Glucose, glutamine and ketone body utilisation by resting and concanavalin A activated rat splenic lymphocytes

Differences in uterine and serum metabolome associated with metritis in dairy cows

Objectives were to evaluate differences in the uterine and serum metabolomes associated with metritis in dairy cows. Vaginal discharge was evaluated using a Metricheck device (Simcro) at 5, 7, and 11 d in milk (DIM; herd 1) or 4, 6, 8, 10, and 12 DIM (herd 2). Cows with reddish or brownish, watery, and fetid discharge were diagnosed with metritis (n = 24). Cows with metritis were paired with herdmates without metritis (i.e., clear mucous vaginal discharge or clear lochia with ≤50% of pus) based on DIM and parity (n = 24). Day of metritis diagnosis was considered study d 0. All cows diagnosed with metritis received antimicrobial therapy. The metabolome of uterine lavage collected on d 0 and 5, and serum samples collected on d 0 were evaluated using untargeted gas chromatography time-of-flight mass spectrometry. Normalized data were subjected to multivariate canonical analysis of population using the MultBiplotR and MixOmics packages in R Studio. Univariate analyses including t-test, principal component analyses, partial least squares discriminant analyses, and pathway analyses were conducted using Metaboanalyst. The uterine metabolome differed between cows with and without metritis on d 0. Differences in the uterine metabolome associated with metritis on d 0 were related to the metabolism of butanoate, amino acids (i.e., glycine, serine, threonine, alanine, aspartate, and glutamate), glycolysis and gluconeogenesis, and the tricarboxylic acid cycle. No differences in the serum metabolome were observed between cows diagnosed with metritis and counterparts without metritis on d 0. Similarly, no differences in uterine metabolome were observed between cows with metritis and counterparts not diagnosed with metritis on d 5. These results indicate that the establishment of metritis in dairy cows is associated with local disturbances in amino acid, lipid, and carbohydrate metabolism in the uterus. The lack of differences in the uterine metabolome on d 5 indicates that processes implicated with the disease are reestablished by d 5 after diagnosis and treatment.

The role of the electron transport chain in immunity

The electron transport chain (ETC) couples oxidative phosphorylation (OXPHOS) with ATP synthase to drive the generation of ATP. In immune cells, research surrounding the ETC has drifted away from bioenergetics since the discovery of cytochrome c (Cyt c) release as a signal for programmed cell death. Complex I has been shown to generate reactive oxygen species (ROS), with key roles identified in inflammatory macrophages and T helper 17 cells (T_H 17) cells. Complex II is the site of reverse electron transport (RET) in inflammatory macrophages and is also responsible for regulating fumarate levels linking to epigenetic changes. Complex III also produces ROS which activate hypoxia-inducible factor 1-alpha (HIF-1α) and can participate in regulatory T cell (T_reg ) function. Complex IV is required for T cell activation and differentiation and the proper development of T_reg subsets. Complex V is required for T_H 17 differentiation and can be expressed on the surface of tumor cells where it is recognized by anti-tumor T and NK cells. In this review, we summarize these findings and speculate on the therapeutic potential of targeting the ETC as an anti-inflammatory strategy.

Adaptation to a ketogenic diet modulates adaptive and mucosal immune markers in trained male endurance athletes

This study examined the effect of short-term adaptation to a ketogenic diet (KD) on resting and post-exercise immune markers. Using a randomized, repeated-measures, crossover design, eight trained, male, endurance athletes ingested a 31-day low carbohydrate (CHO), KD (energy intake: 4% CHO; 78% fat) or their habitual diet (HD) (energy intake: 43% CHO; 38% fat). On days 0 and 31, participants ran to exhaustion at 70% VO_2max . A high-CHO (2 g·kg^-1 ) meal was ingested prior to the pre-HD, post-HD, and pre-KD trials, with CHO (~55 g·h^-1 ) ingested during exercise, whereas a low-CHO (<10 g) meal was ingested prior to the post-KD trial, with fat ingested during exercise. Blood and saliva samples were collected at pre-exercise, exhaustion, and 1 hour post-exhaustion. T-cell-related cytokine gene expression within peripheral blood mononuclear cells (PBMCs) and whole-blood inflammatory cytokine production were determined using 24-hour multi-antigen-stimulated whole-blood cultures. Multi-antigen-stimulated PBMC IFN-γ mRNA expression and the IFN-γ/IL-4 mRNA expression ratio were higher at exhaustion in the post-KD compared with pre-KD trial (P = 0.003 and P = 0.004); however, IL-4 and IL-10 mRNA expression were unaltered (P > 0.05). Multi-antigen-stimulated whole-blood IL-10 production was higher in the post-KD compared with pre-KD trial (P = 0.028), whereas IL-1β, IL-2, IL-8, and IFN-γ production was lower in the post-HD compared with pre-HD trial (P < 0.01). Salivary immunoglobulin A (SIgA) secretion rate was higher in the post-KD compared with pre-KD trial (P < 0.001). In conclusion, short-term adaptation to a KD in endurance athletes may alter the pro- and anti-inflammatory immune cell cytokine response to a multi-antigen in vitro and SIgA secretion rate.

