A redox-responsive prodrug for tumor-targeted glutamine restriction

Modulating the metabolism of cancer cells, immune cells, or both is a promising strategy to potentiate cancer immunotherapy in the nutrient-competitive tumor microenvironment. Glutamine has emerged as an ideal target as cancer cells highly rely on glutamine for replenishing the tricarboxylic acid cycle in the process of aerobic glycolysis. However, non-specific glutamine restriction may induce adverse effects in unconcerned tissues and therefore glutamine inhibitors have achieved limited success in the clinic so far. Here we report the synthesis and evaluation of a redox-responsive prodrug of 6-Diazo-5-oxo-L-norleucine (redox-DON) for tumor-targeted glutamine inhibition. When applied to treat mice bearing subcutaneous CT26 mouse colon carcinoma, redox-DON exhibited equivalent antitumor efficacy but a greatly improved safety profile, particularly, in spleen and gastrointestinal tract, as compared to the state-of-the-art DON prodrug, JHU083. Furthermore, redox-DON synergized with checkpoint blockade antibodies leading to durable cures in tumor-bearing mice. Our results suggest that redox-DON is a safe and effective therapeutic for tumor-targeted glutamine inhibition showing promise for enhanced metabolic modulatory immunotherapy. The approach of reversible chemical modification may be generalized to other metabolic modulatory drugs that suffer from overt toxicity.

DON of Hope: Starving Pancreatic Cancer by Glutamine Antagonism

A promising approach to treat solid tumors involves disrupting their reliance on glutamine, a key component for various metabolic processes. Traditional attempts using glutamine inhibitors like 6-diazo-5-oxo-L-norleucine (DON) and CB-839 were unsuccessful, but new hope arises with DRP-104, a prodrug of DON. This compound effectively targets tumor metabolism while minimizing side effects. In a recent study published in Nature Cancer, Encarnación-Rosado and colleagues demonstrated in preclinical models that pancreatic ductal adenocarcinoma (PDAC) responds well to DRP-104, although tumors adapt through the MEK/ERK signaling pathway, which can be countered by the MEK inhibitor trametinib. In a related study, Recouvreux and colleagues found that DON is effective against pancreatic tumors, revealing that PDAC tumors upregulate asparagine synthesis in response to DON, making them susceptible to asparaginase treatment. Both studies underscore the potential of inhibiting glutamine metabolism and adaptive pathways as a promising strategy against PDAC. These findings pave the way for upcoming clinical trials utilizing DRP-104 and similar glutamine antagonists in the battle against solid tumors.

Differential Effects of Glutamine Inhibition Strategies on Antitumor CD8 T Cells

Activated T cells undergo metabolic reprogramming to meet anabolic, differentiation, and functional demands. Glutamine supports many processes in activated T cells, and inhibition of glutamine metabolism alters T cell function in autoimmune disease and cancer. Multiple glutamine-targeting molecules are under investigation, yet the precise mechanisms of glutamine-dependent CD8 T cell differentiation remain unclear. We show that distinct strategies of glutamine inhibition by glutaminase-specific inhibition with small molecule CB-839, pan-glutamine inhibition with 6-diazo-5-oxo-l-norleucine (DON), or by glutamine-depleted conditions (No Q) produce distinct metabolic differentiation trajectories in murine CD8 T cells. T cell activation with CB-839 treatment had a milder effect than did DON or No Q treatment. A key difference was that CB-839-treated cells compensated with increased glycolytic metabolism, whereas DON and No Q-treated cells increased oxidative metabolism. However, all glutamine treatment strategies elevated CD8 T cell dependence on glucose metabolism, and No Q treatment caused adaptation toward reduced glutamine dependence. DON treatment reduced histone modifications and numbers of persisting cells in adoptive transfer studies, but those T cells that remained could expand normally upon secondary Ag encounter. In contrast, No Q-treated cells persisted well yet demonstrated decreased secondary expansion. Consistent with reduced persistence, CD8 T cells activated in the presence of DON had reduced ability to control tumor growth and reduced tumor infiltration in adoptive cell therapy. Overall, each approach to inhibit glutamine metabolism confers distinct effects on CD8 T cells and highlights that targeting the same pathway in different ways can elicit opposing metabolic and functional outcomes.

Discovery of DRP-104, a tumor-targeted metabolic inhibitor prodrug

6-Diazo-5-oxo-l-norleucine (DON) is a glutamine antagonist that suppresses cancer cell metabolism but concurrently enhances the metabolic fitness of tumor CD8+ T cells. DON showed promising efficacy in clinical trials; however, its development was halted by dose-limiting gastrointestinal (GI) toxicities. Given its clinical potential, we designed DON peptide prodrugs and found DRP-104 [isopropyl(S)-2-((S)-2-acetamido-3-(1H-indol-3-yl)-propanamido)-6-diazo-5-oxo-hexanoate] that was preferentially bioactivated to DON in tumor while bioinactivated to an inert metabolite in GI tissues. In drug distribution studies, DRP-104 delivered a prodigious 11-fold greater exposure of DON to tumor versus GI tissues. DRP-104 affected multiple metabolic pathways in tumor, including decreased glutamine flux into the TCA cycle. In efficacy studies, both DRP-104 and DON caused complete tumor regression; however, DRP-104 had a markedly improved tolerability profile. DRP-104's effect was CD8+ T cell dependent and resulted in robust immunologic memory. DRP-104 represents a first-in-class prodrug with differential metabolism in target versus toxicity tissue. DRP-104 is now in clinical trials under the FDA Fast Track designation.

Mouse Model for Efficient Simultaneous Targeting of Glycolysis, Glutaminolysis, and De Novo Synthesis of Fatty Acids in Colon Cancer

Colon cancer is a highly anabolic entity with upregulation of glycolysis, glutaminolysis, and de novo synthesis of fatty acids, which also induces a hypercatabolic state in the patient. The blockade of either cancer anabolism or host catabolism has been previously proven to be a successful anticancer experimental treatment. However, it is still unclear whether the simultaneous blockade of both metabolic counterparts can limit malignant survival and the energetic consequences of such an approach. In this chapter, by using the CT26.WT murine colon adenocarcinoma cell line as a model of study, we provide a method to simultaneously perform a pharmacological blockade of tumor anabolism and host catabolism, as a feasible therapeutic approach to treat cancer, and to limit its energetic supply.

Targeting tumor-intrinsic hexosamine biosynthesis sensitizes pancreatic cancer to anti-PD1 therapy

Pancreatic ductal adenocarcinoma (PDAC) is considered to be a highly immunosuppressive and heterogenous neoplasm. Despite improved knowledge regarding the genetic background of the tumor and better understanding of the tumor microenvironment, immune checkpoint inhibitor therapy (targeting CTLA4, PD1, PDL1) has not been very successful against PDAC. The robust desmoplastic stroma, along with an extensive extracellular matrix (ECM) that is rich in hyaluronan, plays an integral role in this immune evasion. Hexosamine biosynthesis pathway (HBP), a shunt pathway of glycolysis, is a metabolic node in cancer cells that can promote survival pathways on the one hand and influence the hyaluronan synthesis in the ECM on the other. The rate-limiting enzyme of the pathway, glutamine-fructose amidotransferase 1 (GFAT1), uses glutamine and fructose 6-phosphate to eventually synthesize uridine diphosphate N-acetylglucosamine (UDP-GlcNAc). In the current manuscript, we targeted this glutamine-utilizing enzyme by a small molecule glutamine analog (6-diazo-5-oxo-l-norleucine [DON]). Our results showed that DON decreased the self-renewal potential and metastatic ability of tumor cells. Further, treatment with DON decreased hyaluronan and collagen in the tumor microenvironment, leading to an extensive remodeling of the ECM and an increased infiltration of CD8+ T cells. Additionally, treatment with DON sensitized pancreatic tumors to anti-PD1 therapy, resulting in tumor regression and prolonged survival.

