Comparison between transport and degradation of leucine and glutamine by peripheral human lymphocytes exposed to concanavalin A

Productive and physiological implications of top-dress addition of branched-chain amino acids and arginine on lactating sows and offspring

BACKGROUND

Branched-chain amino acids (BCAAs), including L-leucine (L-Leu), L-isoleucine (L-Ile), L-valine (L-Val), and L-arginine (L-Arg), play a crucial role in mammary gland development, secretion of milk and regulation of the catabolic state and immune response of lactating sows. Furthermore, it has recently been suggested that free amino acids (AAs) can also act as microbial modulators. This study aimed at evaluating whether the supplementation of lactating sows with BCAAs (9, 4.5 and 9 g/d/sow of L-Val, L-Ile and L-Leu, respectively) and/or L-Arg (22.5 g/d/sow), above the estimated nutritional requirement, could influence the physiological and immunological parameters, microbial profile, colostrum and milk composition and performance of sows and their offspring.

RESULTS

At d 41, piglets born from the sows supplemented with the AAs were heavier (P = 0.03). The BCAAs increased glucose and prolactin (P < 0.05) in the sows' serum at d 27, tended to increase immunoglobulin A (IgA) and IgM in the colostrum (P = 0.06), increased the IgA (P = 0.004) in the milk at d 20 and tended to increase lymphocyte% in the sows' blood at d 27 (P = 0.07). Furthermore, the BCAAs tended to reduce the Chao1 and Shannon microbial indices (P < 0.10) in the sows' faeces. The BCAA group was discriminated by Prevotellaceae_UCG-004, Erysipelatoclostridiaceae UCG-004, the Rikenellaceae_RC9_gut_group and Treponema berlinense. Arginine reduced piglet mortality pre- (d 7, d 14) and post-weaning (d 41) (P < 0.05). Furthermore, Arg increased the IgM in the sow serum at d 10 (P = 0.05), glucose and prolactin (P < 0.05) in the sow serum at d 27 and the monocyte percentage in the piglet blood at d 27 (P = 0.025) and their jejunal expression of NFKB2 (P = 0.035) while it reduced the expression of GPX-2 (P = 0.024). The faecal microbiota of the sows in Arg group was discriminated by Bacteroidales. The combination of BCAAs and Arg tended to increase spermine at d 27 (P = 0.099), tended to increase the Igs (IgA and IgG, P < 0.10) at d 20 in the milk, favoured the faecal colonisation of Oscillospiraceae UCG-005 and improved piglet growth.

CONCLUSION

Feeding Arg and BCAAs above the estimated requirements for milk production may be a strategy to improve sow productive performance in terms of piglet average daily gain (ADG), immune competence and survivability via modulation of the metabolism, colostrum and milk compositions and intestinal microbiota of the sows. The synergistic effect between these AAs, noticeable by the increase of Igs and spermine in the milk and in the improvement of the performance of the piglets, deserves additional investigation.

Clinical Metabolomics Identifies Blood Serum Branched Chain Amino Acids as Potential Predictive Biomarkers for Chronic Graft vs. Host Disease

The allogeneic hematopoietic stem cell transplantation procedure—the only curative therapy for many types of hematological cancers—is increasing, and graft vs. host disease (GVHD) is the main cause of morbidity and mortality after transplantation. Currently, GVHD diagnosis is clinically performed. Whereas, biomarker panels have been developed for acute GVHD (aGVHD), there is a lack of information about the chronic form (cGVHD). Using nuclear magnetic resonance (NMR) and gas chromatography coupled to time-of-flight (GC-TOF) mass spectrometry, this study prospectively evaluated the serum metabolome of 18 Brazilian patients who had undergone allogeneic hematopoietic stem cell transplantation (HSCT). We identified and quantified 63 metabolites and performed the metabolomic profile on day −10, day 0, day +10 and day +100, in reference to day of transplantation. Patients did not present aGVHD or cGVHD clinical symptoms at sampling times. From 18 patients analyzed, 6 developed cGVHD. The branched-chain amino acids (BCAAs) leucine and isoleucine were reduced and the sulfur-containing metabolite (cystine) was increased at day +10 and day +100. The area under receiver operating characteristics (ROC) curves was higher than 0.79. BCAA findings were validated by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) in 49 North American patients at day +100; however, cystine findings were not statistically significant in this patient set. Our results highlight the importance of multi-temporal and multivariate biomarker panels for predicting and understanding cGVHD.