Noninvasive rapid detection of metabolic adaptation in activated human T lymphocytes by hyperpolarized 13C magnetic resonance

The metabolic shift induced in human CD4⁺ T lymphocytes by stimulation is characterized by an upregulation of glycolysis, leading to an augmentation in lactate production. This adaptation has already been highlighted with various techniques and reported in several previous studies. We herein propose a method to rapidly and noninvasively detect the associated increase in flux from pyruvate to lactate catalyzed by lactate dehydrogenase using hyperpolarized ¹³C magnetic resonance, a technique which can be used for in vivo imaging. It was shown that the conversion of hyperpolarized ¹³C-pyruvate to ¹³C-lactate during the one-minute measurement increased by a mean factor of 3.6 in T cells stimulated for 5 days as compared to resting T cells. This method can be extended to other metabolic substrates and is therefore a powerful tool to noninvasively analyze T cell metabolism, possibly in vivo.

Acute hyperketonaemia alters T-cell-related cytokine gene expression within stimulated peripheral blood mononuclear cells following prolonged exercise

PURPOSE

We investigated the effect of the racemic β-hydroxybutyrate precursor, R,S-1,3-butanediol (BD), on T-cell-related cytokine gene expression within stimulated peripheral blood mononuclear cells (PBMC) following prolonged, strenuous exercise.

METHODS

A repeated-measures, randomised, crossover study was conducted in nine healthy, trained male cyclists (age, 26.7 ± 5.2 years; VO_2peak, 63.9 ± 2.5 mL kg^-1 min^-1). Participants ingested 0.35 g kg^-1 of BD or placebo 30 min before and 60 min during 85 min of steady-state (SS) exercise, which preceded a ~ 30 min time-trial (TT) (7 kJ kg^-1). Blood samples were collected at pre-supplement, pre-exercise, post-SS, post-TT and 1-h post-TT. Whole blood cultures were stimulated with Staphylococcal enterotoxin B (SEB) for 24 h to determine T-cell-related interleukin (IL)-4, IL-10 and interferon (IFN)-γ mRNA expression within isolated PBMCs in vitro.

RESULTS

Serum cortisol, total circulating leukocyte and lymphocyte, and T-cell subset concentrations were similar between trials during exercise and recovery (all p > 0.05). BD ingestion increased T-cell-related IFN-γ mRNA expression compared with placebo throughout exercise and recovery (p = 0.011); however, IL-4 and IL-10 mRNA expression and the IFN-γ/IL-4 mRNA expression ratio were unaltered (all p > 0.05).

CONCLUSION

Acute hyperketonaemia appears to transiently amplify the initiation of the pro-inflammatory T-cell-related IFN-γ response to an immune challenge in vitro during and following prolonged, strenuous exercise; suggesting enhanced type-1 T-cell immunity at the gene level.

Mitochondrial Dysfunction and the Aging Immune System

Mitochondria are ancient organelles that have co-evolved with their cellular hosts, developing a mutually beneficial arrangement. In addition to making energy, mitochondria are multifaceted, being involved in heat production, calcium storage, apoptosis, cell signaling, biosynthesis, and aging. Many of these mitochondrial functions decline with age, and are the basis for many diseases of aging. Despite the vast amount of research dedicated to this subject, the relationship between aging mitochondria and immune function is largely absent from the literature. In this review, three main issues facing the aging immune system are discussed: (1) inflamm-aging; (2) susceptibility to infection and (3) declining T-cell function. These issues are re-evaluated using the lens of mitochondrial dysfunction with aging. With the recent expansion of numerous profiling technologies, there has been a resurgence of interest in the role of metabolism in immunity, with mitochondria taking center stage. Building upon this recent accumulation of knowledge in immunometabolism, this review will advance the hypothesis that the decline in immunity and associated pathologies are partially related to the natural progression of mitochondrial dysfunction with aging.

Metabolism in Immune Cell Differentiation and Function

The immune system is a central determinant of organismal health. Functional immune responses require quiescent immune cells to rapidly grow, proliferate, and acquire effector functions when they sense infectious agents or other insults. Specialized metabolic programs are critical regulators of immune responses, and alterations in immune metabolism can cause immunological disorders. There has thus been growing interest in understanding how metabolic processes control immune cell functions under normal and pathophysiological conditions. In this chapter, we summarize how metabolic programs are tuned and what the physiological consequences of metabolic reprogramming are as they relate to immune cell homeostasis, differentiation, and function.

Cytochrome c Oxidase Activity Is a Metabolic Checkpoint that Regulates Cell Fate Decisions During T Cell Activation and Differentiation

T cells undergo metabolic reprogramming with major changes in cellular energy metabolism during activation. In patients with mitochondrial disease, clinical data were marked by frequent infections and immunodeficiency, prompting us to explore the consequences of oxidative phosphorylation dysfunction in T cells. Since cytochrome c oxidase (COX) is a critical regulator of OXPHOS, we created a mouse model with isolated dysfunction in T cells by targeting a gene, COX10, that produces mitochondrial disease in humans. COX dysfunction resulted in increased apoptosis following activation in vitro and immunodeficiency in vivo. Select T cell effector subsets were particularly affected; this could be traced to their bioenergetic requirements. In summary, the findings presented herein emphasize the role of COX particularly in T cells as a metabolic checkpoint for cell fate decisions following T cell activation, with heterogeneous effects in T cell subsets. In addition, our studies highlight the utility of translational models that recapitulate human mitochondrial disease for understanding immunometabolism.