Inhibition of glutamine metabolism accelerates resolution of acute lung injury

Despite recent advances, acute respiratory distress syndrome (ARDS) remains a severe and often fatal disease for which there is no therapy able to reduce the underlying excessive lung inflammation or enhance resolution of injury. Metabolic programming plays a critical role in regulating inflammatory responses. Due to their high metabolic needs, neutrophils, macrophages, and lymphocytes rely upon glutamine metabolism to support activation and function. Additionally, during times of physiologic stress, nearly all cells, including fibroblasts and epithelial cells, require glutamine metabolism. We hypothesized that inhibiting glutamine metabolism reduces lung inflammation and promotes resolution of acute lung injury. Lung injury was induced by instilling lipopolysaccharide (LPS) intratracheally. To inhibit glutamine metabolism, we administered a glutamine analogue, 6-diazo-5-oxo-L-norleucine (DON) that binds to glutamine-utilizing enzymes and transporters, after injury was well established. Treatment with DON led to less lung injury, fewer lung neutrophils, lung inflammatory and interstitial macrophages, and lower levels of proinflammatory cytokines and chemokines at 5 and/or 7 days after injury. Additionally, DON led to earlier expression of the growth factor amphiregulin and more rapid recovery of LPS-induced weight loss. Thus, DON reduced lung inflammation and promoted resolution of injury. These data contribute to our understanding of how glutamine metabolism regulates lung inflammation and repair, and identifies a novel target for future therapies for ARDS and other inflammatory lung diseases.

Glutaminase-1 stimulates the proliferation, migration, and survival of human endothelial cells

Glutaminase-1 (GLS1) is a mitochondrial enzyme found in endothelial cells (ECs) that metabolizes glutamine to glutamate and ammonia. Although glutaminolysis modulates the function of human umbilical vein ECs, it is not known whether these findings extend to human ECs beyond the fetal circulation. Furthermore, the molecular mechanism by which GLS1 regulates EC function is not defined. In this study, we show that the absence of glutamine in the culture media or the inhibition of GLS1 activity or expression blocked the proliferation and migration of ECs derived from the human umbilical vein, the human aorta, and the human microvasculature. GLS1 inhibition arrested ECs in the G0/G1 phase of the cell cycle and this was associated with a significant decline in cyclin A expression. Restoration of cyclin A expression via adenoviral-mediated gene transfer improved the proliferative, but not the migratory, response of GLS1-inhibited ECs. Glutamine deprivation or GLS1 inhibition also stimulated the production of reactive oxygen species and this was associated with a marked decline in heme oxygenase-1 (HO-1) expression. GLS1 inhibition also sensitized ECs to the cytotoxic effect of hydrogen peroxide and this was prevented by the overexpression of HO-1. In conclusion, the metabolism of glutamine by GLS1 promotes human EC proliferation, migration, and survival irrespective of the vascular source. While cyclin A contributes to the proliferative action of GLS1, HO-1 mediates its pro-survival effect. These results identify GLS1 as a promising therapeutic target in treating diseases associated with aberrant EC proliferation, migration, and viability.

Targeting metabolic abnormalities to reverse fibrosis in iatrogenic laryngotracheal stenosis

OBJECTIVE

Management of laryngotracheal stenosis (LTS) remains primarily surgical, with a critical need to identify targets for adjuvant therapy. Laryngotracheal stenosis scar fibroblasts exhibit a profibrotic phenotype with distinct metabolic shifts, including an increased glycolysis/oxidative phosphorylation ratio. This study examines the effects of the glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON) on collagen production, gene expression, proliferation, and metabolism of human LTS-derived fibroblasts in vitro.

METHOD

Paired normal and scar-derived fibroblasts isolated from subglottic and proximal tracheal tissue in patients with iatrogenic laryngotracheal stenosis (iLTS) were cultured. Proliferation rate, gene expression, protein production, and cellular metabolism were assessed in two conditions: 1) fibroblast growth medium, and 2) fibroblast growth medium with 1 × 10-4 M DON.

RESULTS

DON treatment reduced cellular proliferation rate (n = 7, P =  0.0150). Expression of genes collagen 1 and collagen 3 both were reduced (n = 7, P =  0.0102, 0.0143, respectively). Soluble collagen production decreased (n = 7, P =  0.0056). As measured by the rate of extracellular acidification, glycolysis and glycolytic capacity decreased (n = 7, P =  0.0082, 0.0003, respectively). adenosine triphosphate (ATP) production and basal respiration decreased (n = 7, P = 0.0045, 0.0258, respectively), determined by measuring the cellular rate of oxygen consumption.

CONCLUSION

The glutamine antagonist DON reverses profibrotic changes by inhibiting both glycolysis and oxidative phosphorylation in iLTS scar fibroblasts. In contrast to untreated iLTS scar fibroblasts, collagen gene expression, protein production, metabolic rate, and proliferation were significantly reduced. These results suggest DON and/or its derivatives as strong candidates for adjuvant therapy in the management of iatrogenic laryngotracheal stenosis. Enzymes involved in glutamine metabolism inhibited by DON offer targets for future investigation.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:E59-E67, 2018.

Antagonizing Bcl-2 family members sensitizes neuroblastoma and Ewing's sarcoma to an inhibitor of glutamine metabolism

Neuroblastomas (NBL) and Ewing’s sarcomas (EWS) together cause 18% of all pediatric cancer deaths. Though there is growing interest in targeting the dysregulated metabolism of cancer as a therapeutic strategy, this approach has not been fully examined in NBL and EWS. In this study, we first tested a panel of metabolic inhibitors and identified the glutamine antagonist 6-diazo-5-oxo-L-norleucine (DON) as the most potent chemotherapeutic across all NBL and EWS cell lines tested. Myc, a master regulator of metabolism, is commonly overexpressed in both of these pediatric malignancies and recent studies have established that Myc causes cancer cells to become “addicted” to glutamine. We found DON strongly inhibited tumor growth of multiple tumor lines in mouse xenograft models. In vitro, inhibition of caspases partially reversed the effects of DON in high Myc expressing cell lines, but not in low Myc expressing lines. We further showed that induction of apoptosis by DON in Myc-overexpressing cancers is via the pro-apoptotic factor Bax. To relieve inhibition of Bax, we tested DON in combination with the Bcl-2 family antagonist navitoclax (ABT-263). In vitro, this combination caused an increase in DON activity across the entire panel of cell lines tested, with synergistic effects in two of the N-Myc amplified neuroblastoma cell lines. Our study supports targeting glutamine metabolism to treat Myc overexpressing cancers, such as NBL and EWS, particularly in combination with Bcl-2 family antagonists.

Peripheral inhibition of glutaminase reduces carrageenan-induced Fos expression in the superficial dorsal horn of the rat

In inflamed tissue, the levels of the excitatory amino acid glutamate are increased. Glutamate sensitizes peripheral axons of primary afferent neurons during inflammation leading to decreased firing threshold and hyperexcitability. One proposed source of glutamate is the primary afferent. Antagonizing glutamate receptors on peripheral axons of primary afferents during inflammation provides analgesia in animals and humans. The enzyme glutaminase is used by primary sensory neurons to convert glutamine to glutamate, and peripheral inhibition of glutaminase with 6-diazo-5-oxo-l-norleucine (DON) provides long-lasting analgesia during inflammation. In this study, we measured the effects of glutaminase inhibition on carrageenan-induced spinal Fos expression. Rats were given intraplantar injections of carrageenan and treated locally with either vehicle or DON. After 3h of inflammation, hind paw swelling and spinal expression of Fos were examined. CellProfiler was used to automate Fos nuclei counting in five laminar groupings in the spinal cord (I-II, III-IV, V-VI, VII-IX, X). Carrageenan increased hind paw thickness by approximately 70% and spinal Fos expression in superficial (I-II) and deep (V-VI) laminae by 10-fold and 5-fold, respectively. Treatment with DON reduced hind paw swelling by approximately 13% and suppressed Fos expression in the laminae I-II by approximately 54%, but not the deep laminae. Our results further support the notion of glutamate as a peripheral inflammatory mediator and indicate that glutaminase should be considered as a novel therapeutic target for treatment of inflammatory pain.

[Isolation of Pseudomonas aurantiaca strains capable of overproduction of phenazine antibiotics]

N-methyl-N'-nitro-N-nitrosoguanidine (NH)-induced mutagenesis with subsequent selection for resistance to toxic amino acid analogues (azaserine, m-fluoro-DL-phenylalanine, and 6-diazo-5-oxo-L-norleucine) was applied to Pseudomonas aurantiaca B-162. The resulting strains produced phenazine antibiotics three times more efficiently than the wild type strain and ten times more efficiently than the known pseudomonad strains. Overproduction of phenazine antibiotics was shown to result either from deregulation of 3-deoxi-D-arabinohepulosonate-7-phosphate synthase (DAHP synthase), the key enzyme of the aromatic pathway (removal of inhibition by phenylalanine, tyrosine, and phenazine), or overproduction of N-hexanoyl homoserine lactone, the regulatory molecule of positive control of cellular metabolism (QS system).