Post-ruminal branched-chain amino acid supplementation and intravenous lipopolysaccharide infusion alter blood metabolites, rumen fermentation, and nitrogen balance of beef steers

Steers exposed to an endotoxin may require additional branched-chain AA (BCAA) to support an increase in synthesis of immune proteins. This study evaluated effects of bacterial lipopolysaccharide (LPS) and BCAA supplementation on blood metabolites and N balance of 20 ruminally-cannulated steers (177 ± 4.2 kg BW). The experiment was a randomized block design, with 14-d adaptation to metabolism stalls and diet (DM fed = 1.5% BW) and 6-d collection. Treatments were a 2 × 2 factorial of LPS (0 vs. 1.0 to 1.5 μg/kg BW; -LPS vs. +LPS) and BCAA (0 vs. 35 g/d; -BCAA vs. +BCAA). The LPS in 100 mL sterile saline was infused (1 mL/min via i.v. catheter) on day 15. The BCAA in an essential AA solution were abomasally infused (900 mL/d) three times daily in equal portions beginning on day 7. Blood, rumen fluid, and rectal temperature were collected on day 15 at h 0, 2, 4, 8, 12, and 24 after LPS infusion. Feces and urine were collected from day 16 to 20. Rectal temperatures were greater for +LPS vs. -LPS steers at 4 h and lower at 8 h after LPS infusion (LPS × h, P < 0.01). Serum cortisol and plasma urea N were greater for +LPS than -LPS steers at 2 (cortisol only), 4, 8, 12, and 24 h after LPS infusion (LPS × h, P < 0.01). Serum cortisol was greater for +BCAA than -BCAA steers at 12 h after LPS infusion (BCAA × h, P < 0.05). Serum glucose was greater for +LPS than -LPS steers at 2 h after LPS infusion (LPS × h, P < 0.01). Plasma Ile, Leu, and Val were lower, and plasma His was greater in +LPS than -LPS steers (LPS, P < 0.05). Plasma Lys, Met, Thr, and Trp of +LPS steers were lower than -LPS steers at 4 (Thr only), 8 (Lys and Trp only), 12, and 24 h after infusion (LPS × h, P < 0.05). Plasma Ile, Leu, and Val were greater (BCAA, P < 0.01), and Met, His, Phe, Thr, and Trp were lower for +BCAA than -BCAA steers at 0 and 24 h after LPS infusion (BCAA × h, P ≤ 0.05). Steers receiving +LPS had lower rumen pH at 8 h, greater total VFA at 8 h, and lower rumen NH3 at 24 h after LPS infusion compared with -LPS steers (LPS × h, P ≤ 0.04). Total tract passage rates, DM, OM, NDF, ADF, and N intake, fecal N, digested N, and retained N were lower (P < 0.05) for +LPS than -LPS steers. Total N supply (dietary plus infused) and fecal N were greater (P < 0.05) for +BCAA vs. -BCAA steers. The absence of LPS × BCAA interactions (P ≥ 0.20) for N balance indicated that post-ruminal supplementation of BCAA did not alleviate the negative effects of endotoxin on N utilization by growing steers.