Metabolic reprogramming towards aerobic glycolysis correlates with greater proliferative ability and resistance to metabolic inhibition in CD8 versus CD4 T cells

T lymphocytes (T cells) undergo metabolic reprogramming after activation to provide energy and biosynthetic materials for growth, proliferation and differentiation. Distinct T cell subsets, however, adopt metabolic programs specific to support their needs. As CD4 T cells coordinate adaptive immune responses while CD8 T cells become cytotoxic effectors, we compared activation-induced proliferation and metabolic reprogramming of these subsets. Resting CD4 and CD8 T cells were metabolically similar and used a predominantly oxidative metabolism. Following activation CD8 T cells proliferated more rapidly. Stimulation led both CD4 and CD8 T cells to sharply increase glucose metabolism and adopt aerobic glycolysis as a primary metabolic program. Activated CD4 T cells, however, remained more oxidative and had greater maximal respiratory capacity than activated CD8 T cells. CD4 T cells were also associated with greater levels of ROS and increased mitochondrial content, irrespective of the activation context. CD8 cells were better able, however, to oxidize glutamine as an alternative fuel source. The more glycolytic metabolism of activated CD8 T cells correlated with increased capacity for growth and proliferation, along with reduced sensitivity of cell growth to metabolic inhibition. These specific metabolic programs may promote greater growth and proliferation of CD8 T cells and enhance survival in diverse nutrient conditions.

Matched and mismatched metabolic fuels in lymphocyte function

Immunological function requires metabolic support to suit the needs of lymphocytes at a variety of distinct differentiation and activation states. It is now evident that the signaling pathways that drive lymphocyte survival and activity can directly control cellular metabolism. This linkage provides a mechanism by which activation and specific signaling pathways provide a supply of appropriate and required nutrients to support cell functions in a pro-active supply rather than consumption-based metabolic model. In this way, the metabolism and fuel choices of lymphocytes are guided to specifically match the anticipated needs. If the fuel choice or metabolic pathways of lymphocytes are dysregulated, however, metabolic checkpoints can become activated to disrupt immunological function. These changes are now shown in several immunological diseases and may open new opportunities to selectively enhance or suppress specific immune functions through targeting of glucose, lipid, or amino acid metabolism.

Characterization of the metabolic phenotype of rapamycin-treated CD8+ T cells with augmented ability to generate long-lasting memory cells

Background

Cellular metabolism plays a critical role in regulating T cell responses and the development of memory T cells with long-term protections. However, the metabolic phenotype of antigen-activated T cells that are responsible for the generation of long-lived memory cells has not been characterized.

Design and Methods

Using lymphocytic choriomeningitis virus (LCMV) peptide gp33-specific CD8⁺ T cells derived from T cell receptor transgenic mice, we characterized the metabolic phenotype of proliferating T cells that were activated and expanded in vitro in the presence or absence of rapamycin, and determined the capability of these rapamycin-treated T cells to generate long-lived memory cells in vivo.

Results

Antigen-activated CD8⁺ T cells treated with rapamycin gave rise to 5-fold more long-lived memory T cells in vivo than untreated control T cells. In contrast to that control T cells only increased glycolysis, rapamycin-treated T cells upregulated both glycolysis and oxidative phosphorylation (OXPHOS). These rapamycin-treated T cells had greater ability than control T cells to survive withdrawal of either glucose or growth factors. Inhibition of OXPHOS by oligomycin significantly reduced the ability of rapamycin-treated T cells to survive growth factor withdrawal. This effect of OXPHOS inhibition was accompanied with mitochondrial hyperpolarization and elevation of reactive oxygen species that are known to be toxic to cells.

Conclusions

Our findings indicate that these rapamycin-treated T cells may represent a unique cell model for identifying nutrients and signals critical to regulating metabolism in both effector and memory T cells, and for the development of new methods to improve the efficacy of adoptive T cell cancer therapy.

Characterization of the metabolic phenotype of chronically activated lymphocytes

Activated lymphocytes proliferate, secrete cytokines, and can make antibodies. Normally activated B and T cells meet the bioenergetic demand for these processes by up-regulating aerobic glycolysis. In contrast, several lines of evidence suggest that pathogenic lymphocytes in autoimmune diseases like lupus meet ATP demands through oxidative phosphorylation. Using (13)C-glucose as a stable tracer, we found that splenocytes from mice with lupus derive the same fraction of lactate from glucose as control animals, suggesting comparable levels of glycolysis and non-oxidative ATP production. However, lupus splenocytes increase glucose oxidation by 40% over healthy control animals. The ratio between pentose phosphate cycle (PPC) activity and glycolysis is the same for each group, indicating that increased glucose oxidation is due to increased activity of the TCA cycle in lupus splenocytes. Repetitive stimulation of cultured human T cells was used to model chronic lymphocyte activation, a phenotype associated with lupus. Chronically activated T cells rely primarily on oxidative metabolism for ATP synthesis suggesting that chronic antigen stimulation may be the basis for the metabolic findings observed in lupus mice. Identification of disease-related bioenergetic phenotypes should contribute to new diagnostic and therapeutic strategies for immune diseases.