Influence of hyaluronic acid synthesis and cumulus mucification on bovine oocyte in vitro maturation, fertilisation and embryo development

During cumulus-oocyte complex (COC) maturation, cumulus expansion involves the deposition of mucoelastic compounds, especially hyaluronic acid, synthesised from glucose via the hexosamine biosynthesis pathway. The aim of the present study was to determine the effects of uridine monophosphate (UMP) and 6-diazo-5-oxo-L-norleucine (DON), inhibitors of hyaluronic acid synthesis, during bovine oocyte in vitro maturation (IVM) on cumulus expansion, glucose uptake, protein synthesis, cumulus cell number, meiotic maturation, cleavage rate and subsequent embryo development. A further aim of the study was to examine the effect of hyaluronic acid on sperm capacitation and acrosome reaction in relation to the capacity of COCs to be fertilised in vitro. A low correlation between glucose uptake and degree of cumulus expansion was observed. Total and partial inhibition of cumulus expansion was observed with DON and UMP, respectively, and was accompanied by a decrease in glucose uptake with DON. Total protein content and cumulus cell number per COC increased during IVM, but was unaffected by the presence of DON or UMP, as was oocyte meiotic maturation. Rates of cleavage and blastocyst development decreased in oocytes matured with DON and UMP, although this inhibition was reversed when the in vitro fertilisation (IVF) medium contained heparin. Hyaluronic acid induced capacitation and the acrosome reaction, and in IVF medium prevented the inhibition of cleavage and blastocyst development by DON in a similar fashion to heparin. Hyaluronic acid synthesis during cumulus mucification contributes to the penetration and fertilisation of bovine oocytes, most likely by facilitating the processes of capacitation and acrosome reaction. Mucification during IVM is independent of cumulus cell proliferation, COC protein content, oocyte meiotic maturation and subsequent developmental competence once fertilised.

Which mechanisms are involved in taurine-dependent granulocytic immune response or amino- and α-keto acid homeostasis?

We examined the effects of beta-alanine (taurine analogue and taurine transport antagonist), taurine (regarding its role in neutrophil (PMN) immunonutrition) and taurine combined either with L-NAME (inhibitor of *NO-synthase), SNAP (*NO donor), DON (glutamine-analogue and inhibitor of glutamine-requiring enzymes), DFMO (inhibitor of ornithine-decarboxylase) and beta-alanine on neutrophil amino- and alpha-keto acid profiles or important PMN immune functions in order to establish whether taurine transport-, nitric oxide-, glutamine- or ornithine-dependent mechanisms are involved in any of the taurine-induced effects. According to the present findings, the taurine-mediated effect appears to be based primarily on a modulation of important transmembraneous transport mechanisms and only secondarily on directly or indirectly induced modifications in intragranulocytic amino- and alpha-keto acid homoeostasis or metabolism. Although a direct relation to the parallel observed immunological modifications can only be presumed, these results show very clearly that compositional modifications in the free intragranulocytic amino- and alpha keto-acid pools coinciding with changes in intragranulocytic taurine levels are relevant metabolic determinants that can significantly influence the magnitude and quality of the granulocytic immune response.

Glutamine in the mechanism of ammonia-induced astrocyte swelling

Brain edema and the subsequent increase in intracranial pressure are the major neurological complications in fulminant hepatic failure (FHF). Brain edema in FHF is predominantly "cytotoxic" due principally to astrocyte swelling. It is generally believed that ammonia plays a key role in this process, although the mechanism by which ammonia brings about such swelling is yet to be defined. It has been postulated that glutamine accumulation in astrocytes subsequent to ammonia detoxification results in increased osmotic forces leading to cell swelling. While the hypothesis is plausible and has gained support, it has never been critically tested. In this study, we examined whether a correlation exists between cellular glutamine levels and the degree of cell swelling in cultured astrocytes exposed to ammonia. Cultured astrocytes derived from rat brain cortices were exposed to ammonia (5 mM) for different time periods and cell swelling was measured. Cultures treated with ammonia for 1-3 days showed a progressive increase in astrocyte cell volume (59-127%). Parallel treatment of astrocyte cultures with ammonia showed a significant increase in cellular glutamine content (60-80%) only at 1-4 h, a time when swelling was absent, while glutamine levels were normal at 1-3 days, a time when peak cell swelling was observed. Thus no direct correlation between cell swelling and glutamine levels was detected. Additionally, acute increase in intracellular levels of glutamine by treatment with the glutaminase inhibitor 6-diazo-5-oxo-L-norleucine (DON) after ammonia exposure also did not result in swelling. On the contrary, DON treatment significantly blocked (66%) ammonia-induced astrocyte swelling at a later time point (24 h), suggesting that some process resulting from glutamine metabolism is responsible for astrocyte swelling. Additionally, ammonia-induced free radical production and induction of the mitochondrial permeability transition (MPT) were significantly blocked by treatment with DON, suggesting a key role of glutamine in the ammonia-induced free radical generation and the MPT. In summary, our findings indicate a lack of direct correlation between the extent of cell swelling and cellular levels of glutamine. While glutamine may not be acting as an osmolyte, we propose that glutamine-mediated oxidative stress and/or the MPT may be responsible for the astrocyte swelling by ammonia.

Differential response of glutamine in cultured neurons and astrocytes

Glutamine, a byproduct of ammonia detoxification, is found elevated in brain in hepatic encephalopathy (HE) and other hyperammonemic disorders. Such elevation has been implicated in some of the deleterious effects of ammonia on the central nervous system (CNS). Recent studies have shown that glutamine results in the induction of the mitochondrial permeability transition (MPT) in cultured astrocytes. We examined whether glutamine shows similar effects in cultured neurons. Both cultured astrocytes and neurons were exposed to glutamine (6.5 mM) for 24 hr and the MPT was assessed by changes in cyclosporin A (CsA)-sensitive inner mitochondrial membrane potential (DeltaPsi(m)) using the potentiometric dye tetramethylrhodamine ethyl ester (TMRE). Glutamine significantly dissipated the DeltaPsi(m) in astrocytes as demonstrated by a decrease in mitochondrial TMRE fluorescence, a process that was blocked by CsA. On the other hand, treatment of cultured neurons with glutamine had no effect on the DeltaPsi(m). Dissipation of the DeltaPsi(m) in astrocytes by glutamine was blocked by treatment with 6-diazo-5-oxo-L-norleucine (DON; 100 microM), suggesting that glutamine hydrolysis and the subsequent generation of ammonia, which has been shown previously to induce the MPT, might be involved in MPT induction by glutamine. These data indicate that astrocytes but not neurons are vulnerable to the toxic effects of glutamine. The selective induction of oxidative stress and the MPT by glutamine in astrocytes may partially explain the deleterious affects of glutamine on the CNS in the setting of hyperammonemia, as well as account for the predominant involvement of astrocytes in the pathogenesis of HE and other hyperammonemic conditions.

Modulation of tumor induced angiogenesis in Ehrlich ascites tumor

In this study the enzyme glutaminase, purified from the ascites fluid of ovarian cancer patients, was analysed for its antiangiogenic activity. Intraperitoneal administration of this enzyme reduces the number of tumor directed capillaries in solid and ascites tumor bearing Swiss mice induced by transplantation of Ehrlich ascites cells. The enzyme has a critical role in regulating the secretion of vascular endothelial growth factor (VEGF) from tumor cell and in turn tumor growth. Glutamine analogue like 6-diazo, 5- oxo L-norleucine (DON) is also found to be effective in regulating vascular endothelial growth factor (VEGF) secretion from tumor cells in vitro. Treatment with enzyme reduced serum VEGF levels of the tumor induced animals. In vitro VEGF production by EAC cells was reduced in a concentration dependent manner in presence of glutamine analogue.

Characterization of the products of the genes SNO1 and SNZ1 involved in pyridoxine synthesis in Saccharomyces cerevisiae

Genes SNO1 and SNZ1 are Saccharomyces cerevisiae homologues of PDX2 and PDX1 which participate in pyridoxine synthesis in the fungus Cercospora nicotianae. In order to clarify their function, the two genes SNO1 and SNZ1 were expressed in Escherichia coli either individually or simultaneously and with or without a His-tag. When expressed simultaneously, the two protein products formed a complex and showed glutaminase activity. When purified to homogeneity, the complex exhibited a specific activity of 480 nmol.mg(-1).min(-1) as glutaminase, with a Km of 3.4 mm for glutamine. These values are comparable to those for other glutamine amidotransferases. In addition, the glutaminase activity was impaired by 6-diazo-5-oxo-L-norleucine in a time- and dose-dependent manner and the enzyme was protected from deactivation by glutamine. These data suggest strongly that the complex of Sno1p and Snz1p is a glutamine amidotransferase with the former serving as the glutaminase, although the activity was barely detectable with Sno1p alone. The function of Snz1p and the amido acceptor for ammonia remain to be identified.

