Glutamine in critical care:current evidence from systematic reviews

Glutamine, the most abundant amino acid in the body, is thought to become conditionally essential in critical illness. Some of the important roles for glutamine are as a carrier for inter-organ N, a preferred fuel for enterocytes and cells of the immune system, a substrate for renal NH3 formation and a precursor for glutathione. Mechanisms by which glutamine could improve recovery include attenuating oxidant damage and inflammatory cytokine production, reducing gut bacterial translocation and improving N balance. The present systematic review has found trends to suggest that parenteral and enteral glutamine supplementation reduce mortality, the development of infection and organ failure in critical illness. Trials of parenteral nutrition containing glutamine with patients after elective surgery also suggest reduction of infection, but it is unlikely that glutamine-containing parenteral nutrition would be used for such patients. The evidence base is limited by the quality of the reported trials and the suggestion that there is publication bias, with trials suggesting reduced infection being more likely to be published

Effect of the nitrogen source on glutamine and alanine biosynthesis in Neurospora crassa. An in vivo 15N nuclear magnetic resonance study

The influences of different nitrogen sources on the relative rates of biosynthesis of glutamine and alanine have been studied by 15N nuclear magnetic resonance spectroscopy of intact Neurospora crassa mycelia suspensions. The rate of glutamine synthesis was fastest after growth in media deficient in free ammonium ion, whereas it was slowest following growth in media containing both glutamic acid and glutamine. The reverse trend was observed for the biosynthesis of alanine. A competition between the two biosynthetic pathways for the same substrate, glutamic acid, was found to limit the rate of alanine synthesis when glutamine synthesis was rapid. The observed in vivo rates of these reactions are compared to the reported specific activities of the enzymes catalyzing the reactions, and implications of these results for nitrogen regulation of these pathways under various physiological conditions are discussed

Stable isotope metabolomics of pulmonary artery smooth muscle and endothelial cells in pulmonary hypertension and with TGF-beta treatment.

Altered metabolism in pulmonary artery smooth muscle cells (PASMCs) and endothelial cells (PAECs) contributes to the pathology of pulmonary hypertension (PH), but changes in substrate uptake and how substrates are utilized have not been fully characterized. We hypothesized stable isotope metabolomics would identify increased glucose, glutamine and fatty acid uptake and utilization in human PASMCs and PAECs from PH versus control specimens, and that TGF-β treatment would phenocopy these metabolic changes. We used 13C-labeled glucose, glutamine or a long-chain fatty acid mixture added to cell culture media, and mass spectrometry-based metabolomics to detect and quantify 13C-labeled metabolites. We found PH PASMCs had increased glucose uptake and utilization by glycolysis and the pentose shunt, but no changes in glutamine or fatty acid uptake or utilization. Diseased PAECs had increased proximate glycolysis pathway intermediates, less pentose shunt flux, increased anaplerosis from glutamine, and decreased fatty acid β-oxidation. TGF-β treatment increased glycolysis in PASMCs, but did not recapitulate the PAEC disease phenotype. In TGF-β-treated PASMCs, glucose, glutamine and fatty acids all contributed carbons to the TCA cycle. In conclusion, PASMCs and PAECs collected from PH subjects have significant changes in metabolite uptake and utilization, partially recapitulated by TGF-β treatment

Starve Cancer Cells of Glutamine: Break the Spell or Make a Hungry Monster?