Identification of serum metabolites associated with the risk of metritis in transition dairy cows

In this study, we aimed to identify metabolite signatures that characterize metritis prior to, during, and after the disease incidence. Blood samples were collected from 100 Holstein cows at five time points before and after parturition. Six cows that developed metritis and 20 controls were selected for metabolomics analysis in a nested case-control study. Twenty nine serum metabolites were quantified using gas chromatography–mass spectroscopy. Results showed that similar panels of metabolites differentiated pre-metritic and control cows at 8 and 4 wk prepartum. The top most important metabolites that differentiated the two groups of cows at 8 wk prepartum were oxalate, ornithine, pyroglutamic acid, d-mannose, and glutamic acid, and at 4 wk prepartum were ornithine, pyroglutamic acid, d-mannose, glutamic acid, and phosphoric acid, suggesting their potential use as risk biomarkers for metritis. Area under the curve with values of 1.0 and 0.969 at 8 and 4 wk, respectively, indicated that those panels of metabolites have a very high sensitivity and specificity to be used as risk biomarkers for metritis. Overall, results showed that specific serum metabolite signatures can be used to screen cows for susceptibility to metritis during the dry off period, and to better understand the etiopathobiology of the disease.

The metabolomics of psoriatic disease

Metabolomics is an emerging new "omics" field involving the systematic analysis of the metabolites in a biologic system. These metabolites provide a molecular snapshot of cellular activity and are thus important for understanding the functional changes in metabolic pathways that drive disease. Recently, metabolomics has been used to study the local and systemic metabolic changes in psoriasis and its cardiometabolic comorbidities. Such studies have revealed novel insights into disease pathogenesis and suggest new biochemical signatures that may be used as a marker of psoriatic disease. This review will discuss common strategies in metabolomics analysis, current findings in the metabolomics of psoriasis, and emerging trends in psoriatic metabolomics.

PD-1 alters T-cell metabolic reprogramming by inhibiting glycolysis and promoting lipolysis and fatty acid oxidation

During activation, T cells undergo metabolic reprogramming, which imprints distinct functional fates. We determined that on PD-1 ligation, activated T cells are unable to engage in glycolysis or amino acid metabolism but have an increased rate of fatty acid β-oxidation (FAO). PD-1 promotes FAO of endogenous lipids by increasing expression of CPT1A, and inducing lipolysis as indicated by elevation of the lipase ATGL, the lipolysis marker glycerol and release of fatty acids. Conversely, CTLA-4 inhibits glycolysis without augmenting FAO, suggesting that CTLA-4 sustains the metabolic profile of non-activated cells. Because T cells utilize glycolysis during differentiation to effectors, our findings reveal a metabolic mechanism responsible for PD-1-mediated blockade of T-effector cell differentiation. The enhancement of FAO provides a mechanistic explanation for the longevity of T cells receiving PD-1 signals in patients with chronic infections and cancer, and for their capacity to be reinvigorated by PD-1 blockade.

Activation of T cells results in metabolic reprogramming to favour glycolysis. Here, Patsoukis et al. show that the surface receptor PD-1 inhibits glycolysis and increases the metabolism of lipids, providing a potential mechanism for the blockade of T effector functions but also for the longevity accompanying T cell exhaustion.

Metabolomics in psoriatic disease: pilot study reveals metabolite differences in psoriasis and psoriatic arthritis

Importance: While “omics” studies have advanced our understanding of inflammatory skin diseases, metabolomics is mostly an unexplored field in dermatology.

Objective: We sought to elucidate the pathogenesis of psoriatic diseases by determining the differences in metabolomic profiles among psoriasis patients with or without psoriatic arthritis and healthy controls.

Design: We employed a global metabolomics approach to compare circulating metabolites from patients with psoriasis, psoriasis and psoriatic arthritis, and healthy controls.

Setting: Study participants were recruited from the general community and from the Psoriasis Clinic at the University of California Davis in United States.

Participants: We examined metabolomic profiles using blood serum samples from 30 patients age and gender matched into three groups: 10 patients with psoriasis, 10 patients with psoriasis and psoriatic arthritis and 10 control participants.

Main outcome(s) and measures(s): Metabolite levels were measured calculating the mean peak intensities from gas chromatography time-of-flight mass spectrometry.