High glucose stimulates angiotensinogen gene expression and cell hypertrophy via activation of the hexosamine biosynthesis pathway in rat kidney proximal tubular cells

The present study investigated whether activation of the hexosamine biosynthesis pathway might mediate at least in part the high glucose effect on angiotensinogen (ANG) gene expression and immortalized renal proximal tubular cell (IRPTC) hypertrophy. IRPTC were cultured in monolayer. ANG, renin, and beta-actin mRNA expression were determined by specific RT-PCR assays. Phosphorylation of p38 MAPK, activating transcription factor-2 (ATF-2), and cAMP-responsive element-binding protein (CREB) was determined by Western blot analysis. Cell hypertrophy was assessed by flow cytometry, intracellular p27kip1 protein levels, and [3H]leucine incorporation into proteins. Glucosamine stimulated ANG and renin mRNA expression and enhanced p38 MAPK, ATF-2, and CREB phosphorylation in normal glucose (5 mm) medium. Azaserine and 6-diazo-5-oxo-l-norleucine (inhibitors of glutamine: fructose-6-phosphate amino transferase enzyme) blocked the stimulatory effect of high glucose, but not that of glucosamine, on ANG gene expression in IRPTCs. SB 203580 (a specific p38 MAPK inhibitor) attenuated glucosamine action on ANG gene expression as well as p38 MAPK and ATF-2 phosphorylation, but not that of CREB. GF 109203X and calphostin C (inhibitors of protein kinase C) blocked the effect of glucosamine on ANG gene expression and CREB phosphorylation, but had no impact on p38 MAPK and ATF-2 phosphorylation. Finally, both glucosamine and high glucose induced IRPTC hypertrophy. The hypertrophic effect of glucosamine was blocked in the presence of GF 109203X, but not azaserine and SB 203580. In contrast, the hypertrophic effect of high glucose was blocked in the presence of azaserine and GF 109203X, but not SB203580. Our studies demonstrate that the stimulatory effect of high glucose on ANG gene expression and IRPTC hypertrophy may be mediated at least in part via activation of hexosamine biosynthesis pathway signaling.

Role of acetyl-L-carnitine in the brain: revealed by Bioradiography

To elucidate the role of acetyl-L-carnitine in the brain, we used a novel method, 'Bioradiography,' in which the dynamic process could be followed in living slices by use of positron-emitter labeled compounds and imaging plates. We studied the incorporation of 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) into rat brain slices incubated in oxygenated Krebs-Ringer solution. Under the glucose-free condition, [18F]FDG uptake rate decreased with time and plateaued within 350 min in the cerebral cortex and cerebellum, and the addition of 1 or 5mM acetyl-L-carnitine did not alter the [18F]FDG uptake rate. When a glutaminase inhibitor, 0.5mM 6-diazo-5-oxo-L-norleucine (DON), was added under the normal glucose condition, [18F]FDG uptake rate decreased. Acetyl-L-carnitine (1mM), which decreased [18F]FDG uptake rate, reversed this DON-induced decrease in [18F]FDG uptake rate in the cerebral cortex. These results suggest that acetyl-L-carnitine can be used for the production of releasable glutamate rather than as an energy source in the brain.

Glutamine delays spontaneous apoptosis in neutrophils

Nuclear, mitochondrial, and plasma membrane events associated with apoptosis were investigated in rat neutrophils cultivated for 3, 24, and 48 h in the absence or presence of glutamine (0.5, 1.0, and 2.0 mM). Condensation of chromatin was reduced after 24 or 48 h of culture in the presence of glutamine compared with its absence as assessed by Hoechst 33342 staining. The level of Escherichia coli phagocytosis in the presence of glutamine was markedly increased compared with the level achieved by cells cultured in the absence of glutamine. Annexin V binding to externalized phosphatidylserine was reduced in the presence of glutamine. Sensitive fluorochrome rhodamine 123, as determined by fluorescence-activated cell sorting and confocal microscopy, was used to monitor loss of the mitochondrial transmembrane potential. In the absence of glutamine, neutrophils exhibited a marked reduction in the uptake of rhodamine 123. In the presence of 1.0 or 2.0 mM glutamine, the uptake of rhodamine was 20 or 38% higher, respectively. Similar effect was found in human neutrophils by measuring DNA fragmentation and mitochondrial transmembrane potential. Therefore, glutamine protects from events associated with triggering and executing apoptosis in both rat and human neutrophils.

Effect of gamma-glutamyl transpeptidase inhibitors on the transport of glutamate into neuronal and glial primary cultures

Inhibitors of gamma-glutamyl transpeptidase (mixture of serine and borate--13 mM, kainic acid--5 mM and 6-diazo-5-oxo-L-norleucine--2 mM) significantly suppressed glutamate uptake into cultured neurones and glial cells. The simultaneous application of any of these inhibitors with ouabain resulted in a further decline in glutamate uptake. It can be speculated that gamma-glutamyl transpeptidase significantly contributes to glutamate transport into nerve cells in the early period of brain development until the Na(+)-K(+)-gradient is fully constituted.

Design, synthesis, and evaluation of gluten peptide analogs as selective inhibitors of human tissue transglutaminase

Recent studies have implicated a crucial role for tissue transglutaminase (TG2) in the pathogenesis of Celiac Sprue, a disorder of the small intestine triggered in genetically susceptible individuals by dietary exposure to gluten. Proteolytically stable peptide inhibitors of human TG2 were designed containing acivicin or alternatively 6-diazo-5-oxo-norleucine (DON) as warheads. In biochemical and cell-based assays, the best of these inhibitors, Ac-PQP-(DON)-LPF-NH(2), was considerably more potent and selective than other TG2 inhibitors reported to date. Selective pharmacological inhibition of extracellular TG2 should be useful in exploring the mechanistic implications of TG2-catalyzed modification of dietary gluten, a phenomenon of considerable relevance in Celiac Sprue.

A molecular warhead and its target: tissue transglutaminase and Celiac Sprue

The substitution of a glutamine residue with 6-diazo-5-oxo-norleucine (DON) transforms an immunodominant gluten peptide into a potent inhibitor of tissue transglutaminase. DON-modified peptides could be useful for the study and therapy of celiac sprue.

Hexosamines regulate leptin production in 3T3-L1 adipocytes through transcriptional mechanisms

This study was undertaken to examine the regulation of leptin gene (LEP) transcription and leptin release by hexosamines in 3T3-L1 adipocytes. Glucosamine (1 mM), an intermediate in hexosamine biosynthesis, increased leptin release to 117.0 +/- 7.3% (P = 0.0430; n = 9) and 134.6 +/- 6.5% of the control value (P = 0.0367; n = 4) by 48 and 96 h, respectively. With 0.01 mM glucosamine, leptin release was increased to 120.0 +/- 3.0% of the control value (P = 0.0069; n = 4) by 96 h of treatment. Glucose at 5 and 20 mM stimulated leptin release to 759 +/- 227% and 1104 +/- 316% of the control value over the 96-h culture period. Inhibition of hexosamine biosynthesis with 6-diazo-5-oxonorleucine (20 microM) reduced glucose-stimulated leptin release 13 +/- 2.3% and 29.9 +/- 6.6% at 24 and 96 h, respectively (n = 4; P < 0.05). A 24-h incubation in 5 mM glucose significantly increased (163.0 +/- 19.3%; n = 7) the activity of a human LEP promoter electroporated into differentiated 3T3-L1 cells. Glucosamine (1 mM; 48 h) also increased LEP promoter activity 170.0 +/- 13.0% (n = 5). Mutation of the three Sp1 binding sites in the LEP construct significantly reduced promoter activity. However, glucose (5 mM; 24 h) and glucosamine (1 mM; 48 h) increased the activity of the mutated promoter to 165 +/- 40% (n = 8) and 143 +/- 13% of the control value (n = 8). Glucosamine significantly increased O-glycosylation of Sp1 by 16.1 +/- 4.5% (P = 0.0305; n = 3). These data demonstrate that glucose and hexosamines regulate leptin production through transcriptional mechanisms localized to the proximal portion of the LEP promoter. Hexosamine-mediated regulation of LEP gene expression does not depend on Sp1 binding to traditional sites on the promoter.