Distinct from normal differentiated tissues, cancer cells reprogram nutrient uptake and utilization to accommodate their elevated demands for biosynthesis and energy production. A hallmark of these types of reprogramming is the increased utilization of, and dependency on glutamine, a nonessential amino acid, for cancer cell growth and survival. It is well-accepted that glutamine is a versatile biosynthetic substrate in cancer cells beyond its role as a proteinogenic amino acid. In addition, accumulating evidence suggests that glutamine metabolism is regulated by many factors, including tumor origin, oncogene/tumor suppressor status, epigenetic alternations and tumor microenvironment. However, despite the emerging understanding of why cancer cells depend on glutamine for growth and survival, the contribution of glutamine metabolism to tumor progression under physiological conditions is still under investigation, partially because the level of glutamine in the tumor environment is often found low. Since targeting glutamine acquisition and utilization has been proposed to be a new therapeutic strategy in cancer, it is central to understand how tumor cells respond and adapt to glutamine starvation for optimized therapeutic intervention. In this review, we first summarize the diverse usage of glutamine to support cancer cell growth and survival, and then focus our discussion on the influence of other nutrients on cancer cell adaptation to glutamine starvation as well as its implication in cancer therapy

Radiosynthesis, in vitro and preliminary in vivo evaluation of the novel glutamine derived PET tracers [18F]fluorophenylglutamine and [18F]fluorobiphenylglutamine

INTRODUCTION: Glucose has been deemed the driving force of tumor growth for decades. However, research has shown that several tumors metabolically shift towards glutaminolysis. The development of radiolabeled glutamine derivatives could be a useful molecular imaging tool for visualizing these tumors. We elaborated on the glutamine-derived PET tracers by developing two novel probes, namely [(18)F]fluorophenylglutamine and [(18)F]fluorobiphenylglutamine MATERIALS AND METHODS: Both tracers were labelled with fluorine-18 using our recently reported ruthenium-based direct aromatic fluorination method. Their affinity was evaluated with a [(3)H]glutamine inhibition experiment in a human PC-3 and a rat F98 cell line. The imaging potential of [(18)F]fluorophenylglutamine and [(18)F]fluorobiphenylglutamine was tested using a mouse PC-3 and a rat F98 tumor model. RESULTS: The radiosynthesis of both tracers was successful with overall non-decay corrected yields of 18.46 ± 4.18 % (n=10) ([(18)F]fluorophenylglutamine) and 8.05 ± 3.25 % (n=5) ([(18)F]fluorobiphenylglutamine). In vitro inhibition experiments showed a moderate and low affinity of fluorophenylglutamine and fluorobiphenylglutamine, respectively, towards the human ASCT-2 transporter. Both compounds had a low affinity towards the rat ASCT-2 transporter. These results were endorsed by the in vivo experiments with low uptake of both tracers in the F98 rat xenograft, low uptake of [(18)F]FBPG in the mice PC-3 xenograft and a moderate uptake of [(18)F]FPG in the PC-3 tumors. CONCLUSION: We investigated the imaging potential of two novel PET radiotracers [(18)F]FPG and [(18)F]FBPG. [(18)F]FPG is the first example of a glutamine radiotracer derivatized with a phenyl group which enables the exploration of further derivatization of the phenyl group to increase the affinity and imaging qualities. We hypothesize that increasing the affinity of [(18)F]FPG by optimizing the substituents of the arene ring can result in a high-quality glutamine-based PET radiotracer. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: We hereby report novel glutamine-based PET-tracers. These tracers are tagged on the arene group with fluorine-18, hereby preventing in vivo defluorination, which can occur with alkyl labelled tracers (e.g. (2S,4R)4-[(18)F]fluoroglutamine). [(18)F]FPG shows clear tumor uptake in vivo, has no in vivo defluorination and has a straightforward production. We believe this tracer is a good starting point for the development of a high-quality tracer which is useful for the clinical visualization of the glutamine transport