Results: Multivariate analyses of metabolomics profiles revealed altered serum metabolites among the study population. Compared to control patients, psoriasis patients had a higher level of alpha ketoglutaric acid (Pso: 288 ± 88; Control: 209 ± 69; p=0.03), a lower level of asparagine (Pso: 5460 ± 980; Control: 7260 ± 2100; p=0.02), and a lower level of glutamine (Pso: 86000 ± 20000; Control: 111000 ± 27000; p=0.02). Compared to control patients, patients with psoriasis and psoriatic arthritis had increased levels of glucuronic acid (Pso + PsA: 638 ± 250; Control: 347 ± 61; p=0.001). Compared to patients with psoriasis alone, patients with both psoriasis and psoriatic arthritis had a decreased level of alpha ketoglutaric acid (Pso + PsA: 186 ± 80; Pso: 288 ± 88; p=0.02) and an increased level of lignoceric acid (Pso + PsA: 442 ± 280; Pso: 214 ± 64; p=0.02).

Conclusions and relevance: The metabolite differences help elucidate the pathogenesis of psoriasis and psoriatic arthritis and they may provide insights for therapeutic development.

Induction of glucose metabolism in stimulated T lymphocytes is regulated by mitogen-activated protein kinase signaling

T lymphocytes play a critical role in cell-mediated immune responses. During activation, extracellular and intracellular signals alter T cell metabolism in order to meet the energetic and biosynthetic needs of a proliferating, active cell, but control of these phenomena is not well defined. Previous studies have demonstrated that signaling from the costimulatory receptor CD28 enhances glucose utilization via the phosphatidylinositol-3-kinase (PI3K) pathway. However, since CD28 ligation alone does not induce glucose metabolism in resting T cells, contributions from T cell receptor-initiated signaling pathways must also be important. We therefore investigated the role of mitogen-activated protein kinase (MAPK) signaling in the regulation of mouse T cell glucose metabolism. T cell stimulation strongly induces glucose uptake and glycolysis, both of which are severely impaired by inhibition of extracellular signal-regulated kinase (ERK), whereas p38 inhibition had a much smaller effect. Activation also induced hexokinase activity and expression in T cells, and both were similarly dependent on ERK signaling. Thus, the ERK signaling pathway cooperates with PI3K to induce glucose utilization in activated T cells, with hexokinase serving as a potential point for coordinated regulation.

Glutamine uptake and metabolism are coordinately regulated by ERK/MAPK during T lymphocyte activation

Activation of a naive T cell is a highly energetic event, which requires a substantial increase in nutrient metabolism. Upon stimulation, T cells increase in size, rapidly proliferate, and differentiate, all of which lead to a high demand for energetic and biosynthetic precursors. Although amino acids are the basic building blocks of protein biosynthesis and contribute to many other metabolic processes, the role of amino acid metabolism in T cell activation has not been well characterized. We have found that glutamine in particular is required for T cell function. Depletion of glutamine blocks proliferation and cytokine production, and this cannot be rescued by supplying biosynthetic precursors of glutamine. Correlating with the absolute requirement for glutamine, T cell activation induces a large increase in glutamine import, but not glutamate import, and this increase is CD28-dependent. Activation coordinately enhances expression of glutamine transporters and activities of enzymes required to allow the use of glutamine as a Krebs cycle substrate in T cells. The induction of glutamine uptake and metabolism requires ERK function, providing a link to TCR signaling. Together, these data indicate that regulation of glutamine use is an important component of T cell activation. Thus, a better understanding of glutamine sensing and use in T cells may reveal novel targets for immunomodulation.

Branched-chain amino acids and immunity

Although there has been great interest in the effects of amino acids on immune function, little is known about the impact of changes in BCAA availability on the ability of the immune system to function. Human immune cells incorporate BCAA into proteins and are able to oxidize BCAA. The immune system exists to protect the host from pathogenic invaders and from other noxious insults. Upon infection, there is a marked increase in demand for substrates by the immune system; these substrates provide energy and are the precursors for the synthesis of new cells, effector molecules, and protective molecules. Cell culture studies show that BCAA are absolutely essential for lymphocytes to synthesize protein, RNA, and DNA and to divide in response to stimulation. In mice, dietary BCAA restriction impairs several aspects of the immune function and increases the susceptibility to pathogens. Postsurgical or septic patients given BCAA intravenously showed improved immunity and this may relate to improved outcome. BCAAs are therefore absolutely essential for lymphocyte responsiveness and are necessary to support other immune cell functions. However, many aspects of BCAA and its effects on immune function have been understudied or not studied at all. More research is needed to understand the extent of the immune system's requirement for BCAA. It is likely that the essentiality of BCAA for the function of immune cells relates to protein synthesis.

