Oxidative stress is not required for the induction of apoptosis upon glutamine starvation of Sp2/0-Ag14 hybridoma cells

Glutamine deprivation induces metabolic adaptations associated with beta cell dysfunction and exacerbate lipotoxicity

Studies have reported that plasma glutamine is reduced in type 2 diabetes (T2D) patients. Glutamine supplementation improves glycaemic control, however the mechanisms are unclear. Here, we evaluated in vitro the pancreatic beta cell bioenergetic and insulin secretory responses to various levels of glutamine availability, or treatment in the presence of an inhibitor of intracellular glutamine metabolism. The impact of glutamine deprivation to the pathological events induced by the saturated fatty acid palmitate was also investigated. Glutamine deprivation induced a reduction in mitochondrial respiration and increase in glucose uptake and utilization. This phenotype was accompanied by impairment in beta cell function, as demonstrated by diminished insulin production and secretion, and activation of the unfolded protein response pathway. Palmitate led to insulin secretory dysfunction, loss of viability and apoptosis. Importantly, glutamine deprivation significantly exacerbated these phenotypes, suggesting that low glutamine levels could participate in the process of beta cell dysfunction in T2D.

Glutamine deprivation plus BPTES alters etoposide- and cisplatin-induced apoptosis in triple negative breast cancer cells

Glutamine provides cancer cells with the energy required to synthesize macromolecules. Methods which block glutamine metabolism in treatment of breast cancer inhibit oncogenic transformation and tumor growth. We investigated whether inhibiting glutamine metabolism produces effects that are synergistic with those produced by drugs which damage DNA in triple-negative breast cancer cells. HCC1937 and BT-549 breast cancer cells were co-treated with either cisplatin or etoposide in combination with BPTES (a specific inhibitor of glutaminase 1) or exposure to a glutamine-free medium, and the cell proliferation and cell apoptosis were measured by flow cytometry, immunoblotting studies, and CCK-8 assays. The results showed that both glutamine deprivation and BPTES pretreatments increased the toxic effects of cisplatin and etoposide on HCC1937 cells, as demonstrated by their reduced proliferation, increased expression of apoptosis-related proteins (cleaved-PARP, cleaved-caspase 9, and cleaved-caspase 3) and decreased Bcl-2/BAX ratio. However, in BT-549 cells, glutamine deprivation and BPTES treatment increased etoposide-induced apoptosis only when used with higher concentrations of etoposide, and the effect on cisplatin-induced apoptosis was minimal. These results suggest that the anti-cancer effects produced by a combined approach of inhibiting glutamine metabolism and administering common chemotherapeutic agents correlate with the tumor cell type and specific drugs being administered.

Lactate Contribution to the Tumor Microenvironment: Mechanisms, Effects on Immune Cells and Therapeutic Relevance

Malignant transformation of cells leads to enhanced glucose uptake and the conversion of a larger fraction of pyruvate into lactate, even under normoxic conditions; this phenomenon of aerobic glycolysis is largely known as the Warburg effect. This metabolic reprograming serves to generate biosynthetic precursors, thus facilitating the survival of rapidly proliferating malignant cells. Extracellular lactate directs the metabolic reprograming of tumor cells, thereby serving as an additional selective pressure. Besides tumor cells, stromal cells are another source of lactate production in the tumor microenvironment, whose role in both tumor growth and the antitumor immune response is the subject of intense research. In this review, we provide an integral perspective of the relationship between lactate and the overall tumor microenvironment, from lactate structure to metabolic pathways for its synthesis, receptors, signaling pathways, lactate-producing cells, lactate-responding cells, and how all contribute to the tumor outcome. We discuss the role of lactate as an immunosuppressor molecule that contributes to tumor evasion and we explore the possibility of targeting lactate metabolism for cancer treatment, as well as of using lactate as a prognostic biomarker.