Ammonia assimilation in Bacillus polymyxa. 15N NMR and enzymatic studies

Pathways of ammonia assimilation into glutamic acid and alanine in Bacillus polymyxa were investigated by 15N NMR spectroscopy in combination with measurements of the specific activities of glutamate dehydrogenase, glutamine synthetase, glutamate synthetase, alanine dehydrogenase, and glutamic-alanine transaminase. Ammonia was found to be assimilated into glutamic acid predominantly by NADPH-dependent glutamate dehydrogenase with a Km of 2.9 mM for NH4+ not only in ammonia-grown cells but also in nitrate-grown and nitrogen-fixing cells in which the intracellular NH4+ concentrations were 11.2, 1.04, and 1.5 mM, respectively. In ammonia-grown cells, the specific activity of alanine dehydrogenase was higher than that of glutamic-alanine transaminase, but the glutamate dehydrogenase/glutamic-alanine transaminase pathway was found to be the major pathway of 15NH4+ assimilation into [15N]alanine. The in vitro specific activities of glutamate dehydrogenase and glutamine synthetase, which represent the rates of synthesis of glutamic acid and glutamine, respectively, in the presence of enzyme-saturating concentrations of substrates and coenzymes are compared with the in vivo rates of biosynthesis of [15N]glutamic acid and [alpha,gamma-15N]glutamine observed by NMR, and implications of the results for factors limiting the rates of their biosynthesis in ammonia- and nitrate-grown cells are discussed

Parenteral glutamine in critical illness : just what the gut needs

The role of glutamine as a metabolic fuel for the starving intestines, its capacity to limit bacterial translocation, lung sepsis and a pro-inflammatory cytokine response are reviewed in the context of uncertainities regarding current recommendations for glutamine supplementation in parenterally-fed critically ill patients. Weaknesses in the evidence-base showing benefit of intravenous glutamine supplementation are discussed together with aspects of glutamine supplementation via the enteral route.peer-reviewe

TP53-inducible Glycolysis and Apoptosis Regulator (TIGAR) Metabolically Reprograms Carcinoma and Stromal Cells in Breast Cancer.

A subgroup of breast cancers has several metabolic compartments. The mechanisms by which metabolic compartmentalization develop in tumors are poorly characterized. TP53 inducible glycolysis and apoptosis regulator (TIGAR) is a bisphosphatase that reduces glycolysis and is highly expressed in carcinoma cells in the majority of human breast cancers. Hence we set out to determine the effects of TIGAR expression on breast carcinoma and fibroblast glycolytic phenotype and tumor growth. The overexpression of this bisphosphatase in carcinoma cells induces expression of enzymes and transporters involved in the catabolism of lactate and glutamine. Carcinoma cells overexpressing TIGAR have higher oxygen consumption rates and ATP levels when exposed to glutamine, lactate, or the combination of glutamine and lactate. Coculture of TIGAR overexpressing carcinoma cells and fibroblasts compared with control cocultures induce more pronounced glycolytic differences between carcinoma and fibroblast cells. Carcinoma cells overexpressing TIGAR have reduced glucose uptake and lactate production. Conversely, fibroblasts in coculture with TIGAR overexpressing carcinoma cells induce HIF (hypoxia-inducible factor) activation with increased glucose uptake, increased 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3), and lactate dehydrogenase-A expression. We also studied the effect of this enzyme on tumor growth. TIGAR overexpression in carcinoma cells increases tumor growth in vivo with increased proliferation rates. However, a catalytically inactive variant of TIGAR did not induce tumor growth. Therefore, TIGAR expression in breast carcinoma cells promotes metabolic compartmentalization and tumor growth with a mitochondrial metabolic phenotype with lactate and glutamine catabolism. Targeting TIGAR warrants consideration as a potential therapy for breast cancer

Astrocyte glutamine synthetase : pivotal in health and disease

The multifunctional properties of astrocytes signify their importance in brain physiology and neurological function. In addition to defining the brain architecture, astrocytes are primary elements of brain ion, pH and neurotransmitter homoeostasis. GS (glutamine synthetase), which catalyses the ATP-dependent condensation of ammonia and glutamate to form glutamine, is an enzyme particularly found in astrocytes. GS plays a pivotal role in glutamate and glutamine homoeostasis, orchestrating astrocyte glutamate uptake/release and the glutamate-glutamine cycle. Furthermore, astrocytes bear the brunt of clearing ammonia in the brain, preventing neurotoxicity. The present review depicts the central function of astrocytes, concentrating on the importance of GS in glutamate/glutamine metabolism and ammonia detoxification in health and disease