Impact of fish oil enriched total parenteral nutrition on DNA synthesis, cytokine release and receptor expression by lymphocytes in the postoperative period

A prospective randomized study on sixty patients was conducted to investigate the effects of a fish oil containing total parenteral nutrition (TPN) regimen in the postoperative period on lymphocyte subset distribution, proliferation, cytokine production and interleukin-2 receptor (IL-2R) expression. Patients who underwent large bowel surgery were divided into three groups. Nineteen patients received TPN with fish oil (0.2 g/kg body weight per day) plus soybean oil (1.0 g/kg per day), twenty patients received soybean oil (1.2 g/kg per day), and twenty-one patients who were on a fat-free regimen served as the control group. Natural killer (NK) cells, total, B-, T-, T4-, T8-lymphocytes, proliferation of lymphocytes, in vitro production of IL-2, IFN-gamma, TNF-alpha, and IL-2R expression were measured. Fish oil administration did not affect subset distribution and proliferation of lymphocytes. Production of interleukin-2 (IL-2), interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) was augmented, and IL-2R expression less enhanced compared with the controls. It is concluded that administration of 0.2 g/kg per day fish oil after a moderate surgical stress is not immunosuppressive, but enhances the production of IFN-gamma, TNF-alpha and possibly IL-2.

Involvement of microglia in cerebrospinal fluid glutamate increase in SIV-infected rhesus monkeys (Macaca mulatta)

Cerebrospinal fluid (CSF) samples were collected from 24 uninfected and 24 SIV251 MPBMC-infected rhesus monkeys during early infection and from 6 animals in a longitudinal design up to 7 months postinfection to investigate excitatory and inhibitory amino acid neurotransmitter levels. During the early infection period CSF amino acid concentrations of infected animals were not significantly different from those of uninfected animals. However, long-term studies demonstrated that gamma-aminobutyric acid (GABA) concentrations were decreased while glutamate concentrations were increased late in infection compared with the preinfection values of the same animals. Moreover, we showed that the source of increased glutamate in animals with AIDS is, at least partially, microglial cells. Our data support the hypothesis that excitotoxicity is involved in immunodeficiency virus-induced neurological disease and propose microglia as a contributor to excitotoxic damage.

In vivo inter-organ protein metabolism of the splanchnic region and muscle during trauma, cancer and enteral nutrition

The study of protein kinetics has entered a new era by the recognition that whole body protein turnover only poorly reflects the true events occurring in several organs and with regard to the multitude of proteins present in the body. It is also increasingly recognized that the simultaneous synthesis and degradation of proteins is important in regulation and adaptation during several metabolic conditions like starvation, feeding, after trauma, and during exercise. Especially important is the recognition that the kinetics of individual proteins may change in opposite directions, thereby leading to fluxes of alpha-amino-nitrogen that serve to adapt to and survive a changing environment. At present, much emphasis is put upon molecular biological regulation. However, it is important that the metabolic processes that occur in the intact organism are still poorly defined. New technology allows the exploration of these processes, which should therefore prompt the initiation of further research in this area.

The influence of organic acids on the proliferation of human peripheral lymphocytes activated by concanavalin A and pokeweed mitogen