Metabolic requirements for neutrophil extracellular traps formation

As part of the innate immune response, neutrophils are at the forefront of defence against infection, resolution of inflammation and wound healing. They are the most abundant leucocytes in the peripheral blood, have a short lifespan and an estimated turnover of 10(10) to 10(11) cells per day. Neutrophils efficiently clear microbial infections by phagocytosis and by oxygen-dependent and oxygen-independent mechanisms. In 2004, a new neutrophil anti-microbial mechanism was described, the release of neutrophil extracellular traps (NETs) composed of DNA, histones and anti-microbial peptides. Several microorganisms, bacterial products, as well as pharmacological stimuli such as PMA, were shown to induce NETs. Neutrophils contain relatively few mitochondria, and derive most of their energy from glycolysis. In this scenario we aimed to analyse some of the metabolic requirements for NET formation. Here it is shown that NETs formation is strictly dependent on glucose and to a lesser extent on glutamine, that Glut-1, glucose uptake, and glycolysis rate increase upon PMA stimulation, and that NET formation is inhibited by the glycolysis inhibitor, 2-deoxy-glucose, and to a lesser extent by the ATP synthase inhibitor oligomycin. Moreover, when neutrophils were exposed to PMA in glucose-free medium for 3 hr, they lost their characteristic polymorphic nuclei but did not release NETs. However, if glucose (but not pyruvate) was added at this time, NET release took place within minutes, suggesting that NET formation could be metabolically divided into two phases; the first, independent from exogenous glucose (chromatin decondensation) and, the second (NET release), strictly dependent on exogenous glucose and glycolysis.

Glutamine starvation enhances PCV2 replication via the phosphorylation of p38 MAPK, as promoted by reducing glutathione levels

Glutamine has a positive effect on ameliorating reproductive failure caused by porcine circovirus type 2 (PCV2). However, the mechanism by which glutamine affects PCV2 replication remains unclear. This study was conducted to investigate the effects of glutamine on PCV2 replication and its underlying mechanisms in vitro. The results show that glutamine promoted PK-15 cell viability. Surprisingly, glutamine starvation significantly increased PCV2 replication. The promotion of PCV2 replication by glutamine starvation disappeared after fresh media with 4 mM glutamine was added. Likewise, promotion of PCV2 was observed after adding buthionine sulfoximine (BSO). Glutamine starvation or BSO treatment increased the level of p38 MAPK phosphorylation and PCV2 replication in PK-15 cells. Meanwhile, p38 MAPK phosphorylation and PCV2 replication significantly decreased in p38-knockdown PK-15 cells. Promotion of PCV2 replication caused by glutamine starvation could be blocked in p38-knockdown PK-15 cells. Therefore, glutamine starvation increased PCV2 replication by promoting p38 MAPK activation, which was associated with the down regulation of intracellular glutathione levels. Our findings may contribute toward interpreting the possible pathogenic mechanism of PCV2 and provide a theoretical reference for application of glutamine in controlling porcine circovirus-associated diseases.

Dynamic process of phagocytosis and forms of macrophage cell death induced by ingestion of apoptotic neutrophils

Clearance of apoptotic neutrophils by macrophages is important for both the successful resolution of acute inflammation and homeostasis. However, the dynamic process of phagocytosis of apoptotic neutrophils by macrophages and the fate of macrophages after the ingestion of apoptotic neutrophils has not been well documented. In the present study, we staged the recognition and tethering, internalization, digestion and exocytosis steps of phagocytosis of apoptotic neutrophils. Furthermore, we found that after the ingestion of apoptotic cells, a subset of macrophages underwent cell death by autophagy, apoptosis or oncosis as revealed by transmission electron microscopy and confocal microscopy combined with specific dyes. The percentage of autophagic, apoptotic and oncotic macrophages were 8.00%±2.00%, 12.33%±2.08%, and 3.66%±1.50%, respectively. These results indicated that after ingestion of apoptotic neutrophils, a subset of macrophages undergoes autophagy and apoptosis. We propose that autophagy of macrophages after the ingestion of apoptotic cells may be a new mechanism present in the resolution of inflammation.

Glutamine deprivation induces interleukin-8 expression in ataxia telangiectasia fibroblasts

OBJECTIVE

To investigate whether glutamine deprivation induces expression of inflammatory cytokine interleukin-8 (IL-8) by determining NF-κB activity and levels of oxidative indices (ROS, reactive oxygen species; hydrogen peroxide; GSH, glutathione) in fibroblasts isolated from patients with ataxia telangiectasia (A-T).

MATERIALS

We used A-T fibroblasts stably transfected with empty vector (Mock) or with human full-length ataxia telangiectasia mutated (ATM) cDNA (YZ5) and mouse embryonic fibroblasts (MEFs) transiently transfected with ATM small interfering RNA (siRNA) or with non-specific control siRNA.

TREATMENT

The cells were cultured with or without glutamine or GSH.