Alanyl-glutamine consumption modifies the suppressive effect of L-asparaginase on lymphocyte populations in mice

Asparaginase (Elspar) is used in the treatment of acute lymphoblastic leukemia. It depletes plasma asparagine and glutamine, killing leukemic lymphoblasts but also causing immunosuppression. The objective of this work was to assess whether supplementing the diet with glutamine modifies the effect of asparaginase on normal lymphocyte populations in the spleen, thymus, and bone marrow. Mice consuming water ad libitum with or without alanyl-glutamine dipeptide (AlaGln; 0.05 mol/L) were injected once daily with 0 or 3 international units/g body weight Escherichia coli L-asparaginase for 7 d. Tissue expression of specific immune cell surface markers was analyzed by flow cytometry. Asparaginase reduced B220+ and sIgM+ cells in the bone marrow (P < 0.05) and diminished total cell numbers in thymus (-42%) and spleen (-53%) (P < 0.05). In thymus, asparaginase depleted double positive (CD4+ CD8+) and single positive (CD4+ CD8-, CD4-CD8+) thymocytes by over 40% (P < 0.05). In spleen, asparaginase reduced CD19+ B cells to 33% of controls and substantially depleted the CD4+ and CD8+ T cell populations. CD11b-expressing leukocytes were reduced by 50% (P < 0.05). Consumption of AlaGln did not lessen the effects of asparaginase in bone marrow or thymus but mitigated cellular losses in the CD4+, CD8+, and CD11b+ populations in spleen. AlaGln also blunted the increase in eukaryotic initiation factor 2 (eIF2) phosphorylation by asparaginase in spleen, whereas eIF2 phosphorylation did not change in thymus in response to asparaginase or AlaGln. In conclusion, asparaginase reduces maturing populations of normal B and T cells in thymus, bone marrow, and spleen. Oral consumption of AlaGln mitigates metabolic stress in spleen, supporting the peripheral immune system and cell-mediated immunity during asparaginase chemotherapy.

Low oxygen tension enhances the stimulation and proliferation of human T lymphocytes in the presence of IL-2

BACKGROUND

Optimization of the culture environment for the ex vivo expansion of T cells is crucial for obtaining the large doses of cells needed for cellular immunotherapy. O2 tension is a key parameter that impacts the proliferation and quality of the expanded T cells.

METHODS

Peripheral blood mononuclear cells were stimulated with either PHA or an anti-CD3 monoclonal antibody under 5% (low) or 20% (high) O2 atmospheres. After stimulation, cells were cultured in the presence of IL-2 under either low or high O2 conditions.

RESULTS

T cells stimulated and grown under 5% O2 exhibited higher proliferation rates and a mean (n = 11) of 5.8-fold greater total expansion over T cells grown under 20% O2. Stimulation under 5% O2 produced a lasting proliferative effect even after a switch to 20% O2. Examination of apoptosis by the flow cytometry-based TUNEL assay showed a mean (n = 9) of 2.9-fold greater percentage of apoptotic cells under 20% O(2). Flow-cytometric analysis of the IL-2 receptor (CD25) showed that the normal downregulation kinetics - following stimulation-induced CD25 upregulation - were slowed under 5% O(2), such that the 5% O2 cultures had a greater number of CD25+ cells, and those CD25+ cells expressed an average (n = 6) of 41% higher levels of CD25 receptor per cell. No significant O2 tension effects were observed on other surface antigens (CD3, CD28, and CD62L) examined. The key metabolic parameters, specific glucose uptake rate, q(glu), and specific lactate production rate, q(lac), were both increased by a mean (n = 5) of 47% under 5% O2.

DISCUSSION

Beyond the physiological significance, improved T-cell proliferation under 5% O2 would allow for decreased culture times in expanding T cells for cellular immunotherapies. Evidence of increased IL-2R expression and reduced apoptosis levels under 5% O2 may help explain this phenomenon.

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.