Trypanosoma brucei CTP synthetase: a target for the treatment of African sleeping sickness

The drugs in clinical use against African sleeping sickness are toxic, costly, or inefficient. We show that Trypanosoma brucei, which causes this disease, has very low levels of CTP, which are due to a limited capacity for de novo synthesis and the lack of salvage pathways. The CTP synthetase inhibitors 6-diazo-5-oxo-l-norleucine (DON) and alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (acivicin) reduced the parasite CTP levels even further and inhibited trypanosome proliferation in vitro and in T. brucei-infected mice. In mammalian cells, DON mainly inhibits de novo purine biosynthesis, a pathway lacking in trypanosomes. We could rescue DON-treated human and mouse fibroblasts by the addition of the purine base hypoxanthine to the growth medium. For treatment of sleeping sickness, we propose the use of CTP synthetase inhibitors alone or in combination with appropriate nucleosides or bases.

Inhibition of Escherichia coli glucosamine synthetase by novel electrophilic analogues of glutamine--comparison with 6-diazo-5-oxo-norleucine

A series of electrophilic glutamine analogues based on 6-diazo-5-oxo-norleucine has been prepared, using novel synthetic routes, and evaluated as inhibitors of Escherichia coli glucosamine synthetase. The gamma-dimethylsulphonium salt analogue of glutamine was found to be one of the most potent inactivators of this enzyme yet reported, with an apparent second order rate constant (k2/Ki) of 3.5 x 10(5) M(-1) min(-1).

Hexosamines regulate leptin production in human subcutaneous adipocytes

The hexosamine biosynthetic pathway has recently been proposed as a mechanism through which cells "sense" nutrient flux to regulate leptin release. This study was undertaken to examine the regulation of leptin production by hexosamines in human adipocytes. Adipose tissue UDP-N-acetylglucosamine, an end product of hexosamine biosynthesis, was elevated 3.2-fold, and ob messenger ribonucleic acid was elevated 2-fold in the sc adipose tissue of 17 obese [body mass index (BMI), 41.3+/-12.0 kg/m2; age, 31+/-5 yr] subjects compared to 14 lean (BMI, 23.4+/-1.6 kg/m2; age, 33+/-11 yr) subjects. Serum leptin was increased 2.7-fold in the obese subjects. A significant positive relationship was found between adipose tissue UDP-N-acetylglucosamine and BMI (Spearman correlation = 0.576; P = 0.0007) and between UDP-N-acetylglucosamine and serum leptin (Spearman correlation = 0.4650; P = 0.0145). Treatment of isolated sc adipocytes with 1 mmol/L glucosamine, an intermediate product in UDP-N-acetylglucosamine biosynthesis, increased leptin release 21.4+/-17.6% (mean +/- SD) over control (P = 0.0365) and 74.5+/-82.8% over control (P = 0.0271) in adipocytes from lean (BMI, 23.2+/-1.6 kg/m2; n = 6) and obese (BMI, 55.4+/-13.0 kg/m2,; n = 9) subjects, respectively, by 48 h of culture. Inhibition of UDP-N-acetylglucosamine biosynthesis with 6-diazo-5-oxo-norleucine reduced glucose-stimulated leptin release from cultured adipocytes 21.8+/-32.4% (P = 0.0395; n = 12) and ob gene expression 19.9+/-18.9% (P = 0.0208; n = 8) by 48 h of treatment. These findings suggest that hexosamine biosynthesis regulates leptin production in human adipose tissue.

Hyaluronic acid as an anti-angiogenic shield in the preovulatory rat follicle

Angiogenesis in the preovulatory follicle is confined to the theca cell layers, and penetration of capillaries through the basement membrane into the granulosa cell layers does not occur until after ovulation. However, elevated expression of the angiogenic growth factor (VEGF) has been reported in the cumulus cells surrounding the oocyte, which are expelled from the follicle during ovulation. This spatial and temporal discrepancy between VEGF expression and angiogenesis was studied here in the rat ovarian follicle, and we showed that cumulus cells secrete to the follicular fluid, in addition to VEGF, material with antiangiogenic activity that blocks endothelial cell proliferation, migration, and capillary formation in vitro. Hyaluronic acid produced by the cumulus cells can account for this antiangiogenic activity. Degradation of hyaluronic acid by hyaluronidase restored proliferation and migration of endothelial cells directed toward the cumulus. Inhibition of hyaluronic acid synthesis with 6-diazo-5-oxo-1-norleucine restored endothelial proliferation and migration in vitro, and it also resulted in early penetration of capillaries across the follicular basement membrane in vivo. These results support the role of hyaluronic acid produced by the cumulus cells as a high-molecular-weight, antiangiogenic shield that prevents premature vascularization of the preovulatory follicle by blocking endothelial cell migration and proliferation.

Glutamine metabolism in endothelial cells: ornithine synthesis from glutamine via pyrroline-5-carboxylate synthase

L-Glutamine (the most abundant free amino acid in plasma and the body) is a potent inhibitor of endothelial NO synthesis. However, little is known about glutamine metabolism in endothelial cells (EC). As an initial step toward understanding the role of glutamine in endothelial physiology, the present study was conducted to quantify glutamine catabolism in microvascular, aortic and venous EC. For metabolic studies, EC were incubated for 1 h in Krebs bicarbonate buffer containing 5 mM glucose and 0.5-4 mM L-[U-(14)C]-glutamine. For enzymological studies, cell extracts and mitochondrial fractions were prepared to determine the activities of glutamine-degrading enzymes. Our results reveal extensive hydrolysis of glutamine to glutamate and ammonia in a concentration-dependent manner via phosphate-dependent glutaminase in all EC studied. In addition, both metabolic and enzymological evidence indicate a novel pathway for endothelial synthesis of ornithine from glutamine via pyrroline-5-carboxylate synthase. This new knowledge of glutamine metabolism may pave a new path for understanding the physiological role of glutamine in vascular function.

Glucosamine activates the plasminogen activator inhibitor 1 gene promoter through Sp1 DNA binding sites in glomerular mesangial cells

Increased flux through the hexosamine biosynthetic pathway is associated with altered gene expression. To investigate the underlying mechanisms, we treated glomerular mesangial cells with glucosamine and studied the regulation of the plasminogen activator inhibitor (PAI)-1 gene. Incubating mesangial cells with 2 mmol/l glucosamine for 4 days resulted in a 3.1+/-0.4-fold increase in PAI-1 mRNA levels (P < 0.01) and a 33+/-9-fold increase in the activity of a transiently transfected PAI-1 promoter-luciferase reporter gene (P < 0.01). Cotransfection of an expression vector for a dominant-negative type II TGF-beta receptor with the PAI-1 promoter-reporter gene did not interfere with this effect of glucosamine. However, mutation of 2 putative Sp1 sites in the PAI-1 promoter, at -76 to -71 and -44 to -39, markedly reduced induction of PAI-1 luciferase activity by glucosamine, from 8.9+/-1.9-fold to 1.7+/-0.5-fold (P < 0.01). An electrophoretic mobility shift assay demonstrated that glucosamine increased Sp1 DNA binding by 31+/-11% (P < 0.05), implying that the effects of glucosamine were explained, in part, by changes in Sp1 DNA binding. High glucose (20 mmol/l) also activated the transiently transfected PAI-1 promoter (2.5+/-0.4-fold). This effect was diminished by mutation of both the PAI-1 promoter Sp1 sites (1.2+/-0.3-fold, P < 0.05). In addition, 6-diazo-5-oxo-L-norleucine, a glutamine:fructose-6-phosphate-amidotransferase inhibitor, blocked the induction by high glucose (4.7+/-0.8- to 0.9+/-0.1-fold, P < 0.01). These results indicate that stimulation of the PAI-1 promoter by both high glucose and glucosamine involves Sp1 and that the hexosamine pathway may be involved in the regulation of gene expression by high glucose in glomerular mesangial cells.