METHODS

ROS levels were determined using a fluorescence reader and confocal microscopy. IL-8 or murine IL-8 homolog, keratinocyte chemoattractant (KC), and hydrogen peroxide levels in the medium were determined by enzyme-linked immunosorbent assay and colorimetric assay. GSH level was assessed by enzymatic assay, while IL-8 (KC) mRNA level was measured by reverse transcription-polymerase chain reaction (RT-PCR) and/or quantitative real-time PCR. NF-κB DNA-binding activity was determined by electrophoretic mobility shift assay. Catalase activity and ATM protein levels were determined by O2 generation and Western blotting.

RESULTS

While glutamine deprivation induced IL-8 expression and increased NF-κB DNA-binding activity in Mock cells, both processes were decreased by treatment of cells with glutamine or GSH or both glutamine and GSH. Glutamine deprivation had no effect on IL-8 expression or NF-κB DNA-binding activity in YZ5 cells. Glutamine-deprived Mock cells had higher oxidative stress indices (increases in ROS and hydrogen peroxide, reduction in GSH) than glutamine-deprived YZ5 cells. In Mock cells, glutamine deprivation-induced oxidative stress indices were suppressed by treatment with glutamine or GSH or both glutamine and GSH. GSH levels and catalase activity were lower in Mock cells than YZ5 cells. MEFs transfected with ATM siRNA and cultured without glutamine showed higher levels of ROS and IL-8 than those transfected with negative control siRNA; increased levels of ROS and IL-8 were suppressed by the treatment of glutamine.

CONCLUSION

Glutamine deprivation induces ROS production, NF-κB activation, and IL-8 expression as well as a reduction in GSH in A-T fibroblasts, all of which are attenuated by glutamine supplementation.

Protective effects of sodium selenite against aflatoxin B1-induced oxidative stress and apoptosis in broiler spleen

The aim of this study was to investigate the possible protective role of sodium selenite on aflatoxin B1-induced oxidative stress and apoptosis in spleen of broilers. Two hundred one-day-old male broilers, divided into five groups, were fed with basal diet (control group), 0.3 mg/kg AFB1 (AFB1 group), 0.3 mg/kg AFB1 + 0.2 mg/kg Se (+Se group I), 0.3 mg/kg AFB1 + 0.4 mg/kg Se (+Se group II) and 0.3 mg/kg AFB1 + 0.6 mg/kg Se (+Se group III), respectively. According to biochemical assays, AFB1 significantly decreased the activities of glutathione peroxidase, total superoxide dismutase, glutathione reductase, catalase and the level of glutathione hormone, while it increased the level of malondialdehyde. Moreover, AFB1 increased the percentage of apoptosis cells by flow cytometry and the occurrence of apoptotic cells by TUNEL assay. Simultaneous supplementation with sodium selenite restored these parameters to be close to those in control group. In conclusion, sodium selenite exhibited protective effects on AFB1-induced splenic toxicity in broilers by inhibiting oxidative stress and excessive apoptosis.

Oxidative stress parameters and anti-apoptotic response to hydroxyl radicals in fish erythrocytes: protective effects of glutamine, alanine, citrulline and proline

The present study explored the protective effects of glutamine (Gln), alanine (Ala), citrulline (Cit) and proline (Pro) on hydroxyl radical (·OH)-induced apoptosis in isolated carp erythrocytes. Hydroxyl radicals were generated by ferrous ion (Fe(2+))-mediated decomposition of hydrogen peroxide (H(2)O(2)) (Fenton reaction). In order to select an optimal ·OH concentration to induce apoptosis, cultures were treated with different concentrations of FeSO(4)/H(2)O(2) (0 μM/0 μM-50 μM/25 μM). The results showed that exposure to FeSO(4)/H(2)O(2) (0 μM/0 μM-40 μM/20 μM) increased apoptosis in a dose-dependent manner. Moreover, apoptosis was at its highest level at 40 μM FeSO(4)/20 μM H(2)O(2). We then examined the cytoprotective effects of Gln, Ala, Cit, Pro or the combination of Ala, Cit and Pro under conditions of apoptosis. Carp erythrocytes were treated with the substances listed above in the presence of 40 μM FeSO(4)/20 μM H(2)O(2) for 9 h. The controls were grown in Gln, Ala, Cit, Pro-free culture medium. The results showed that Gln, Ala, Cit, Pro and the combination of Ala, Cit and Pro effectively protected against annexin binding, decrease of forward scatter and DNA fragmentation in carp erythrocytes induced by ·OH. Furthermore, Gln, Ala, Cit, Pro and the combination of Ala, Cit and Pro effectively blocked ·OH-stimulated erythrocyte hemolysis, reduced the increase of superoxide anion and H(2)O(2) concentrations, inhibited the formation of malondialdehyde, protein carbonyls and met-hemoglobin, and prevented the decrease of superoxide dismutase, catalase and glutathione peroxidase activities and glutathione content in carp erythrocytes induced by ·OH. In addition, the results suggest that the combination of Ala, Cit and Pro produces a greater anti-apoptotic and anti-oxidative effect than their individual effects at the same concentrations. Taken together, the results showed that ·OH induces apoptosis and oxidative damage in carp erythrocytes. In addition to inhibiting apoptosis, Gln, Ala, Cit, Pro and the combination of Ala, Cit and Pro protected carp erythrocytes against oxidative damage induced by ·OH, which may be a major factor in the protection of erythrocytes from apoptosis.

