The neurotransmitter glutamate is neurotoxic when it is accumulated in a massive amount in the extracellular f luid. Excessive release of glutamate has been shown to be a major cause of neuronal degeneration after central nervous system injury. Under normal conditions, accumulation of synaptically released glutamate is prevented, at least in part, by a glial uptake system in which the glia-specific enzyme glutamine synthetase (GS) plays a key role. We postulated that glial cells cannot cope with glutamate neurotoxicity because the level of GS is not high enough to catalyze the excessive amounts of glutamate released by damaged neurons. We examined whether elevation of GS expression in glial cells protects against neuronal degeneration in injured retinal tissue. Analysis of lactate dehydrogenase eff lux, DNA fragmentation, and histological sections revealed that hormonal induction of the endogenous GS gene in retinal glial cells correlates with a decline in neuronal degeneration, whereas inhibition of GS activity by methionine sulfoximine leads to increased cell death. A supply of purified GS enzyme to the culture medium of retinal explants or directly to the embryo in ovo causes a dose-dependent decline in the extent of cell death. These results show that GS is a potent neuroprotectant and that elevation of GS expression in glial cells activates an endogenous mechanism whereby neurons are protected from the deleterious effects of excess glutamate in extracellular f luid after trauma or ischemia. Our results suggest new approaches to the clinical handling of neuronal degeneration.Glutamate neurotoxicity plays an important role in the process of neuronal degeneration after trauma or focal ischemia (for reviews, see refs. 1 and 2). Glutamate, a neurotransmitter that mediates normal excitatory synaptic transmission by interaction with postsynaptic receptors, is neurotoxic when present in excessive amounts. Injured neurons release massive amounts of glutamate, which induce neuronal cell death by continuous overexcitation of postsynaptic receptors. In this way, the initial trauma is amplified and causes the damage to spread to neighboring cells. Under normal conditions, the synaptically released glutamate is taken up into glial cells, where it is converted into glutamine by the glia-specific enzyme glutamine synthetase [GS; L-glutamate:ammonia ligase (ADPforming); EC 6.3.1.2]; glutamine reenters the neurons and is hydrolyzed by glutaminase to form glutamate, thus replenishing the neurotransmitter pool (3, 4). This biochemical pathway fails, however, to prevent glutamate neurotoxicity after insult. We hypothesized that GS is a limiting factor in this process and that its level in glial cells is not high enough to catalyze the excessive amounts of glutamate released by damaged cells. If this is the case, an increase in GS expression should have neuroprotective benefits.To examine the neuroprotective potential of GS, it is necessary to employ an experimental system in which expression of GS can be modulated. The ...

The glucocorticoid signaling pathway is responsive to a considerable number of internal and external signals and can therefore establish diverse patterns of gene expression. A glial‐specific pattern, for example, is shown by the glucocorticoid‐inducible gene glutamine synthetase. The enzyme is expressed at a particularly high level in glial cells, where it catalyzes the recycling of the neurotransmitter glutamate, and at a low level in most other cells, for housekeeping duties. Glial specificity of glutamine synthetase induction is achieved by the use of positive and negative regulatory elements, a glucocorticoid response element and a neural restrictive silencer element. Though not glial specific by themselves, these elements may establish a glial‐specific pattern of expression through their mutual activity and their combined effect. The inductive activity of glucocorticoids is markedly repressed by the c‐Jun protein, which is expressed at relatively high levels in proliferating glial cells. The signaling pathway of c‐Jun is activated by the disruption of glia–neuron cell contacts, by transformation with v‐src, and in proliferating retinal cells of early embryonic ages. The c‐Jun protein inhibits the transcriptional activity of the glucocorticoid receptor and thus represses glutamine synthetase expression. This repressive mechanism might also affect the ability of glial cells to cope with glutamate neurotoxicity in injured tissues. © 1999 John Wiley & Sons, Inc. J Neurobiol 40: 513–527, 1999