Stimulation by eicosapentaenoic acids of leptin mRNA expression and its secretion in mouse 3T3-L1 adipocytes in vitro

Recent evidence indicates that both leptin and eicosapentaenoic acids (EPA) improve insulin sensitivity. In the present study, we examined the effect of EPA on endogenous leptin expression in 3T3-L1 adipocytes to clarify whether the EPA's effect is exerted through leptin expression. EPA caused a time- and dose-dependent increase of leptin mRNA levels in 3T3-L1 adipocytes. Leptin mRNA expression was significantly increased up to 309.4 +/- 17.0% of the control by 24 h (P < 0.01; n = 6). Leptin secretion was also significantly increased up to 193.3 +/- 12.1% of the control by 24 h (P < 0.01; n = 6). EPA is a ligand for peroxisome proliferator-activated receptors (PPARs) with the highest affinity to PPARalpha. We examined the effect on leptin expression of clofibrate, a ligand for PPARalpha, bezafibrate, for PPARbeta, or troglitazone, for PPARgamma, to clarify whether these ligands for PPARs could mimic EPA-induced stimulation of leptin expression. Neither clofibrate nor bezafibrate affected leptin mRNA expression, whereas troglitazone significantly suppressed leptin mRNA expression. On the other hand, inhibition by 6-diazo-5-oxo-l-norleucine of the rate-limiting enzyme in hexosamine biosynthesis blunted EPA-induced stimulation of leptin mRNA expression and its secretion. These data suggest that EPA up-regulates leptin gene expression and its secretion probably through a hexosamine biosynthetic pathway.

Uptake of 14C- and 11C-labeled glutamate, glutamine and aspartate in vitro and in vivo

To explore their potential use as in vivo tracers, the uptake of the amino acids glutamine, glutamate and aspartate, labeled with 11C or 14C, was evaluated in tumor cell aggregates, in vivo in rats and a few pilot studies with positron emission tomography (PET) in patients. The uptake in aggregates increased linearly with time, and was competitively inhibited by the same amino acids. The uptake of 14C-glutamate in carcinoid cells (BON) was inhibited by cystine but not by aspartate, contrary to the result in neuroblastoma (LAN). 6-Diazo-oxy-L-norleucine (a glutamine analogue) and Substance P had different effect on the uptake of glutamate in different cells. The metabolic fate of 14C-glutamate was evaluated with protein separation and with HPLC. The in vivo distribution in rats showed the highest uptake of 11C-glutamine and 11C-glutamate in pancreas and kidney, and of 11C-aspartate in the lung. In the human studies with PET, pancreas had the highest uptake followed by kidney with 11C-glutamate, and followed by spleen with 11C-aspartate. A primary pancreas tumour and metastases in liver were difficult to identify except in one case.

Induction of gadd153 mRNA by nutrient deprivation is overcome by glutamine

The growth arrest and DNA damage-inducible (gadd) genes are co-ordinately activated by a variety of genotoxic agents and/or growth-cessation signals. The regulation of gadd153 mRNA was investigated in renal proximal tubular epithelial cells (LLC-PK1) cultured in a nutrient- and serum-deprived medium. The addition of glutamine alone to LLC-PK1 cells cultured in Earl's balanced salt solution (EBSS) is sufficient to suppress gadd153 mRNA expression, and the removal of only glutamine from Dulbecco's modified Eagle's medium (DMEM) is also sufficient to induce gadd153 mRNA expression. Consistent with these findings, the inhibition of glutamine utilization with acivicin and 6-diazo-5-oxo-l-norleucine (DON) in cells grown in a glutamine-containing medium effectively induces gadd153 expression. Glutamine can be used as an energy source in cultured mammalian cells. However, it is unlikely that deficits in cellular energy stores (ATP) are coupled to gadd153 mRNA expression, because concentrations of ATP, UTP and GTP are all elevated in EBSS-exposed cells, and the addition of alpha-oxoglutarate to cells grown in EBSS has no effect on gadd153 mRNA expression. In contrast, concentrations of CTP decline substantially in EBSS and glutamine-deprived DMEM-cultured cells. Glutamine also serves as a precursor for the synthesis of protein and DNA. The addition of glutamine to cells grown in EBSS partly restores CTP concentrations. The addition of pyrimidine ribonucleosides (cytidine and uridine) to LLC-PK1 cells also restores CTP concentrations, in a manner commensurate with their relative abilities to overcome gadd153 expression. Finally, glutamine does not completely suppress DNA damage-induced gadd153 expression, suggesting that multiple signalling pathways lead to the expression of gadd153 mRNA under conditions of nutrient deprivation and DNA damage.

A mechanism behind the antitumour effect of 6-diazo-5-oxo-L-norleucine (DON): disruption of mitochondria

6-diazo-5-oxo-L-norleucine (DON) exerts a growth inhibitory effect selectively on the neuroendocrine tumour cell line BON and is proposed as an antitumour drug. The mechanism behind this has not yet been clarified. In the present study, transmission electron microscopy was used for the assessment of changes in cellular organelles. Furthermore, the methylthiazolyldiphenyl tetrazolium (MTT) assay for mitochondrial enzymatic activity, a fluorescent marker (rhodamine 123) for mitochondrial integrity and [2-(11)C]-acetyl-carnitine which is a substrate of the tricarboxylic acid cycle of mitochondria were employed. The studies were performed in parallel in BON and in a neuroblastoma cell line LAN, with the cells grown as monolayers or as multicellular aggregates. Severe morphological changes of intracellular organelles were observed in BON aggregates treated with low-doses of DON. Especially striking was the disruption of mitochondrial internal membrane structures. Other features included the swelling of endoplasmic reticulum, autophagocytosis of secretory granules and nuclear condensation (apoptosis). In LAN cells, no ultrastructural changes were seen after DON treatment. The MTT assay indicated inhibition of mitochondrial enzymatic activity in BON cells but not in LAN cells after 5 h treatment with DON. The mitochondrial damage was also demonstrated as a reduced metabolism of [2-(11)C]-acetyl-carnitine. The observations revealed mitochondrial damage by DON treatment and suggest that the mitochondria might be a primary target for the antitumour effect in neuroendocrine cells.

Macrophage-mediated lysis of a beta-cell line, tumour necrosis factor-alpha release from bacillus Calmette-Guérin (BCG)-activated murine macrophages and interleukin-8 release from human monocytes are dependent on extracellular glutamine concentration and glutamine metabolism

Macrophages and monocytes are cells with a large capacity for cytokine production. Cytokines produced by these cells are not preformed and released upon stimulation, but must be transcribed and translated. Although much is known concerning the regulation of the latter processes at the molecular level, the role of exogenous amino acids in the secretory process has not been actively investigated. Glutamine is utilized by macrophages at a much faster rate than any other amino acid. The role for high rates of glutamine utilization in macrophages or monocytes is not fully understood. We demonstrate here that the rates of lipopolysaccharide-stimulated tumour necrosis factor-alpha secretion from bacillus Calmette-Guérin (BCG)-activated murine peritoneal macrophages and lipopolysaccharide-stimulated interleukin-8 production from human monocytes are dependent upon extracellular glutamine concentration. We also demonstrate that potent inhibition of cytokine production can be achieved by incubating macrophages or monocytes in the presence of the glutaminase inhibitor 6-diazo-5-oxo-norleucine. On co-culture of BCG-activated macrophages and the clonal pancreatic beta-cell line BRIN-BD11, macrophage-specific beta-cell death was significantly reduced on prior exposure of macrophages to 6-diazo-5-oxo-norleucine. Thus glutamine metabolism may be essential for generation of cytotoxic products from macrophages, including tumour necrosis factor-alpha.

Importance of glutamine metabolism in murine macrophages and human monocytes to L-arginine biosynthesis and rates of nitrite or urea production

1. The intermediates of biochemical cycles are commonly utilized for biosynthetic processes; thus at least one intermediate must be replenished de novo to provide constant flux through the cycle. The utilization of L-arginine for NO synthesis in macrophages may thus reduce the concentration of intermediates of the urea cycle. It is possible that a glutamine-utilizing pathway exists in mononuclear phagocytes that may connect with the urea cycle.2. In this paper we report that mouse peritoneal resident and Bacillus Calmette-Guerin (BCG)-activated macrophages and human monocytes are capable of utilizing glutamine at high rates, contain sufficient activity of the enzymes required to convert glutamine to citrulline (and subsequently citrulline to arginine) to account for observed rates of nitrite synthesis in the absence of extracellular L-arginine, and will release nitrite when exposed to intermediates of the proposed glutamine-->arginine pathway.3. The rate of nitrite production (in the absence of extracellular arginine) was reduced by culturing macrophages or monocytes in the presence of the glutaminase inhibitor 6-diazo 5-oxo norleucine.4. The rate and extent of arginase secretion, glutamine utilization, nitrite production (basal and lipopolysaccharide-stimulated) and phosphate-dependent glutaminase activity from BCG-activated macrophages was increased compared with resident cells.5. We suggest that the elevated arginase secretion rates in activated macrophages would effectively increase the intracellular concentration of arginine available for conversion to NO via inducible nitric oxide synthase, the expression of which is known to increase on activation of macrophages or monocytes. Additionally, the rate of L-arginine biosynthesis from glutamine may be increased on immunostimulation of the macrophage.