Control of late apoptotic events by the p38 stress kinase in L-glutamine-deprived mouse hybridoma cells

L-Glutamine (Gln) starvation rapidly triggers apoptosis in Sp2/0-Ag14 (Sp2/0) murine hybridoma cells. Here, we report on the role played by the stress-activated kinase p38 mitogen-activated protein kinase (MAPK) in this process. p38 activation was detected 2 h after Gln withdrawal and, although treatment with the p38 inhibitor SB203580 did not prevent caspase activation in Gln-starved cells, it reduced the occurrence of both nuclear condensation/fragmentation and apoptotic body formation. Similarly, transfection of Sp2/0 cells with a dominant negative p38 MAPK reduced the incidence of nuclear pyknosis and apoptotic body formation following 2 h of Gln starvation. Gln withdrawal-induced apoptosis was blocked by the overexpression of the anti-apoptotic protein Bcl-xL or by the caspase inhibitor Z-VAD-fmk. Interestingly, Bcl-xL expression inhibited p38 activation, but Z-VAD-fmk treatment did not, indicating that activation of this MAPK occurs downstream of mitochondrial dysfunction and is independent of caspases. Moreover, the anti-oxidant N-acetyl-l-cysteine prevented p38 phosphorylation, showing that p38 activation is triggered by an oxidative stress. Altogether, our findings indicate that p38 MAPK does not contribute to the induction of apoptosis in Gln-starved Sp2/0 cells. Rather, Gln withdrawal leads to mitochondrial dysfunction, causing an oxidative stress and p38 activation, the latter contributing to the formation of late morphological features of apoptotic Sp2/0 cells.

Immunophenotyping of classic murine myeloma cell lines used for monoclonal antibody production

Murine myeloma cell lines play an important role in different areas of scientific research and are essential tools for monoclonal antibody production technology. Thus, it is important to understand the biology of these cell lines in order to provide useful information to various research fronts. The present study aims to perform detailed analyses of surface antigens expressed on three major murine myeloma cell lines extensively used for MAb production. The P3X63Ag8.653 cell line expresses molecules associated with T cell interaction (CD40(low), CD80(low)), as well as antigens related to plasma cell phenotype (CD138(high), CD184(low)). The Sp2/0-Ag14 cell line presents molecules associated with BCR activation and regulation (CD79b(low), CD22(low), CD72(med)), molecules related to T cell interaction (CD40(low), CD80(low)), and markers of plasma cell phenotype (CD138(high), CD184(low)). The NS1 cell line presents all molecules of plasma cell phenotype evaluated in this study (CD184(low), CD138(high), CD38(med)) with low expression of CD72 (CD72(low)), a molecule related to BCR activation. Molecules associated with immune response modulation such as CD23 and CD25, as well as CD117, a marker related to undifferentiated cell phenotype, were not observed in any of the three murine myeloma cell lines evaluated. These data show that in spite of their common origin and function, the immunological profiles differ between P3X63Ag8.653, Sp2/0-Ag14, and NS1 cell lines.