Dietary glutamine enhances murine T-lymphocyte responsiveness

To examine the effects of dietary glutamine on lymphocyte function, male mice aged 6 wk were fed for 2 wk one of three isonitrogenous, isocaloric diets, which varied in glutamine concentration. The control diet included 200 g casein/kg, providing 19.6 g glutamine/kg; the glutamine-enriched diet provided 54.8 g glutamine/kg partly at the expense of casein; and the alanine + glycine-enriched diet provided 13.3 g glutamine/kg. The plasma concentrations of a number of amino acids varied because of the diet fed. The plasma glycine concentration was greater in mice fed the alanine + glycine-enriched diet (380 +/- 22 micromol/L) than in mice fed the control (177 +/- 17 micromol/L) or the glutamine-enriched (115 +/- 18 micromol/L) diets. The plasma glutamine concentration was greater in mice fed the glutamine-enriched diet (945 +/- 117 micromol/L) than in those fed the diet enriched with alanine + glycine (561 +/- 127 micromol/L), but was not different from that in mice fed the control diet (791 +/- 35 micromol/L). There was a significant linear relationship between the amount of glutamine in the diet and plasma glutamine concentration (r = 0.655, P = 0.015). Plasma alanine concentration was unaffected by diet. The reason for the lack of effect of increasing the amount of alanine in the diet upon its concentration in the circulation may relate to its use by the liver. Thymidine incorporation (56 +/- 18 kBq/well versus <10 kBq/well), expression of the alpha-subunit of the interleukin-2 receptor (62 versus 30% receptor positive cells) and interleukin-2 production [189 +/- 28 versus 106 +/- 5 (control) or 61 +/- 13 (alanine + glycine enriched) ng/L] were greater for concanavalin A-stimulated spleen lymphocytes from mice fed the glutamine-enriched diet compared to those from mice fed the other two diets. Thus, increasing the amount of glutamine in the murine diet enhances the ability of T lymphocytes to respond to mitogenic stimulation. Taken together, these observations suggest that increasing the oral availability of glutamine could promote the T-cell driven, cell-mediated immune response.

Glutamine requirement of proliferating T lymphocytes

Glutamine is required for lymphocyte proliferation but the site of glutamine action is not yet known. In this study, the effect of glutamine on key events that occur during lymphocyte activation [interleukin-2 (IL-2) production, IL-2 use, IL-2 receptor expression, transferrin receptor expression] was investigated. Rat or mouse spleen lymphocytes were cultured in the presence of the T-cell mitogen concanavalin A (Con A) and various concentrations of glutamine. There was a trend (not significant) for the ratio of CD4+:CD8+ spleen lymphocytes to increase (from 1.9 to 2.6) as the concentration of glutamine in culture medium increased from 0 to 2 mmol/L. As the concentration of glutamine increased, there was an increase in the proportion of cells expressing the IL-2 receptor (from 30 to 45%) and the transferrin receptor (from 34% to 55%). As the concentration of glutamine increased there was a 2.7-fold increase in the concentration of IL-2 in the culture medium. The IL-2 concentration was decreased when an IL-2 receptor-blocking antibody was included in the culture medium; the IL-2 concentrations measured were taken to indicate the initial Con A-stimulated production of IL-2. In these conditions, the IL-2 concentration in the medium increased 39-fold as the glutamine concentration increased. The use of IL-2 by an IL-2-dependent cell line was dependent on the glutamine concentration in the culture medium. Thus, all four components of lymphocyte activation investigated (IL-2 production, IL-2 use, IL-2 receptor expression, transferrin receptor expression) were dependent on the concentration of glutamine present in the culture medium. Thus, glutamine might provide an early signal in the lymphocyte activation process.

Indium-111 labelled lymphocytes: isotope distribution and cell division

Since lymphocytes continue to proliferate and divide in vivo, it is important to determine the fate of a radionulide following lymphocyte labelling. Using the mixed lymphocyte reaction (MLR), we induced indium-111 labelled lymphocytes from a specific in-bred rat strain (AS) to divide and then observed the subsequent 111In distribution between cells and supernatant. L10 and L12.4 cells, which are allospecific CD4+ T lymphocytes from the AS rat, were stimulated in the MLR by antigen-presenting cells from the August rat, a different strain. We labelled L10 or L12.4 lymphocytes on day 0, the first day of the stimulation cycle, and continued to culture the lymphocytes in vitro. The proliferation of the cells was estimated according to their increase in number. The distribution of 111In between cell and supernatant fractions and between viable and dead (but intact) cells was measured in the cell suspension each day after labelling. The metabolic activity of 111In-labelled lymphocytes was compared with control cells by measuring their uptake of fluorine-18 fluorodeoxyglucose ([18F]FDG). 111In-labelled lymphocytes showed a poor proliferative response compared with control cells 24-48 h after labelling but increased in number after this time. From 24 to 72 h, about 70% of 111In was in the supernatant but only about 5%-10% was associated with intact dead cells. These dead cells tended to retain their 111In, losing less than 30% per day, suggesting that 111In in the supernatant was the result of active elimination from viable cells. Moreover, 24 h after culture, considerably more 111In was associated with viable than with dead lymphocytes, although over the next few days this distribution reversed. 111In-labelled lymphocytes took up more [18F]FDG than control cells at 24 h but not at 0 or 72-96 h; the maximum [18F]FDG uptake coincided with the greatest reduction in cell number. Furthermore, [18F]FDG uptake correlated with the initial 111In burden in lymphocytes labelled with 111In 24 h previously. The results are consistent with active elimination of 111In by 111In-labelled lymphocytes. The energy requirements for this are diverted away from cell division, thereby increasing the probability of cell death. As lymphocytes become 111In deplete, they recover their capacity to proliferate and their risk of death decreases. These findings have important implications for 111In-labelled lymphocyte scintigraphy, suggesting that cells remaining viable immediately after labelling will either subsequently die or alternatively eliminate the label.