Amino acid utilisation and deamination of glutamine and asparagine by Helicobacter pylori

Helicobacter pylori can utilise amino acids as the sole carbon energy source. The present study demonstrated that H. pylori grown in continuous culture in a defined medium containing glucose and amino acids utilised alanine, arginine, asparagine, aspartate, glutamine, glutamate, proline and serine. Specific asparaginase and glutaminase enzymes deaminated asparagine and glutamine respectively to aspartate and glutamate, with the production of ammonia. The glutaminase activity was inhibited by 6-diazo-5-oxo-L-norleucine. All the 13 strains of H. pylori tested produced both glutaminase and asparaginase activities. Glutamine is important in the health of the gastric and intestinal mucosa and is a primary energy source for lymphocytes. Depletion of glutamine at the site of H. pylori infection may be of significance in the pathogenesis of H. pylori-associated diseases such as peptic ulcer and gastric cancer.

Uridylylation of the P(II) protein in the photosynthetic bacterium Rhodospirillum rubrum

The regulatory protein P(II) has been studied in great detail in enteric bacteria; however, its function in photosynthetic bacteria has not been clearly established. As a number of these bacteria have been shown to regulate nitrogenase activity by a metabolic control system, it is of special interest to establish the role of P(II) in these diazotrophs. In this study, we show that P(II) in Rhodospirillum rubrum is modified in response to the N status in the cell and that addition of ammonium or glutamine leads to demodification. We also provide evidence that P(II) is uridylylated. In addition, we show that not only these compounds but also NAD+ promotes demodification of P(II), which is of particular interest as this pyridine nucleotide has been shown to act as a switch-off effector of nitrogenase. Demodification of P(II) by ammonium or NAD+ did not occur in cultures treated with an inhibitor of glutamine synthetase (methionine sulfoximine), whereas treatment with the glutamate synthase inhibitor 6-diazo-5-oxo-norleucine led to total demodification of P(II) without any other addition. The results indicate that P(II) probably is not directly involved in darkness switch-off of nitrogenase but that a role in ammonium switch-off cannot be excluded.

Effect of 6-diazo-5-oxo-L-norleucine (DON) on human carcinoid tumor cell aggregates

The induction of glutamine starvation has been suggested as a potential target for antitumoral treatment using inhibitors of amidotransferase, an enzyme which mediates the conversion of glutamate to glutamine. Using multicellular aggregates from tumor cell lines, the effect of treatment with a suggested glutamine antagonist, 6-diazo-5-axo-L-norleucine (DON), was investigated. As indicators of treatment response, three different parameters were measured: aggregate size, uptake of 14C-methionine and secretion of Chromogranin A. Of six cell types evaluated (carcinoid, glioma, neuroblastoma pancreas and bladder cancer), the largest inhibition of 14Cmethionine uptake, amounting to 60%, was found in the carcinoid cell line BON. In this cell line the maximum effect was reached already at 10 microM concentration. DON induced marked growth inhibition in the BON aggregates which lasted 3-4 weeks after which regrowth started. During this period the secretion of chromogranin and methionine uptake was also inhibited. These studies suggest that the neuroendocrine cell line BON is especially vulnerable to treatment by DON and show that strong inhibitory effects are found at concentrations lower than that achieved in patient blood in previous clinical trials.

gamma-Glutamyl hydrolase from human sarcoma HT-1080 cells: characterization and inhibition by glutamine antagonists

Elevated gamma-glutamyl hydrolase (GGH) activity as a contributing factor in mechanisms of acquired and intrinsic antifolate resistance has been reported for several cultured cell lines. Despite this, little is known about this enzyme, especially the human species. Using the human HT-1080 sarcoma line, we observed the secretion of GGH activity into media during culture (a phenomenon that could be markedly stimulated by exposure to NH4Cl) and an acidic pH optimum for in vitro catalytic activity of the enzyme. These properties are consistent with a lysosomal location for the enzyme. Unlike rodent GGH, preparations of HT-1080 enzyme (purified < or = 2000-fold) displayed exopeptidase activity in cleaving successive end-terminal gamma-glutamyl groups from poly-L-gamma-glutamyl derivatives of folate, methotrexate (MTX), and para-aminobenzoic acid substrates and a marked preference for long-chain polyglutamates (Km values for glu4 versus glu1 derivatives were 17- and 15-fold lower for folate and MTX versions, respectively). Using an in vitro assay screen, several glutamine antagonists [i.e., 6-diazo-5-oxo-norleucine (DON), acivicin, and azaserine] were identified as human GGH inhibitors, with DON being the most potent and displaying time-dependent inhibition. In cell culture experiments, simultaneous exposure of DON (10 microM) and [3H]MTX for 24 hr resulted in modest elevations of the long-chain gamma-glutamyl derivatives of the antifolate for HT-1080 and another human sarcoma line. These compounds may serve as useful lead compounds in the development of specific GGH inhibitors for use in examining the relationship between GGH activity and antifolate action and may potentially be used in clinical combination with antifolates that require polyglutamylation for effective cellular retention.

Glutamine protects intestinal epithelial cells: role of inducible HSP70

Glutamine (Gln) protects gut mucosa against injury and promotes mucosal healing. Because the induction of heat shock proteins (HSP) protects cells under conditions of stress, we determined whether Gln conferred protection against stress in an intestinal epithelial cell line through HSP induction. Gln added to IEC-18 cells induces an increase in HSP70, a concentration-dependent effect also seen with mRNA. Two forms of injury, lethal heat (49 degrees C) and oxidant, were used, and viability was determined by 51Cr release. Gln-treated cells were significantly more resistant to injury. Treatment with 6-diazo-5-oxo-L-norleucine (DON), a nonmetabolizable analog of Gln, induced HSP70 and protected cells from injury, but less than Gln. These findings suggest that the effects of Gln on HSP70 induction and cellular protection are mediated by metabolic and nonmetabolic mechanisms. To determine whether HSP induction was central to the action of Gln and DON, quercetin, which blocks HSP induction, was used. Quercetin blocked HSP70 induction and the protective effect of Gln and DON. We conclude that the protective effects of Gln in intestinal epithelial cells are in part mediated by HSP70 induction.

Antiviral effects of 6-diazo-5-oxo-L-norleucin on replication of herpes simplex virus type 1

An L-glutamine antagonist, 6-diazo-5-oxo-L-norleucin (L-DON), inhibits replication of vesicular stomatitis virus, poliovirus and paramyxoviruses in cultured cells. We tested the antiviral activity of L-DON against different strains of herpes simplex virus type 1 (HSV-1) in Vero cells. In the presence of a physiological plasma concentration of L-glutamine (0.5mM) L-Don inhibited 50% production of virus plaques at concentrations ranging from 7.9 to 16 microM. At concentrations of 40 microM L-Don inhibited infectious virus yield by 99%. The antiviral activity of L-DON decreased with increasing L-glutamine concentrations. A concentration of 5000 microM of L-Don had no significant effects on the viability of Vero cells. Transmission electron microscopical investigations showed that L-DON prevented mainly envelopment of viral nucleocapsids in the cytoplasm. The immunoprecipitation experiments demonstrated selective inhibition of synthesis of HSV-1 glycoproteins in L-DON treated cells. The results showed that L-DON inhibits HSV-1 replication at a late stage in the virus replication cycle, probably the cytoplasmic maturation of virions and subsequent virion egress from the cells.