The present study was undertaken to assess the influence of 25 organic acids, which appear in high concentrations in tissues of patients with various organic acidaemias, on the proliferation of human peripheral lymphocytes stimulated with concanavalin A (Con A) (a T-cell activator) and pokeweed mitogen (PWM) (predominantly a B-cell activator). Mononuclear cells were cultivated in flat-bottomed 96-well microplates at 37 degrees C for 96 (Con A) or 144 h (PWM) in the presence of one mitogen at different concentrations and of one acid at doses ranging from 1 to 5 mM. Control cultures did not contain any acid. Cell reactivity was measured by the incorporation of tritiated thymidine into cellular DNA. We observed that, among the 25 acids tested, aminoadipic (AAD), 2-hydroxy-3-methylvaleric (HMV), 2-ketoisocaproic (KIC), 2-methylbutyric (MBA), propionic (PPA) and tiglic (TIG) acids strongly suppressed lymphocyte DNA synthesis in Con A-supplemented cultures, whereas in cultures stimulated with PWM, 2-ketoisovaleric (KIV) and PPA acids presented the same effect. In contrast, lactic (LAC) and pyruvic (PYR) acids activated lymphocyte DNA synthesis in cultures treated with Con A, the same effect occurring with LAC acid for PWM-stimulated lymphocytes. The most inhibitory or stimulatory acids were added to cultures at different times after the beginning of the incubation period when mitogens were added. Except for HMV, KIC, PPA and LAC acids, whose actions persisted even after 24 h from the beginning of culture, the others only exerted their effects when added at time zero. The present study therefore demonstrated that some organic acids modulate DNA synthesis in Con A- and PWM-stimulated human lymphocytes.

Excess glutamate in the cerebrospinal fluid in bacterial meningitis

We investigated possible neurotoxic components in the cerebrospinal fluid (CSF) of patients with bacterial meningitis. On murine cerebellar neuronal cell cultures, CSF exerted a dose-dependent toxic effect, which was attenuated by the NMDA receptor antagonist MK-801. Glutamate concentrations in the CSF of patients with bacterial meningitis were measured by an enzymatic assay and found to be significantly elevated (p < 0.001) as compared to viral meningitis and non-inflammatory neurological diseases. The concentration of glutamate in the CSF of patients with bacterial meningitis varied considerably and correlated with the severity of the disease as scored by the Glasgow Coma Scale. Cells in the CSF, mainly comprising polymorphonuclear granulocytes, did not release any glutamate into the culture medium, whereas blood monocytes produced remarkable amounts. These findings implicate an important role of monocytic inflammatory cells in bacterial meningitis by the release of glutamate, which may contribute to neuronal cell death.

The effect of organic acids on phytohaemagglutinin-activated proliferation of human lymphocytes in vitro

The present study assesses the effects of 25 organic acids on in vitro proliferation of human peripheral lymphocyte stimulated with phytohaemagglutinin (PHA). Lymphocytes were cultured in flat-bottomed 96-well microplates at 37 degrees C for 96 h in the presence of the mitogen and of one acid. The concentrations of organic acids tested in the cultures were from 1 to 5 mM, corresponding to those usually found in the blood of patients with organic acidaemias. Cellular growth was measured by the incorporation of 6[3H]-thymidine into cellular DNA. We observed that tiglic (2-methylcrotonic), alpha-keto-beta-methylvaleric, aminoadipic, sebacic and alpha-ketoisocaproic acids strongly inhibited lymphocyte DNA synthesis, whereas alpha-ketoisovaleric, propionic, alpha-hydroxy-beta-methylvaleric, alpha-methylbutyric and isobutyric acids moderately suppressed DNA synthesis. Lactic and ethylmalonic acids, however, stimulated DNA synthesis. The most inhibitory acids were added to cultures at different times after the beginning of the incubation period. Except for tiglic acid, whose action persisted even after 48 h from the onset of cultures, the others acted only when added during the first 24 h. The present study demonstrated that organic acids modulate DNA synthesis in mitogen-stimulated human lymphocytes.

The influence of amino acids on mitogen-activated proliferation of human lymphocytes in vitro

Recurrent infections are common features in patients affected by various aminoacidopathies. Since these disorders are biochemically characterized by tissue accumulation of amino acids, it is possible that these compounds may act as immunosuppressants. We therefore investigated the influence of 21 amino acids on in vitro cellular growth of lymphocytes stimulated with phytohaemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM), a recognized test of cellular immunocompetence. Human peripheral lymphocytes were cultured in flat-bottomed 96-well microplates at 37 degrees C for 96 (PHA and Con A) or 144 h (PWM) in the presence of one mitogen at different concentrations and of one amino acid added at doses of 2, 4 or 8 mM. Cell reactivity was measured by the incorporation of tritiated thymidine into cellular DNA and compared to that of identical cultures with no amino acids added (controls). We found that among the 21 amino acids tested, cysteine stimulated lymphocyte growth, whereas glutamate, tryptophan, phenylalanine and glutamine caused significant inhibition. These results may reflect an immunomodulatory role for some amino acids.