Cell susceptibility to apoptosis by glutamine deprivation and rescue: survival and apoptotic death in cultured lymphoma-leukemia cell lines

Human leukemia/lymphoma cells maintained in culture medium without provision of fresh nutrients lose viability and die by a process resembling apoptosis within a few days. Upon incubation in an FCS-supplemented RPMI 1640 medium containing 2 mM L-glutamine CEM, Namalwa, HL-60 and U937 cells, seeded at initial densities of 0.2 to 1 x 10(6) cells/ml, ceased growing within 3-5 days and progressively entered an apoptotic pathway, as assessed by nucleosomal DNA fragmentation and morphology. Both the major energy-source nutrients in the medium, glucose and glutamine, became rapidly exhausted during the incubation. Further studies were performed using CEM cells. Incubation in glutamine-free or glucose-free medium renewed every 24 h showed that glutamine deprivation is associated with cell death by apoptosis independent of energetic failure, whereas glucose deprivation is followed by rapid loss of mitochondrial function with sharp drop of intracellular ATP and cell death by necrosis. A 12-24 h incubation in glutamine-depleted medium was required to direct the cells toward the apoptotic pathway. Growth arrest followed by apoptotic death was detected in CEM cells when medium glutamine concentration remained below 0.3-0.4 mM for at least 24 h, but a reinstatement of medium glutamine to 2 mM within this period rescued the cells from growth arrest and death.

Comparative analysis of glucose and glutamine metabolism in transformed mammalian cell lines, insect and primary liver cells

Glucose and glutamine metabolism in several cultured mammalian cell lines (BHK, CHO, and hybridoma cell lines) were investigated by correlating specific utilization and formation rates with specific maximum activities of regulatory enzymes involved in glycolysis and glutaminolysis. Results were compared with data from two insect cell lines and primary liver cells. Flux distribution was measured in a representative mammalian (BHK) and an insect (Spodoptera frugiperda) cell line using radioactive substrates. A high degree of similarity in many aspects of glucose and glutamine metabolism was observed among the cultured mammalian cell lines examined. Specific glucose utilization rates were always close to specific hexokinase activities, indicating that formation of glucose-6-phosphate from glucose (catalyzed by hexokinase) is the rate limiting step of glycolysis. No activity of the key enzymes connecting glycolysis with the tricarboxylic acid cycle, such as pyruvate dehydrogenase, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase, could be detected. Flux distribution in BHK cells showed glycolytic rates very similar to lactate formation rates. No glucose- or pyruvate-derived carbon entered the tricarboxylic acid cycle, indicating that glucose is mainly metabolized via glycolysis and lactate formation. About 8% of utilized glucose was metabolized via the pentose phosphate shunt, while 20 to 30% of utilized glucose followed pathways other than glycolysis, the tricarboxylic acid cycle, or the pentose phosphate shunt. About 18% of utilized glutamine was oxidized, consistent with the notion that glutamine is the major energy source for mammalian cell lines. Mammalian cells cultured in serum-free low-protein medium showed higher utilization rates, flux rates, and enzyme activities than the same cells cultured in serum-supplemented medium. Insect cells oxidized glucose and pyruvate in addition to glutamine. Furthermore, insect cells produced little or no lactate and were able to channel glycolytic intermediates into the tricarboxylic acid cycle. Metabolic profiles of the type presented here for a variety of cell lines may eventually enable one to interfere with the metabolic patterns of cells relevant to biotechnology, with the hope of improving growth rate and/or productivity.

Effect of HCO3- on glutamine and glucose metabolism in lymphocytes

Lymphocytes play a quantitatively important role in glutamine utilization in the body. We hypothesized that in metabolic acidosis characterized by decreased extracellular HCO3- concentration ([HCO3-]), glutamine utilization by lymphocytes may decrease to compensate partially for the increased uptake of glutamine by the kidneys for ammoniagenesis. This study was therefore designed to quantify the effect of extracellular [HCO3-] on glutamine metabolism in lymphocytes relative to glucose utilization. Mesenteric lymph node lymphocytes were incubated at 37 degrees C for 1 hour in Krebs-Henseleit buffer containing 0, 12.5, and 25 mmol/L HCO3- at a constant pH of 7.4 or 15.7 and 25 mmol/L HCO3- at a constant CO2 concentration of 1.25 mmol/L. Reducing extracellular [HCO3-] from 25 to 12.5 mmol/L at constant pH or from 25 to 15.7 mmol/L at constant CO2 concentration decreased glutamine utilization and the production of glutamate and ammonia. A reduction in [HCO3-] from 12.5 to 0 mmol/L further decreased glutamine utilization, as well as the production of all measured glutamine metabolites. Interestingly, decreasing [HCO3-] from 25 to 0 mmol/L had no significant effect on glucose metabolism, although the production of pyruvate (a minor product of glucose in lymphocytes) was decreased in the absence of medium HCO3-. The contribution of glutamine but not of glucose to lymphocyte adenosine triphosphate (ATP) production was decreased with reduced extracellular [HCO3-]. Thus, glucose was a more important fuel for lymphocytes than was glutamine at low [HCO3-].(ABSTRACT TRUNCATED AT 250 WORDS)

Luminal glutamine perfusion alters endotoxin-related changes in ileal permeability of the piglet

BACKGROUND

The objective of this study was to investigate whether luminal perfusion with glutamine or with oxygenated glutamine solutions prevents endotoxin-induced changes in mucosal permeability.