Objectives. This study aimed to evaluate the efficacy and safety of once-per-cycle balugrastim versus pegfilgrastim for neutrophil support in breast cancer patients receiving myelosuppressive chemotherapy. Methods. Breast cancer patients (n 5 256) were randomized to 40 or 50 mg of subcutaneous balugrastim or 6 mg of pegfilgrastim 24 hours after chemotherapy (60 mg/m 2 doxorubicin and 75 mg/m 2 docetaxel, every 21 days for up to 4 cycles). The primary efficacy parameter was the duration of severe neutropenia (DSN) in cycle 1. Secondary parameters included DSN (cycles 2-4), absolute neutrophil count (ANC) nadir, febrile neutropenia rates, and time to ANC recovery (cycles 1-4). Safety, pharmacokinetics, and immunogenicity were assessed.Results. Mean cycle 1 DSN was 1.0 day with 40 mg of balugrastim, 1.3with50mgofbalugrastim,and1.2withpegfilgrastim(upperlimit of 95% confidence intervals for between-group DSN differences was ,1.0 day for both balugrastim doses versus pegfilgrastim). Between-group efficacy parameters were comparable except for time to ANC recovery in cycle 1 (40 mg of balugrastim, 2.0 days; 50 mg of balugrastim, 2.1; pegfilgrastim, 2.6). Median terminal elimination half-life was 37 hours for 40 mg of balugrastim, 36 for 50 mg of balugrastim, and 45 for pegfilgrastim. Antibody response to balugrastim was low and transient, with no neutralizing effect. Conclusion. Once-per-cycle balugrastim is not inferior to pegfilgrastim in reducing cycle 1 DSN in breast cancer patients receiving chemotherapy; both drugs have comparable safety profiles. The Oncologist 2016;21:7-15 Implications for Practice: This paper provides efficacy and safety data for a new, once-per-cycle granulocyte colony-stimulating factor, balugrastim, for the prevention of chemotherapy-induced neutropenia in patients with breast cancer receiving myelosuppressive chemotherapy. In this phase III trial, balugrastim was shown to be not inferior to pegfilgrastim in the duration of severe neutropenia in cycle 1 of doxorubicin/docetaxel chemotherapy, and the safety profiles of the two agents were similar. Once-per-cycle balugrastim is a safe and effective alternative to pegfilgrastim for hematopoietic support in patients with breast cancer receiving myelosuppressive chemotherapy associated with a greater than 20% risk of developing febrile neutropenia.

No abstract

Balugrastim is a once-per-cycle, fixed-dose recombinant protein comprising human serum albumin and granulocyte colony-stimulating factor under development for prevention of severe neutropenia in cancer patients receiving myelosuppressive chemotherapy. This phase II, multicenter, active-controlled, dose-finding pilot study evaluated balugrastim safety and efficacy versus pegfilgrastim in breast cancer patients scheduled to receive myelosuppressive chemotherapy and investigated two doses with similar efficacy to pegfilgrastim for a subsequent phase III study. Patients received four cycles of doxorubicin/docetaxel chemotherapy and with each successive cycle were randomized sequentially to escalating doses of balugrastim [30 (n = 11), 40 (n = 21), or 50 mg (n = 20)] or a fixed dose of pegfilgrastim [6 mg (n = 26)] post-chemotherapy. Balugrastim doses were escalated as planned. The incidence of adverse events was similar among the balugrastim groups and between all balugrastim doses and pegfilgrastim. The most frequently reported adverse events were neutropenia, alopecia, and nausea. During cycle 1, severe neutropenia (absolute neutrophil count of <0.5 × 10(9)/L) occurred in 40, 67, and 50 % and febrile neutropenia occurred in 20.0, 9.5, and 10.0 % of patients receiving balugrastim 30, 40, and 50 mg, respectively; in patients receiving pegfilgrastim, 48 % experienced severe neutropenia and 8 % experienced febrile neutropenia. Duration of severe neutropenia (DSN) for each treatment group was 0.9, 1.6, 1.1, and 0.9 days, respectively. In the remaining three chemotherapy cycles, DSN was ≤1 day across all treatment groups. Balugrastim 50 mg was comparable to pegfilgrastim in terms of safety and overall efficacy in breast cancer patients receiving myelosuppressive chemotherapy.

