentrations. The intercellular glutamine cycle provides an effective means for almost complete conversion of portal ammonium ions to urea by additional substrate supply of periportal urea synthesis, by periportal glutamine degradation and by the perivenous re-synthesis of glutamine from ammonia which escaped urea synthesis. Because urea synthesis, in contrast to glutamine synthesis, is a major pathway for the removal of bicarbonate, the switching of ammonia detoxification from urea synthesis to glutamine synthesis in acidosis or vice versa in alkalosis points to an important role of the liver in maintaining pH homeostasis. The acid-base-induced changes of the route of hepatic ammonia detoxification and therefore bicarbonate removal are performed by the regulatory properties of the enzymes of the intercellular glutamine cycle.

Acid-Base Equilibrium↗