METHODS

Three 15-cm segments of distal ileum were isolated in anesthetized 21-day-old piglets (n = 4) and perfused (50 mL/h) with Ringer's lactate solution, Ringer's lactate solution with 2% glutamine (wt/vol), glutamine, or glutamine purged with oxygen at 37 degrees C for 280 minutes. Plasma-to-lumen clearances of 51Cr-EDTA and urea were measured to assess mucosal permeability. At time 0 minutes, loading and maintenance IV infusions of markers were begun. Baseline permeabilities were obtained from time 60 to 80 minutes, and IV endotoxin (50 micrograms/kg) was introduced from time 80 to 140 minutes.

RESULTS

Results are expressed as the ratio of the clearances of the two probes (CEDTA/CUREA). Permeability increased from baseline in loops perfused with Ringer's lactate solution vs loops perfused with glutamine purged with oxygen and with glutamine alone (p < .01). Saturation with oxygen was without effect inasmuch as glutamine alone negated permeability increases. Intestinal myeloperoxidase activity did not differ with perfusate (p > .05).

CONCLUSIONS

These data suggest that endotoxin-induced permeability changes can be prevented or delayed by the supply of luminal glutamine at the time of insult.

Profile of energy metabolism in a murine hybridoma: glucose and glutamine utilization

The antibody-secreting murine hybridoma, CC9C10, was grown in batch culture in a medium containing 20 mM glucose and 2 mM glutamine. After 2 days of exponential growth, the glutamine content of the medium was completely depleted, whereas the glucose content was reduced to 60% of the original concentration. The glucose and glutamine metabolism was analyzed at midexponential phase by use of radioactively labelled substrates. Glycolysis accounted for the metabolism of most of the glucose utilized (> 96%) with flux through the pentose phosphate pathway (3.6%) and the TCA cycle (0.6%) accounting for the remainder. Glutamine was partially oxidised via glutaminolysis to alanine (55%), aspartate (3%), glutamate (4%), lactate (9%), and CO2 (22%). Calculation of the theoretical ATP production from these pathways indicated that glucose could provide 59% and glutamine 41% of the energy requirement of the cells.

The effects of 3-hydroxybutyrate and glucose on human T cell responses to Candida albicans

Diabetic patients are particularly susceptible to mucocutaneous candidosis. T lymphocytes are central to the induction of antigen-specific immune responses and may be sensitive to the biochemical abnormalities associated with poorly controlled diabetes; namely, hyperglycaemia and/or ketonemia. To examine this we have studied the effect of varying concentrations of glucose and 3-hydroxybutyrate (3-HB) in cultures of human T cells stimulated with Candida albicans antigen. Proliferation of T cells from six type 1 diabetic and six non-diabetic control subjects was significantly inhibited (both P < 0.05) in glucose-free medium, and at a glucose concentration of 80 mmol l-1 as compared with cultures containing glucose at physiological concentration (5 mmol l-1). 16 and 32 mmol l-1 3-HB also inhibited T cell proliferation in the presence of 5 mmol l-1 glucose (P < 0.05). The effect of glucose and 3-HB were not additive and the inhibition was not due to cell death. 32 mmol l-1 3-HB had less effect when present solely during antigen pulsing than during subsequent lymphocyte stimulation, and was effective even when added after 72 h of a six day culture. This suggests that ketosis affects T cell proliferation more than antigen processing and presentation. We conclude that human antigen-specific T cell proliferation is inhibited in vitro only by concentrations of 3-HB encountered in moderately severe diabetic ketoacidosis, and by glucose concentrations found in severe hyperosmolar non-ketotic coma. The impairment of T cell function under such extreme conditions could be implicated in the close association of diabetic ketoacidosis with deep fungal infections, particularly invasive mucormycosis.

Glucose and glutamine metabolism of a murine B-lymphocyte hybridoma grown in batch culture