Exacerbated vulnerability to oxidative stress in astrocytic C6 glioma cells with stable overexpression of the glutamine transporter slc38a1

We have previously demonstrated the functional expression of glutamine (Gln) transporter (GlnT) believed to predominate in neurons for the neurotransmitter glutamate pool by rat neocortical astrocytes devoid of neuronal marker expression, with exacerbated vulnerability to oxidative stress after transient overexpression. To evaluate molecular mechanisms underlying the exacerbation, we established stable GlnT transfectants in rat astrocytic C6 glioma cells. In two different clones of stable transfectants with increased intracellular Gln levels, exposure to hydrogen peroxide (H(2)O(2)) and A23187, but not to tunicamycin or 2,4-dinitrophenol, led to significant exacerbation of the cytotoxicity compared to cells with empty vector (EV). Stable GlnT overexpression led to a significant increase in heme oxygenase-1 protein levels in a manner sensitive to H(2)O(2), whereas H(2)O(2) was significantly more effective in increasing NO(2) accumulation and reactive oxygen species (ROS) generation in stable GlnT transfectants than in EV cells. Moreover, exposure to A23187 led to a more effective increase in the generation of ROS in stable GlnT transfectants than in stable EV transfectants. These results suggest that GlnT may play a role in the mechanisms underlying the determination of cellular viability in astrocytes through modulation of intracellular ROS generation.

Q's next: the diverse functions of glutamine in metabolism, cell biology and cancer

Several decades of research have sought to characterize tumor cell metabolism in the hope that tumor-specific activities can be exploited to treat cancer. Having originated from Warburg's seminal observation of aerobic glycolysis in tumor cells, most of this attention has focused on glucose metabolism. However, since the 1950s cancer biologists have also recognized the importance of glutamine (Q) as a tumor nutrient. Glutamine contributes to essentially every core metabolic task of proliferating tumor cells: it participates in bioenergetics, supports cell defenses against oxidative stress and complements glucose metabolism in the production of macromolecules. The interest in glutamine metabolism has been heightened further by the recent findings that c-myc controls glutamine uptake and degradation, and that glutamine itself exerts influence over a number of signaling pathways that contribute to tumor growth. These observations are stimulating a renewed effort to understand the regulation of glutamine metabolism in tumors and to develop strategies to target glutamine metabolism in cancer. In this study we review the protean roles of glutamine in cancer, both in the direct support of tumor growth and in mediating some of the complex effects on whole-body metabolism that are characteristic of tumor progression.

Deficiency in glutamine but not glucose induces MYC-dependent apoptosis in human cells

The idea that conversion of glucose to ATP is an attractive target for cancer therapy has been supported in part by the observation that glucose deprivation induces apoptosis in rodent cells transduced with the proto-oncogene MYC, but not in the parental line. Here, we found that depletion of glucose killed normal human cells irrespective of induced MYC activity and by a mechanism different from apoptosis. However, depletion of glutamine, another major nutrient consumed by cancer cells, induced apoptosis depending on MYC activity. This apoptosis was preceded by depletion of the Krebs cycle intermediates, was prevented by two Krebs cycle substrates, but was unrelated to ATP synthesis or several other reported consequences of glutamine starvation. Our results suggest that the fate of normal human cells should be considered in evaluating nutrient deprivation as a strategy for cancer therapy, and that understanding how glutamine metabolism is linked to cell viability might provide new approaches for treatment of cancer.

Upregulation of the glutamine transporter through transactivation mediated by cAMP/protein kinase A signals toward exacerbation of vulnerability to oxidative stress in rat neocortical astrocytes

In the present study, we have evaluated the possible functionality in astrocytes of the glutamine (Gln) transporter (GlnT) known to predominate in neurons for the neurotransmitter pool of glutamate. Sustained exposure to the adenylyl cyclase activator forskolin for 24 h led to a significant increase in mRNA expression of GlnT among different membrane transporters capable of transporting Gln, with an increase in [(3)H]Gln accumulation sensitive to a system A transporter inhibitor, in cultured rat neocortical astrocytes, but not neurons. Forskolin drastically stimulated GlnT promoter activity in a manner sensitive to a protein kinase A (PKA) inhibitor in rat astrocytic C6 glioma cells, while deletion mutation analysis revealed that the stimulation was mediated by a cAMP responsive element (CRE)/activator protein-1 (AP-1) like site located on GlnT gene promoter. Forskolin drastically stimulated the promoter activity in a fashion sensitive to a PKA inhibitor in C6 glioma cells transfected with a CRE or AP-1 reporter plasmid, in association with the phosphorylation of CRE binding protein on serine133. Transient overexpression of GlnT significantly exacerbated the cytotoxicity of hydrogen peroxide in cultured astrocytes. These results suggest that GlnT expression is upregulated by cAMP/PKA signals for subsequent exacerbation of the vulnerability to oxidative stress in astrocytes.