Cytokine production and DNA synthesis by human peripheral lymphocytes in response to palmitic, stearic, oleic, and linoleic acid

Effects of palmitic, stearic, oleic, and linoleic acid on mitogen-induced DNA synthesis, on production of IL-1 beta, IL-2, IFN-gamma, and TNF-alpha, and on IL-2R expression were determined in human peripheral lymphocytes. Free fatty acids (FFA) were added over a wide range of concentrations to cells cultured under serum free conditions with fatty acid free albumin. DNA synthesis was stimulated by low and inhibited by high FFA concentrations. Physiological concentrations were stimulatory, except for linoleic acid. Cytokine production became affected by all FFA tested. Palmitic acid enhanced the release of IFN-gamma at concentrations that diminished TNF-alpha production. Saturated fatty acids were significantly more potent than unsaturated fatty acids in affecting cytokine production. IFN-gamma secretion was significantly more stimulated or inhibited by the various FFA compared with the other cytokines. IL-2R expression correlated with the production of IL-2. When tested in combination, stimulatory as well as inhibitory effects of the individual FFA became attenuated. It is suggested that palmitic, stearic, oleic, and linoleic acid are physiological regulators of DNA synthesis and cytokine release in human peripheral lymphocytes. Modulation of FFA ratios may be an effective means for the fine tuning of the immune system. As secretory mechanisms of cytokines appear to exhibit substrate specificity for FFA, the release of individual cytokines may be selectively influenced by FFA.

ConA induced changes in energy metabolism of rat thymocytes

The influence of ConA on the energy metabolism of quiescent rat thymocytes was investigated by measuring the effects of inhibitors of protein synthesis, proteolysis, RNA/DNA synthesis, Na+K(+)-ATPase, Ca(2+)-ATPase and mitochondrial ATP synthesis on respiration. Only about 50% of the coupled oxygen consumption of quiescent thymocytes could be assigned to specific processes using two different media. Under these conditions the oxygen is mainly used to drive mitochondrial proton leak and to provide ATP for protein synthesis and cation transport, whereas oxygen consumption to provide ATP for RNA/DNA synthesis and ATP-dependent proteolysis was not measurable. The mitogen ConA produced a persistent increase in oxygen consumption by about 30% within seconds. After stimulation more than 80% of respiration could be assigned to specific processes. The major oxygen consuming processes of ConA-stimulated thymocytes are mitochondrial proton leak, protein synthesis and Na+K(+)-ATPase with about 20% each of total oxygen consumption, while Ca(2+)-ATPase and RNA/DNA synthesis contribute about 10% each. Quiescent thymocytes resemble resting hepatocytes in that most of the oxygen consumption remains unexplained. In contrast, the pattern of energy metabolism in stimulated thymocytes is similar to that described for Ehrlich Ascites tumour cells and splenocytes, which may also be in an activated state. Most of the oxygen consumption is accounted for, so the unexplained process(es) in unstimulated cells shut(s) off on stimulation.