The energy metabolism of a mammalian cell line grown in vitro was analyzed by substrate consumption rates and metabolic flux measurements. The data allowed the determination of the relative importance of the pathways of glucose and glutamine metabolism to the energy requirements of the cell. Changes in the substrate concentrations during culture contributed to the changing catalytic activities of key enzymes, which were determined. 1. A murine B-lymphocyte hybridoma (PQXB1/2) was grown in batch culture to a maximum cell density of 1-2 x 10(6) cells/mL in 3-4 d. The intracellular protein content showed a maximum value during the exponential growth phase of 0.55 mg/10(6) cells. Glutamine was completely depleted, but glucose only partially depleted to 50% of its original concentration when the cells reached a stationary phase following exponential growth. 2. The specific rates of glutamine and glucose utilization varied during culture and showed maximal values at the midexponential phase of 2.4 nmol/min/10(6) cells and 4.3 nmol/min/10(6) cells, respectively. 3. A high proportion of glucose (96%) was metabolized by glycolysis, but only limited amounts by the pentose phosphate pathway (3.3%) and TCA cycle (0.21%). 4. The maximum catalytic activity of hexokinase approximates to the measured flux of glycolysis and is suggested as a rate-limiting step. In the stationary phase, the hexokinase activity reduced to 11% of its original value and may explain the reduced glucose utilization at this stage. 5. The maximal activities of two TCA cycle enzymes were well above the measured metabolic flux and are unlikely to pose regulatory barriers. However, the activity of pyruvate dehydrogenase was undetectable by spectrophotometric assay and explains the low level of flux of glycolytic metabolites into the TCA cycle. 6. A significant proportion of the glutamine (36%) utilized by the cells was completely oxidized to CO2. 7. The measured rate of glutamine transport into the cells approximated to the metabolic flux and is suggested as a rate-limiting step. 8. Glutamine metabolism is likely to occur via glutaminase and amino transaminase, which have significantly higher activities than glutamate dehydrogenase. 9. The calculated potential ATP production suggests that, overall, glutamine is the major contributor of cellular energy. However, at the midexponential phase, the energy contribution from the catabolism of the two substrates was finely balanced--glutamine (55%) and glucose (45%).

The effects of a leukaemia-controlling dose of acivicin on murine splenic lymphocytes in vitro and in vivo

The development of successful chemotherapy for cancers, including leukaemia, is based on the exploitation of significant toxic differentials of the agents, between the cancer cells and their normal counterparts. A concentration of 0.1 mumol/L of the amino acid analogue acivicin (L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid) was sufficient to inhibit [3H]-DNA synthesis in mitogen stimulated murine splenic lymphocytes and WEHI 7.1 murine leukaemic cells in vitro, at glutamine concentrations up to 0.5 mmol/L. However, at concentrations of glutamine of 1.0 mmol/L and above, more acivicin was required to inhibit WEHI 7.1 cells than to inhibit the splenic lymphocytes. At 1.0 mmol/L glutamine, 18 h of exposure to an optimal inhibitory concentration of acivicin (0.5 mumol/L) in vitro was sufficient to inhibit [3H]-DNA synthesis in the mitogen stimulated lymphocytes, whereas 24 h of exposure to an optimal inhibitory acivicin concentration of 2.0 mumol/L was required for inhibition of [3H]-DNA synthesis in the WEHI 7.1 leukaemic cells. When an acivicin inoculation regime that was sufficient to control the growth of intraperitoneally (i.p.) implanted WEHI 7.1 leukaemic cells was administered to Balb/c mice, the primary immune response was significantly inhibited to an antigen given either during or after the acivicin treatment. These results indicate that lymphocytes replicating in vivo in a specific primary immune response could be as sensitive to acivicin as leukaemic cells.

Lactate production is the major metabolic fate of glucose in splenocytes and is altered in spontaneously diabetic BB rats

Enhanced glucose metabolism is necessary to support the activation and proliferation of lymphocytes. To define further quantitatively the metabolic fates of glucose and assess glucose utilization both in normal cells and in an autoimmune disease with abnormal lymphocytes, [U-14C]glucose conversion into 14CO2 and the production of lactate and pyruvate were measured in splenocytes. Cells from non-diabetes-prone (BBn) and spontaneously diabetic (BBd) rats were studied both freshly isolated 'resting' and cultured for 96 h with and without concanavalin A (Con A) stimulation. (1) Lactate was confirmed to be the major end product in both freshly isolated (53% of utilized glucose) and unstimulated cultured (62% of utilized glucose) cells from BBn animals studied at (2-8) x 10(6) cells/ml concentration. The use of concentrations from 10 x 10(6) to 300 x 10(6) cells/ml resulted in progressively less lactate production per 10(6) splenocytes. (2) Cells from BBd animals after stimulation with Con A incorporated less [3H]thymidine and produced significantly less lactate (155 +/- 14 versus 305 +/- 24 nmol/2 h per 10(6) cells) than did BBn cells (P less than 0.05). (3) However, more lactate (101 +/- 8 versus 78 +/- 6 nmol/5 h per 10(6) cells) was produced by 'resting' cells from BBd animals compared with BBn (P less than 0.03), and this difference was sustained after 4 days in culture. (4) Significantly greater amounts of pyruvate were produced by BBd than by BBn cells, particularly when stimulated with Con A, suggesting an alteration in the availability of reducing equivalents in BBd cells. (5) These results are consistent with prior metabolic as well as immunological 'activation' of cells in vivo in the BB diabetic animals.

The effect of glutamine on murine splenic leukocyte responses to T and B cell mitogens

Murine splenic leukocytes cannot be stimulated to synthesize [3H]-DNA by various concentrations of either the T cell mitogens, Concanavalin-A (Con-A) or phytohaemagglutinin (PHA) or the B cell mitogen, lipopolysaccharide (LPS), unless glutamine is present in the culture medium. The optimum concentration of the T cell mitogens (Con-A, PHA) remained constant for all levels of glutamine while that of the B cell mitogen (LPS) increased as the concentration of glutamine in the medium increased.