Glutamine synthetase is a key enzyme in the recycling of the neurotransmitter glutamate. Expression of this enzyme is regulated by glucocorticoids, which induce a high level of glutamine synthetase in neural but not in various non-neural tissues. This is despite the fact that non-neural cells express functional glucocorticoid receptor molecules capable of inducing other target genes. Sequencing and functional analysis of the upstream region of the glutamine synthetase gene identified, 5 to the glucocorticoid response element (GRE), a 21-base pair glutamine synthetase silencer element (GSSE), which showed considerable homology with the neural restrictive silencer element NRSE. The GSSE was able to markedly repress the induction of gene transcription by glucocorticoids in non-neural cells and in embryonic neural retina. The repressive activity of the GSSE could be conferred on a heterologous GRE promoter and was orientation-and position-independent with respect to the transcriptional start site, but appeared to depend on a location proximal to the GRE. Gel-shift assays revealed that non-neural cells and cells of early embryonic retina contain a high level of GSSE binding activity and that this level declines progressively with age. Our results suggest that the GSSE might be involved in the restriction of glutamine synthetase induction by glucocorticoids to differentiated neural tissues.Glutamine synthetase (GS 1 ; L-glutamate:ammonia ligase (ADP-forming); EC 6.3.1.2) is a "housekeeping" enzyme that is expressed at a particularly high level in neural tissues (1, 2). High levels of GS expression are restricted to glial cells (1,(3)(4)(5) and are essential for the recycling of the neurotransmitter glutamate. Synaptically released glutamate is taken up into glial cells, where it is converted by GS into glutamine, which re-enters the neurons and is hydrolyzed by glutaminase to form glutamate again (6, 7). In this way, the neurotransmitter pool is replenished and glutamate neurotoxicity is prevented.Studies in the chicken neural retina showed that GS expression is regulated by systemic glucocorticoids, which induce in this tissue a very high level of GS by directly stimulating the transcription of the gene (8 -10). The ability of glucocorticoids to induce GS expression is developmentally controlled. Glucocorticoids can induce a high level of GS expression in neural retina at late embryonic ages, but not in early embryonic retina (2, 11-13). The direct involvement of glucocorticoids in the control of GS gene transcription is evidenced by the nuclear run-on transcription assay, as well as by the finding that the upstream region of the GS gene contains a glucocorticoid response element (GRE) that can bind the glucocorticoid receptor protein and confer responsiveness to glucocorticoids on an attached reporter gene (8 -10, 14, 15). This mode of regulation, which is dependent on the presence of active glucocorticoid receptor molecules, explains the cell type specificity of GS expression in the neural retina; GS expression is ...

Balugrastim was well tolerated in this small population of breast cancer patients.

Although Barrett's esophagus has been recognized for over 50 years, the cellular and molecular mechanisms leading to the replacement of squamous esophageal epithelium with a columnar type are largely unknown. Barrett's is known to be an acquired process secondary to chronic gastroesophageal reflux disease and occurs in the presence of severe disruption of the gastroesophageal barrier and reflux of a mixture of gastric and duodenal content. Current hypothesis suggest that epithelial change occurs due to stimulation of esophageal stem cells present in the basal layers of the epithelium or submucosal glands, toward a columnar epithelial differentiation pathway. The transcription factor CDX2 seems to play a key role in promoting the cellular biology necessary for columnar differentiation, and can be induced by bile salt and acid stimulation. Several cellular signaling pathways responsible for modulation of intestinal differentiation have also been identified and include WNT, Notch, BMP, Sonic HH and TGFB. These also have been shown to respond to stimulation by bile acids, acid or both and may influence CDX2 expression. Their relative activity within the stem cell population is almost certainly responsible for the development of the esophageal columnar epithelial phenotype we know as Barrett's esophagus.