Glucose metabolism to glucosamine is necessary for glucose stimulation of transforming growth factor-alpha gene transcription

Transforming growth factor-alpha (TGFalpha) gene transcription can be increased when arterial smooth muscle cells are exposed to supraphysiological concentrations of glucose, and this effect of glucose can be mimicked by glucosamine. To determine whether the metabolism of glucose to glucosamine is required for this glucose effect, the rate-limiting step in glucose metabolism to glucosamine through the enzyme glutamine:fructose-6-phosphate amidotransferase (GFAT) was blocked using pharmacological and antisense strategies. We found that blockage of GFAT activity or expression significantly blunted the glucose-induced increase of TGFalpha expression. Blockage of GFAT also resulted in a decreased RL2 signal on intracellular proteins as detected by Western blotting and indirect immunofluorescence. The RL2 monoclonal antibody recognizes an epitope on proteins that contain N-acetylglucosamine and thus is a measure of protein glycosylation. Conversely, treatment of the cells with glucose and glucosamine resulted in an increase in the RL2 epitope on intracellular proteins. These results indicate that the metabolism of glucose to glucosamine is necessary for the transcriptional stimulation of TGFalpha expression in vascular smooth muscle cells by glucose. Furthermore, the level of glycosylation of some intracellular proteins can be modulated in response to physiological changes in the extracellular glucose concentration and the net activity of GFAT.

DNA strand cleavage by tumor-inhibiting antibiotic 6-diazo-5-oxo-L-norleucine

A tumor-inhibiting antibiotic, 6-diazo-5-oxo-L-norleucine (DON), caused DNA single-strand breaks. Thus, supercoiled plasmid DNA was transformed into an open circular relaxed form DNA by incubation with DON at pH 7.4. DNA strand cleavage by DON was not inhibited by superoxide dismutase, but inhibited by catalase. The inhibition by catalase may not be due to the destruction of hydrogen peroxide, but to the masking DON by the interaction with the heme moiety of the enzyme. DNA strand cleavage by DON was inhibited by azide, mannitol, ethanol, cysteine and 2-mercaptoethanol, suggesting the involvement of radical species in the cleavage. The cleavage, however, was not suppressed by removal of dissolved oxygen from the reaction mixture, indicating that no oxygen-derived radicals participated in the cleavage. Electron spin resonance spin-trapping technique using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN) elucidated the generation of a carbon-centered radical from DON. Hence, the carbon-centered radical may participate in DNA strand cleavage by DON.

F-actin is involved in control of bovine cumulus expansion

Previously, we showed that the gonadotropin-induced expansion of bovine cumulus oophorus occurs concomitantly with the rearrangement of microfilaments (MFs) inside cumulus cell cytoplasm (Sutovský et al., 1993: Biol Reprod 49:1277-1287; Sutovský et al., 1994: Reprod Nutr Dev 34:415-425) and that cumulus expansion in cattle is accompanied by the increased expression of extracellular matrix (ECM) glycoproteins laminin and type IV collagen as well as of their actin-linked membrane receptors, integrin subunits alpha-6 and beta-1 (Sutovský and Motlík: 1994). The present study was undertaken to determine the spatial and temporal relationship between cytoskeletal rearrangement and ECM synthesis during cumulus expansion. Using electron microscopy and confocal (LSCM) and conventional fluorescence microscopy, we compared the expression of the above integrins and ECM proteins and the rearrangement of cytoskeleton in the gonadotropin-stimulated bovine oocyte cumulus complexes (OCCs) with those exposed to gonadotropin stimulation and to ECM synthesis inhibitor 6-diazo-5-oxo-L-norleucin (DON), or MF-disorganizing drug cytochalasin B (CB). In control OCCs, the 24-hr culture in the presence of follicle stimulating hormone/luteinizing hormone (FSH/LH) caused the expansion of cumuli oophori and an extensive rearrangement of MFs in the cytoplasm of cumulus cells. Concomitantly, we observed an increased deposition of laminin and type IV collagen in the intercellular spaces among cumulus cells. The redistribution of microtubules (MTs), intermediate filaments (IFs), and integrin chains alpha-6 and beta-1 also occurred at this time. The addition of 20 micrograms/ml of CB prevented cumulus expansion and accumulation of laminin and type IV collagen in the OCCs. Moreover, cytochalasin treatment blocked the redistribution of MTs and IFs, and caused the disorganization of MFs and dispersion of integrins in cumulus cells. In contrast, the distribution of integrins and cytoskeletal elements was not affected when we blocked cumulus expansion and ECM protein accumulation by DON. These data suggest that F-actin acts upstream of ECM synthesis in the cascade of events leading to the expansion of bovine cumulus ooophorus.

Determination of subunit dissociation constants in native and inactivated CTP synthetase by sedimentation equilibrium

Sedimentation equilibrium was used to correlate changes in aggregation state with active site modification of Escherichia coli CTP synthetase. The native enzyme equilibrated between monomers, dimers, and tetramers in the absence of substrates. At enzyme concentrations above 5 microM, tetramers represented 40% of the species in solution. Inactivation by 6-diazo-5-oxonorleucine (DON) or thiourea dioxide reduced the amount of tetramer to below detectable limits. However, inactivated enzyme still equilibrated between monomers and dimers. Simultaneous analysis of multispeed data at three protein concentrations yielded estimates of the dissociation constants for the monomer-dimer and dimer-tetramer equilibria. For multiple data sets of native enzyme, K1,2 was between 1 and 2 microM, and K2,4 was between 1 and 18 microM. For DON inactivated enzyme, K1,2 was 3-4 microM, and for thiourea dioxide inactivated enzyme, K1,2 was approximately 1 microM. The values for K1,2 are consistent with previously published studies by gel filtration, demonstrating that the enzyme dissociates to monomers in very dilute solution (Anderson, 1983). However, the sedimentation equilibrium experiments are the first to show that the enzyme forms tetramers in the absence of nucleotides. This result implies the presence of stable conformations in the native enzyme capable of dynamic equilibrium between monomers, dimers, and tetramers. The results presented here illustrate the sensitivity of sedimentation equilibrium for measuring the aggregation state of equilibrating enzyme species and demonstrate that active site modifications disrupt the quaternary structure of CTP synthetase.

Endogenous glutamate involvement in pulsatile secretion of gonadotropin-releasing hormone: evidence from effect of glutamine and developmental changes

The secretion of GnRH can be stimulated by glutamate (GLU) and GLU agonists, whereas GLU receptor antagonists inhibit GnRH. Using 6-diazo-5-oxo-L-norleucine (DON), an inhibitor of glutaminase, we aimed to study the involvement of endogenous GLU in GnRH secretion through the effects of impaired GLU biosynthesis from its precursor glutamine (GLN). GnRH secretion by hypothalamic explants of male rats, aged 15 and 50 days, was compared, because the frequency of spontaneous GnRH secretory pulses showed a 2-fold increase between those two ages. Using explants of 50-day-old rats, GLN elicited GnRH secretion in a similar dose-related manner as GLU. DON prevented GLN-evoked secretion of GnRH, whereas the effect of GLU was not altered. DON also markedly inhibited spontaneous pulsatile secretion of GnRH and the secretory response to veratridine, a Na+ channel opener. The inhibitory effect of DON on veratridine-evoked secretion of GnRH was directly related to the duration of exposure to DON and the frequency of GnRH secretory episodes. Using explants of 15-day-old rats, GLN could elicit GnRH release, although this response was lower than GLU-evoked secretion of GnRH. The DON concentrations required for inhibition of veratridine-evoked secretion of GnRH were lower at 15 days than at 50 days. These data indicate that 1) GLU biosynthesis from GLN is a prerequisite to the physiological mechanism of pulsatile GnRH secretion; and 2) inhibition of veratridine- or GLN-induced secretion of GnRH requires higher DON concentrations after the onset of puberty than before. This suggests that glutaminase, the enzyme controlling GLU biosynthesis from GLN, shows increased activity after the onset of puberty when the frequency of pulsatile GnRH secretion is increased as well.

Inhibition of replication of human respiratory syncytial virus by 6-diazo-5-oxo-L-norleucine

The effect of 6-diazo-5-oxo-L-norleucine (L-DON), a glutamine analog, on RSV replication was studied. At a concentration of 0.01 mM L-DON, 99% of RSV replication in treated CV-1 cells was inhibited. At this concentration of L-DON, the level of cellular protein synthesis was identical to untreated control cells. Trypan blue staining revealed that all the cells remained viable even at concentrations of L-DON as high as 10 mM. In addition, L-DON added as late as 24 h post infection can effectively suppress viral replication. Analysis of viral mRNA levels by Northern blot revealed that secondary transcription and subsequent steps in the virus life cycle were inhibited. Immunoprecipitation of viral proteins from drug treated or untreated cultures showed that synthesis of all viral proteins was drastically reduced by L-DON, with a slightly greater inhibition of viral glycoproteins. Furthermore, immunofluorescent staining showed that drug treated cells expressed both F and N proteins and that F was inserted into the membrane as the native F protein.