ConA induced changes in energy metabolism of rat thymocytes

The influence of ConA on the energy metabolism of quiescent rat thymocytes was investigated by measuring the effects of inhibitors of protein synthesis, proteolysis, RNA/DNA synthesis, Na+K(+)-ATPase, Ca(2+)-ATPase and mitochondrial ATP synthesis on respiration. Only about 50% of the coupled oxygen consumption of quiescent thymocytes could be assigned to specific processes using two different media. Under these conditions the oxygen is mainly used to drive mitochondrial proton leak and to provide ATP for protein synthesis and cation transport, whereas oxygen consumption to provide ATP for RNA/DNA synthesis and ATP-dependent proteolysis was not measurable. The mitogen ConA produced a persistent increase in oxygen consumption by about 30% within seconds. After stimulation more than 80% of respiration could be assigned to specific processes. The major oxygen consuming processes of ConA-stimulated thymocytes are mitochondrial proton leak, protein synthesis and Na+K(+)-ATPase with about 20% each of total oxygen consumption, while Ca(2+)-ATPase and RNA/DNA synthesis contribute about 10% each. Quiescent thymocytes resemble resting hepatocytes in that most of the oxygen consumption remains unexplained. In contrast, the pattern of energy metabolism in stimulated thymocytes is similar to that described for Ehrlich Ascites tumour cells and splenocytes, which may also be in an activated state. Most of the oxygen consumption is accounted for, so the unexplained process(es) in unstimulated cells shut(s) off on stimulation.

Relationship between amino-acid metabolism and immune functions in human lymphocytes

Amino-acid degradation, interleukin-2 (IL-2) production, and DNA synthesis were analysed in concanavalin A (ConA)-treated peripheral venous lymphocytes from healthy blood donors and in lymphocytes from patients after uneventful abdominal surgery. ConA augmented (14)CO(2) production from (U-(14)C) glutamine (492 +/- 44 vs. 2274 +/- 174 pmol/10(6) cells x 40 min(-1)) while it had little effect on (14)CO(2) production from (1-(14)C) leucine (132 +/- 8 vs. 161 +/- 17 pmol/10(6) cells x 40 min(-1)) compared with the respective controls. Similar effects on amino-acid degradation were observed in response to surgery. Glutamine but not leucine amplified IL-2 production from ConA-treated cells, and it was a prerequisite for DNA synthesis. In lymphocytes from operated patients, spontaneous incorporation of ((3)H) thymidine was higher on day 3 and day 6 (310 and 2660 cpm/10(6) cells) after surgery, compared with the pre-operative day (68 cpm/10(6) cells; median values). These results indicate 1) that glutamine is more critical than leucine for the immune function of T-lymphocytes, and 2) that lymphocytes from patients undergoing uneventful abdomional surgery have become stimulated in vivo. It is suggested that these cells may qualify as a suitable experimental model to study the metabolic basis for immunologic functions after antigenic stimulation in vivo.

Characterization of glutamine transport into resting and concanavalin A-stimulated peripheral human lymphocytes

Characteristics of glutamine transport, its substrate specificity, and its pattern of competitive and non-competitive inhibition in response to amino acid analogues were determined in peripheral human lymphocytes, incubated with or without concanavalin A (Con A). Maximum capacity of transport (Vmax) at 37 degrees C and 136.9 mM Na+ was 30 pmol/10(6) cells/30 seconds, while the apparent Km was 142 microM. In cells exposed to 10 mM histidine, asparagine, serine, or leucine transport of glutamine declined to 28%, 15%, 17%, and 21%, respectively, of the rates in controls. Inhibition by histidine (Ki = 0.58 mM) and serine (Ki = 0.25 mM) was competitive, by leucine was non-competitive (Ki = 0.64), while alpha-methylamino-isobutyric acid and 2-amino carboxy-bicyclo (2.2.1)-heptane had no effect. In cells cultured for 24 hours with or without 10 micrograms/ml Con A, the apparent Km was 70 microM vs. 89 microM and Vmax 73 vs. 26 pmol/10(6) cells/30 seconds. Sodium depletion (9.0 mM NaCl) greatly diminished glutamine transport in resting and stimulated cells. Inhibition of glutamine transport by serine was sodium sensitive, while inhibition by histidine and asparagine was not. Serine had no competitive effect in sodium-depleted media. The data demonstrate what appear to be two carrier systems for glutamine, sodium sensitive and sodium insensitive. It is suggested that glutamine transport into lymphocytes occurs via processes similar to System N and System ASC described in other cells, with System ASC as the sodium-sensitive component. Con A augments the capacity rather than the affinity of glutamine transporting systems.